QString 类提供 Unicode 字符串。 更多...
头: | #include <QString> |
CMake: |
find_package(Qt6 REQUIRED COMPONENTS Core)
target_link_libraries(mytarget PRIVATE Qt6::Core) |
qmake: | QT += core |
注意: 此类的所有函数 可重入 .
ConstIterator | |
Iterator | |
enum | NormalizationForm { NormalizationForm_D, NormalizationForm_C, NormalizationForm_KD, NormalizationForm_KC } |
enum | SectionFlag { SectionDefault, SectionSkipEmpty, SectionIncludeLeadingSep, SectionIncludeTrailingSep, SectionCaseInsensitiveSeps } |
flags | SectionFlags |
const_iterator | |
const_pointer | |
const_reference | |
const_reverse_iterator | |
difference_type | |
iterator | |
pointer | |
reference | |
reverse_iterator | |
size_type | |
value_type |
QString () | |
QString (const QChar * unicode , qsizetype size = -1) | |
QString (QChar ch ) | |
QString (qsizetype size , QChar ch ) | |
QString (QLatin1StringView str ) | |
QString (const char8_t * str ) | |
QString (const char * str ) | |
QString (const QByteArray & ba ) | |
QString (const QString & other ) | |
QString (QString && other ) | |
~QString () | |
QString & | append (const QString & str ) |
QString & | append (QChar ch ) |
QString & | append (const QChar * str , qsizetype len ) |
QString & | append (QStringView v ) |
QString & | append (QLatin1StringView str ) |
QString & | append (QUtf8StringView str ) |
QString & | append (const char * str ) |
QString & | append (const QByteArray & ba ) |
QString | arg (const QString & a , int fieldWidth = 0, QChar fillChar = u' ') const |
QString | arg (qlonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const |
QString | arg (qulonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const |
QString | arg (long a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const |
QString | arg (ulong a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const |
QString | arg (int a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const |
QString | arg (uint a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const |
QString | arg (short a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const |
QString | arg (ushort a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const |
QString | arg (double a , int fieldWidth = 0, char format = 'g', int precision = -1, QChar fillChar = u' ') const |
QString | arg (char a , int fieldWidth = 0, QChar fillChar = u' ') const |
QString | arg (QChar a , int fieldWidth = 0, QChar fillChar = u' ') const |
QString | arg (QStringView a , int fieldWidth = 0, QChar fillChar = u' ') const |
QString | arg (QLatin1StringView a , int fieldWidth = 0, QChar fillChar = u' ') const |
QString | arg (Args &&... args ) const |
const QChar | at (qsizetype position ) const |
QChar | back () const |
QChar & | back () |
QString::iterator | begin () |
QString::const_iterator | begin () const |
qsizetype | capacity () const |
QString::const_iterator | cbegin () const |
QString::const_iterator | cend () const |
void | chop (qsizetype n ) |
QString | chopped (qsizetype len ) const |
void | clear () |
int | compare (const QString & other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
int | compare (QLatin1StringView other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
int | compare (QStringView s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
int | compare (QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
QString::const_iterator | constBegin () const |
const QChar * | constData () const |
QString::const_iterator | constEnd () const |
bool | contains (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | contains (QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | contains (QLatin1StringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | contains (QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | contains (const QRegularExpression & re , QRegularExpressionMatch * rmatch = nullptr) const |
qsizetype | count (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | count (QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | count (QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | count (const QRegularExpression & re ) const |
QString::const_reverse_iterator | crbegin () const |
QString::const_reverse_iterator | crend () const |
QChar * | data () |
const QChar * | data () const |
QString::iterator | end () |
QString::const_iterator | end () const |
bool | endsWith (const QString & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | endsWith (QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | endsWith (QLatin1StringView s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | endsWith (QChar c , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
QString::iterator | erase (QString::const_iterator first , QString::const_iterator last ) |
QString::iterator | erase (QString::const_iterator it ) |
QString & | fill (QChar ch , qsizetype size = -1) |
QString | first (qsizetype n ) const |
QChar | front () const |
QChar & | front () |
qsizetype | indexOf (QLatin1StringView str , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | indexOf (QChar ch , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | indexOf (const QString & str , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | indexOf (QStringView str , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | indexOf (const QRegularExpression & re , qsizetype from = 0, QRegularExpressionMatch * rmatch = nullptr) const |
QString & | insert (qsizetype position , const QString & str ) |
QString & | insert (qsizetype position , QChar ch ) |
QString & | insert (qsizetype position , const QChar * unicode , qsizetype size ) |
QString & | insert (qsizetype position , QStringView str ) |
QString & | insert (qsizetype position , QLatin1StringView str ) |
QString & | insert (qsizetype position , QUtf8StringView str ) |
QString & | insert (qsizetype position , const char * str ) |
QString & | insert (qsizetype position , const QByteArray & str ) |
bool | isEmpty () const |
bool | isLower () const |
bool | isNull () const |
bool | isRightToLeft () const |
bool | isUpper () const |
bool | isValidUtf16 () const |
QString | last (qsizetype n ) const |
qsizetype | lastIndexOf (const QString & str , qsizetype from , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | lastIndexOf (QChar c , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | lastIndexOf (QChar ch , qsizetype from , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | lastIndexOf (QLatin1StringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | lastIndexOf (QLatin1StringView str , qsizetype from , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | lastIndexOf (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | lastIndexOf (QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | lastIndexOf (QStringView str , qsizetype from , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
qsizetype | lastIndexOf (const QRegularExpression & re , QRegularExpressionMatch * rmatch = nullptr) const |
qsizetype | lastIndexOf (const QRegularExpression & re , qsizetype from , QRegularExpressionMatch * rmatch = nullptr) const |
QString | left (qsizetype n ) const |
QString | leftJustified (qsizetype width , QChar fill = u' ', bool truncate = false) const |
qsizetype | length () const |
int | localeAwareCompare (const QString & other ) const |
int | localeAwareCompare (QStringView other ) const |
QString | mid (qsizetype position , qsizetype n = -1) const |
QString | normalized (QString::NormalizationForm mode , QChar::UnicodeVersion version = QChar::Unicode_Unassigned) const |
QString & | prepend (const QString & str ) |
QString & | prepend (QChar ch ) |
QString & | prepend (const QChar * str , qsizetype len ) |
QString & | prepend (QStringView str ) |
QString & | prepend (QLatin1StringView str ) |
QString & | prepend (QUtf8StringView str ) |
QString & | prepend (const char * str ) |
QString & | prepend (const QByteArray & ba ) |
void | push_back (const QString & other ) |
void | push_back (QChar ch ) |
void | push_front (const QString & other ) |
void | push_front (QChar ch ) |
QString::reverse_iterator | rbegin () |
QString::const_reverse_iterator | rbegin () const |
QString & | remove (qsizetype position , qsizetype n ) |
QString & | remove (QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | remove (QLatin1StringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | remove (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | remove (const QRegularExpression & re ) |
QString & | removeAt (qsizetype pos ) |
QString & | removeFirst () |
QString & | removeIf (Predicate pred ) |
QString & | removeLast () |
QString::reverse_iterator | rend () |
QString::const_reverse_iterator | rend () const |
QString | repeated (qsizetype times ) const |
QString & | replace (qsizetype position , qsizetype n , const QString & after ) |
QString & | replace (qsizetype position , qsizetype n , QChar after ) |
QString & | replace (qsizetype position , qsizetype n , const QChar * unicode , qsizetype size ) |
QString & | replace (QChar before , QChar after , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | replace (const QChar * before , qsizetype blen , const QChar * after , qsizetype alen , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | replace (QLatin1StringView before , QLatin1StringView after , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | replace (QLatin1StringView before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | replace (const QString & before , QLatin1StringView after , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | replace (const QString & before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | replace (QChar ch , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | replace (QChar c , QLatin1StringView after , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString & | replace (const QRegularExpression & re , const QString & after ) |
void | reserve (qsizetype size ) |
void | resize (qsizetype size ) |
void | resize (qsizetype newSize , QChar fillChar ) |
QString | right (qsizetype n ) const |
QString | rightJustified (qsizetype width , QChar fill = u' ', bool truncate = false) const |
QString | section (QChar sep , qsizetype start , qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const |
QString | section (const QString & sep , qsizetype start , qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const |
QString | section (const QRegularExpression & re , qsizetype start , qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const |
QString & | setNum (int n , int base = 10) |
QString & | setNum (short n , int base = 10) |
QString & | setNum (ushort n , int base = 10) |
QString & | setNum (uint n , int base = 10) |
QString & | setNum (long n , int base = 10) |
QString & | setNum (ulong n , int base = 10) |
QString & | setNum (qlonglong n , int base = 10) |
QString & | setNum (qulonglong n , int base = 10) |
QString & | setNum (float n , char format = 'g', int precision = 6) |
QString & | setNum (double n , char format = 'g', int precision = 6) |
QString & | setRawData (const QChar * unicode , qsizetype size ) |
QString & | setUnicode (const QChar * unicode , qsizetype size ) |
QString & | setUtf16 (const ushort * unicode , qsizetype size ) |
void | shrink_to_fit () |
QString | simplified () const |
qsizetype | size () const |
QString | sliced (qsizetype pos , qsizetype n ) const |
QString | sliced (qsizetype pos ) const |
QStringList | split (const QString & sep , Qt::SplitBehavior behavior = Qt::KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
QStringList | split (QChar sep , Qt::SplitBehavior behavior = Qt::KeepEmptyParts, Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
QStringList | split (const QRegularExpression & re , Qt::SplitBehavior behavior = Qt::KeepEmptyParts) const |
void | squeeze () |
bool | startsWith (const QString & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | startsWith (QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | startsWith (QLatin1StringView s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
bool | startsWith (QChar c , Qt::CaseSensitivity cs = Qt::CaseSensitive) const |
void | swap (QString & other ) |
CFStringRef | toCFString () const |
QString | toCaseFolded () const |
double | toDouble (bool * ok = nullptr) const |
float | toFloat (bool * ok = nullptr) const |
QString | toHtmlEscaped () const |
int | toInt (bool * ok = nullptr, int base = 10) const |
QByteArray | toLatin1 () const |
QByteArray | toLocal8Bit () const |
long | toLong (bool * ok = nullptr, int base = 10) const |
qlonglong | toLongLong (bool * ok = nullptr, int base = 10) const |
QString | toLower () const |
NSString * | toNSString () const |
short | toShort (bool * ok = nullptr, int base = 10) const |
std::string | toStdString () const |
std::u16string | toStdU16String () const |
std::u32string | toStdU32String () const |
std::wstring | toStdWString () const |
uint | toUInt (bool * ok = nullptr, int base = 10) const |
ulong | toULong (bool * ok = nullptr, int base = 10) const |
qulonglong | toULongLong (bool * ok = nullptr, int base = 10) const |
ushort | toUShort (bool * ok = nullptr, int base = 10) const |
QList<uint> | toUcs4 () const |
QString | toUpper () const |
QByteArray | toUtf8 () const |
qsizetype | toWCharArray (wchar_t * array ) const |
decltype(qTokenize(*this, std::forward<Needle>(needle), flags...)) | tokenize (Needle && sep , Flags... flags ) const & |
decltype(qTokenize(std::move(*this), std::forward<Needle>(needle), flags...)) | tokenize (Needle && sep , Flags... flags ) const && |
decltype(qTokenize(std::move(*this), std::forward<Needle>(needle), flags...)) | tokenize (Needle && sep , Flags... flags ) && |
QString | trimmed () const |
void | truncate (qsizetype position ) |
const QChar * | unicode () const |
const ushort * | utf16 () const |
bool | operator!= (const char * other ) const |
bool | operator!= (const QByteArray & other ) const |
QString & | operator+= (const QString & other ) |
QString & | operator+= (QChar ch ) |
QString & | operator+= (QStringView str ) |
QString & | operator+= (QLatin1StringView str ) |
QString & | operator+= (QUtf8StringView str ) |
QString & | operator+= (const char * str ) |
QString & | operator+= (const QByteArray & ba ) |
bool | operator< (const char * other ) const |
bool | operator< (const QByteArray & other ) const |
bool | operator<= (const char * other ) const |
bool | operator<= (const QByteArray & other ) const |
QString & | operator= (const QString & other ) |
QString & | operator= (QChar ch ) |
QString & | operator= (QLatin1StringView str ) |
QString & | operator= (QString && other ) |
QString & | operator= (const char * str ) |
QString & | operator= (const QByteArray & ba ) |
bool | operator== (const char * other ) const |
bool | operator== (const QByteArray & other ) const |
bool | operator> (const char * other ) const |
bool | operator> (const QByteArray & other ) const |
bool | operator>= (const char * other ) const |
bool | operator>= (const QByteArray & other ) const |
QChar & | operator[] (qsizetype position ) |
const QChar | operator[] (qsizetype position ) const |
QString | asprintf (const char * cformat , ...) |
int | compare (const QString & s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
int | compare (const QString & s1 , QLatin1StringView s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
int | compare (QLatin1StringView s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
int | compare (const QString & s1 , QStringView s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
int | compare (QStringView s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive) |
QString | fromCFString (CFStringRef string ) |
QString | fromLatin1 (const char * str , qsizetype size ) |
QString | fromLatin1 (QByteArrayView str ) |
QString | fromLatin1 (const QByteArray & str ) |
QString | fromLocal8Bit (const char * str , qsizetype size ) |
QString | fromLocal8Bit (QByteArrayView str ) |
QString | fromLocal8Bit (const QByteArray & str ) |
QString | fromNSString (const NSString * string ) |
QString | fromRawData (const QChar * unicode , qsizetype size ) |
QString | fromStdString (const std::string & str ) |
QString | fromStdU16String (const std::u16string & str ) |
QString | fromStdU32String (const std::u32string & str ) |
QString | fromStdWString (const std::wstring & str ) |
QString | fromUcs4 (const char32_t * unicode , qsizetype size = -1) |
QString | fromUtf8 (const char * str , qsizetype size ) |
QString | fromUtf8 (QByteArrayView str ) |
QString | fromUtf8 (const QByteArray & str ) |
QString | fromUtf8 (const char8_t * str ) |
QString | fromUtf8 (const char8_t * str , qsizetype size ) |
QString | fromUtf16 (const char16_t * unicode , qsizetype size = -1) |
QString | fromWCharArray (const wchar_t * string , qsizetype size = -1) |
int | localeAwareCompare (const QString & s1 , const QString & s2 ) |
int | localeAwareCompare (QStringView s1 , QStringView s2 ) |
QString | number (long n , int base = 10) |
QString | number (int n , int base = 10) |
QString | number (uint n , int base = 10) |
QString | number (ulong n , int base = 10) |
QString | number (qlonglong n , int base = 10) |
QString | number (qulonglong n , int base = 10) |
QString | number (double n , char format = 'g', int precision = 6) |
QString | vasprintf (const char * cformat , va_list ap ) |
qsizetype | erase (QString & s , const T & t ) |
qsizetype | erase_if (QString & s , Predicate pred ) |
bool | operator!= (const QString & s1 , const QString & s2 ) |
bool | operator!= (const QString & s1 , QLatin1StringView s2 ) |
bool | operator!= (const char * s1 , const QString & s2 ) |
QString | operator""_s (const char16_t * str , size_t size ) |
QString | operator+ (const QString & s1 , const QString & s2 ) |
QString | operator+ (QString && s1 , const QString & s2 ) |
QString | operator+ (const QString & s1 , const char * s2 ) |
QString | operator+ (const char * s1 , const QString & s2 ) |
bool | operator< (const QString & s1 , const QString & s2 ) |
bool | operator< (const QString & s1 , QLatin1StringView s2 ) |
bool | operator< (QLatin1StringView s1 , const QString & s2 ) |
bool | operator< (const char * s1 , const QString & s2 ) |
QDataStream & | operator<< (QDataStream & stream , const QString & string ) |
bool | operator<= (const QString & s1 , const QString & s2 ) |
bool | operator<= (const QString & s1 , QLatin1StringView s2 ) |
bool | operator<= (QLatin1StringView s1 , const QString & s2 ) |
bool | operator<= (const char * s1 , const QString & s2 ) |
bool | operator== (const QString & s1 , const QString & s2 ) |
bool | operator== (const QString & s1 , QLatin1StringView s2 ) |
bool | operator== (QLatin1StringView s1 , const QString & s2 ) |
bool | operator== (const char * s1 , const QString & s2 ) |
bool | operator> (const QString & s1 , const QString & s2 ) |
bool | operator> (const QString & s1 , QLatin1StringView s2 ) |
bool | operator> (QLatin1StringView s1 , const QString & s2 ) |
bool | operator> (const char * s1 , const QString & s2 ) |
bool | operator>= (const QString & s1 , const QString & s2 ) |
bool | operator>= (const QString & s1 , QLatin1StringView s2 ) |
bool | operator>= (QLatin1StringView s1 , const QString & s2 ) |
bool | operator>= (const char * s1 , const QString & s2 ) |
QDataStream & | operator>> (QDataStream & stream , QString & string ) |
QStringLiteral ( str ) | |
QT_NO_CAST_FROM_ASCII | |
QT_NO_CAST_TO_ASCII | |
QT_RESTRICTED_CAST_FROM_ASCII | |
const char * | qPrintable (const QString & str ) |
const wchar_t * | qUtf16Printable (const QString & str ) |
const char * | qUtf8Printable (const QString & str ) |
QString 存储字符串的 16 位 QChar ,其中各 QChar corresponds to one UTF-16 code unit. (Unicode characters with code values above 65535 are stored using surrogate pairs, i.e., two consecutive QChar s.)
Unicode is an international standard that supports most of the writing systems in use today. It is a superset of US-ASCII (ANSI X3.4-1986) and Latin-1 (ISO 8859-1), and all the US-ASCII/Latin-1 characters are available at the same code positions.
Behind the scenes, QString uses 隐式共享 (copy-on-write) to reduce memory usage and to avoid the needless copying of data. This also helps reduce the inherent overhead of storing 16-bit characters instead of 8-bit characters.
In addition to QString, Qt also provides the QByteArray class to store raw bytes and traditional 8-bit '\0'-terminated strings. For most purposes, QString is the class you want to use. It is used throughout the Qt API, and the Unicode support ensures that your applications will be easy to translate if you want to expand your application's market at some point. The two main cases where QByteArray is appropriate are when you need to store raw binary data, and when memory conservation is critical (like in embedded systems).
One way to initialize a QString is simply to pass a
const char *
to its constructor. For example, the following code creates a QString of size 5 containing the data "Hello":
QString str = "Hello";
QString 转换
const char *
数据成 Unicode 使用
fromUtf8
() 函数。
In all of the QString functions that take
const char *
parameters, the
const char *
is interpreted as a classic C-style '\0'-terminated string encoded in UTF-8. It is legal for the
const char *
parameter to be
nullptr
.
You can also provide string data as an array of QChar s:
static const QChar data[4] = { 0x0055, 0x006e, 0x10e3, 0x03a3 }; QString str(data, 4);
QString makes a deep copy of the QChar data, so you can modify it later without experiencing side effects. (If for performance reasons you don't want to take a deep copy of the character data, use QString::fromRawData () instead.)
Another approach is to set the size of the string using
resize
() and to initialize the data character per character. QString uses 0-based indexes, just like C++ arrays. To access the character at a particular index position, you can use
operator[]
(). On non-
const
strings,
operator[]
() returns a reference to a character that can be used on the left side of an assignment. For example:
QString str; str.resize(4); str[0] = QChar('U'); str[1] = QChar('n'); str[2] = QChar(0x10e3); str[3] = QChar(0x03a3);
For read-only access, an alternative syntax is to use the at () 函数:
QString str; for (qsizetype i = 0; i < str.size(); ++i) { if (str.at(i) >= QChar('a') && str.at(i) <= QChar('f')) qDebug() << "Found character in range [a-f]"; }
The at () function can be faster than operator[] (), because it never causes a 深拷贝 to occur. Alternatively, use the first (), last (),或 sliced () functions to extract several characters at a time.
A QString can embed '\0' characters ( QChar::Null ). The size () function always returns the size of the whole string, including embedded '\0' characters.
After a call to the resize () function, newly allocated characters have undefined values. To set all the characters in the string to a particular value, use the fill () 函数。
QString provides dozens of overloads designed to simplify string usage. For example, if you want to compare a QString with a string literal, you can write code like this and it will work as expected:
QString str; if (str == "auto" || str == "extern" || str == "static" || str == "register") { // ... }
You can also pass string literals to functions that take QStrings as arguments, invoking the QString(const char *) constructor. Similarly, you can pass a QString to a function that takes a
const char *
argument using the
qPrintable
() macro which returns the given QString as a
const char *
. This is equivalent to calling <QString>.
toLocal8Bit
().
constData
().
QString provides the following basic functions for modifying the character data: append (), prepend (), insert (), replace (),和 remove ()。例如:
QString str = "and"; str.prepend("rock "); // str == "rock and" str.append(" roll"); // str == "rock and roll" str.replace(5, 3, "&"); // str == "rock & roll"
In the above example the replace () function's first two arguments are the position from which to start replacing and the number of characters that should be replaced.
When data-modifying functions increase the size of the string, they may lead to reallocation of memory for the QString object. When this happens, QString expands by more than it immediately needs so as to have space for further expansion without reallocation until the size of the string has greatly increased.
The insert (), remove () and, when replacing a sub-string with one of different size, replace () functions can be slow ( 线性时间 ) for large strings, because they require moving many characters in the string by at least one position in memory.
If you are building a QString gradually and know in advance approximately how many characters the QString will contain, you can call reserve (), asking QString to preallocate a certain amount of memory. You can also call capacity () to find out how much memory the QString actually has allocated.
QString provides STL 样式迭代器 ( QString::const_iterator and QString::iterator ). In practice, iterators are handy when working with generic algorithms provided by the C++ standard library.
注意:
Iterators over a QString, and references to individual characters within one, cannot be relied on to remain valid when any non-
const
method of the QString is called. Accessing such an iterator or reference after the call to a non-
const
method leads to undefined behavior. When stability for iterator-like functionality is required, you should use indexes instead of iterators as they are not tied to QString's internal state and thus do not get invalidated.
注意:
Due to
隐式共享
, the first non-
const
operator or function used on a given QString may cause it to, internally, perform a deep copy of its data. This invalidates all iterators over the string and references to individual characters within it. After the first non-
const
operator, operations that modify QString may completely (in case of reallocation) or partially invalidate iterators and references, but other methods (such as
begin
() 或
end
()) will not. Accessing an iterator or reference after it has been invalidated leads to undefined behavior.
A frequent requirement is to remove whitespace characters from a string ('\n', '\t', ' ', etc.). If you want to remove whitespace from both ends of a QString, use the trimmed () function. If you want to remove whitespace from both ends and replace multiple consecutive whitespaces with a single space character within the string, use simplified ().
If you want to find all occurrences of a particular character or substring in a QString, use the indexOf () 或 lastIndexOf () functions. The former searches forward starting from a given index position, the latter searches backward. Both return the index position of the character or substring if they find it; otherwise, they return -1. For example, here is a typical loop that finds all occurrences of a particular substring:
QString str = "We must be <b>bold</b>, very <b>bold</b>"; qsizetype j = 0; while ((j = str.indexOf("<b>", j)) != -1) { qDebug() << "Found <b> tag at index position" << j; ++j; }
QString provides many functions for converting numbers into strings and strings into numbers. See the arg () functions, the setNum () functions, the number () static functions, and the toInt (), toDouble (), and similar functions.
To get an upper- or lowercase version of a string use toUpper () 或 toLower ().
Lists of strings are handled by the QStringList class. You can split a string into a list of strings using the split () function, and join a list of strings into a single string with an optional separator using QStringList::join (). You can obtain a list of strings from a string list that contain a particular substring or that match a particular QRegularExpression 使用 QStringList::filter () 函数。
If you want to see if a QString starts or ends with a particular substring use startsWith () 或 endsWith (). If you simply want to check whether a QString contains a particular character or substring, use the contains () function. If you want to find out how many times a particular character or substring occurs in the string, use count().
To obtain a pointer to the actual character data, call
data
() 或
constData
(). These functions return a pointer to the beginning of the
QChar
data. The pointer is guaranteed to remain valid until a non-
const
function is called on the QString.
QStrings can be compared using overloaded operators such as operator< (), operator<= (), operator== (), operator>= (), and so on. Note that the comparison is based exclusively on the numeric Unicode values of the characters. It is very fast, but is not what a human would expect; the QString::localeAwareCompare () function is usually a better choice for sorting user-interface strings, when such a comparison is available.
On Unix-like platforms (including Linux, macOS and iOS), when Qt is linked with the ICU library (which it usually is), its locale-aware sorting is used. Otherwise, on macOS and iOS,
localeAwareCompare
() compares according the "Order for sorted lists" setting in the International preferences panel. On other Unix-like systems without ICU, the comparison falls back to the system library's
strcoll()
,
QString provides the following three functions that return a
const char *
version of the string as
QByteArray
:
toUtf8
(),
toLatin1
(),和
toLocal8Bit
().
To convert from one of these encodings, QString provides fromLatin1 (), fromUtf8 (),和 fromLocal8Bit (). Other encodings are supported through the QStringEncoder and QStringDecoder 类。
As mentioned above, QString provides a lot of functions and operators that make it easy to interoperate with
const char *
strings. But this functionality is a double-edged sword: It makes QString more convenient to use if all strings are US-ASCII or Latin-1, but there is always the risk that an implicit conversion from or to
const char *
is done using the wrong 8-bit encoding. To minimize these risks, you can turn off these implicit conversions by defining some of the following preprocessor symbols:
You then need to explicitly call fromUtf8 (), fromLatin1 (),或 fromLocal8Bit () to construct a QString from an 8-bit string, or use the lightweight QLatin1StringView class, for example:
QString url = "https://www.unicode.org/"_L1;
Similarly, you must call toLatin1 (), toUtf8 (),或 toLocal8Bit () explicitly to convert the QString to an 8-bit string.
Note for C Programmers |
---|
Due to C++'s type system and the fact that QString is
隐式共享
, QStrings may be treated like
int
s or other basic types. For example:
QString Widget::boolToString(bool b) { QString result; if (b) result = "True" ; else result = "False" ; return result; }
The
|
For historical reasons, QString distinguishes between a null string and an empty string. A
null
string is a string that is initialized using QString's default constructor or by passing (
const char *
)0 to the constructor. An
empty
string is any string with size 0. A null string is always empty, but an empty string isn't necessarily null:
QString().isNull(); // returns true QString().isEmpty(); // returns true QString("").isNull(); // returns false QString("").isEmpty(); // returns true QString("abc").isNull(); // returns false QString("abc").isEmpty(); // returns false
All functions except isNull () treat null strings the same as empty strings. For example, toUtf8 (). constData () returns a valid pointer ( not nullptr) to a '\0' character for a null string. We recommend that you always use the isEmpty () function and avoid isNull ().
当
QString::arg
()
'%'
format specifier includes the
'L'
locale qualifier, and the base is ten (its default), the default locale is used. This can be set using
QLocale::setDefault
(). For more refined control of localized string representations of numbers, see
QLocale::toString
(). All other number formatting done by QString follows the C locale's representation of numbers.
当
QString::arg
() applies left-padding to numbers, the fill character
'0'
is treated specially. If the number is negative, its minus sign will appear before the zero-padding. If the field is localized, the locale-appropriate zero character is used in place of
'0'
. For floating-point numbers, this special treatment only applies if the number is finite.
In member functions (e.g.,
arg
(),
number
()) that represent floating-point numbers (
float
or
double
) as strings, the form of display can be controlled by a choice of
format
and
precision
, whose meanings are as for
QLocale::toString
(double, char, int).
If the selected format includes an exponent, localized forms follow the locale's convention on digits in the exponent. For non-localized formatting, the exponent shows its sign and includes at least two digits, left-padding with zero if needed.
Many strings are known at compile time. But the trivial constructor QString("Hello"), will copy the contents of the string, treating the contents as Latin-1. To avoid this one can use the QStringLiteral macro to directly create the required data at compile time. Constructing a QString out of the literal does then not cause any overhead at runtime.
A slightly less efficient way is to use QLatin1StringView . This class wraps a C string literal, precalculates it length at compile time and can then be used for faster comparison with QStrings and conversion to QStrings than a regular C string literal.
Using the QString
'+'
operator, it is easy to construct a complex string from multiple substrings. You will often write code like this:
QString foo; QString type = "long"; foo = "vector<"_L1 + type + ">::iterator"_L1; if (foo.startsWith("(" + type + ") 0x")) ...
There is nothing wrong with either of these string constructions, but there are a few hidden inefficiencies. Beginning with Qt 4.6, you can eliminate them.
First, multiple uses of the
'+'
operator usually means multiple memory allocations. When concatenating
n
substrings, where
n > 2
, there can be as many as
n - 1
calls to the memory allocator.
In 4.6, an internal template class
QStringBuilder
has been added along with a few helper functions. This class is marked internal and does not appear in the documentation, because you aren't meant to instantiate it in your code. Its use will be automatic, as described below. The class is found in
src/corelib/tools/qstringbuilder.cpp
if you want to have a look at it.
QStringBuilder
uses expression templates and reimplements the
'%'
operator so that when you use
'%'
for string concatenation instead of
'+'
, multiple substring concatenations will be postponed until the final result is about to be assigned to a QString. At this point, the amount of memory required for the final result is known. The memory allocator is then called
once
to get the required space, and the substrings are copied into it one by one.
Additional efficiency is gained by inlining and reduced reference counting (the QString created from a
QStringBuilder
typically has a ref count of 1, whereas
QString::append
() needs an extra test).
There are two ways you can access this improved method of string construction. The straightforward way is to include
QStringBuilder
wherever you want to use it, and use the
'%'
operator instead of
'+'
when concatenating strings:
#include <QStringBuilder> QString hello("hello"); QStringView el = QStringView{ hello }.mid(2, 3); QLatin1StringView world("world"); QString message = hello % el % world % QChar('!');
A more global approach which is the most convenient but not entirely source compatible, is to this define in your .pro file:
和
'+'
will automatically be performed as the
QStringBuilder
'%'
everywhere.
The maximum size of QString depends on the architecture. Most 64-bit systems can allocate more than 2 GB of memory, with a typical limit of 2^63 bytes. The actual value also depends on the overhead required for managing the data block. As a result, you can expect the maximum size of 2 GB minus overhead on 32-bit platforms, and 2^63 bytes minus overhead on 64-bit platforms. The number of elements that can be stored in a QString is this maximum size divided by the size of QChar .
When memory allocation fails, QString throws a
std::bad_alloc
exception if the application was compiled with exception support. Out of memory conditions in Qt containers are the only case where Qt will throw exceptions. If exceptions are disabled, then running out of memory is undefined behavior.
Note that the operating system may impose further limits on applications holding a lot of allocated memory, especially large, contiguous blocks. Such considerations, the configuration of such behavior or any mitigation are outside the scope of the Qt API.
另请参阅 fromRawData (), QChar , QStringView , QLatin1StringView ,和 QByteArray .
Qt 样式同义词 QString::const_iterator .
Qt 样式同义词 QString::iterator .
此枚举描述 Unicode 文本的各种规范化形式。
常量 | 值 | 描述 |
---|---|---|
QString::NormalizationForm_D
|
0
|
典型分解 |
QString::NormalizationForm_C
|
1
|
典型分解,紧接着是典型合成 |
QString::NormalizationForm_KD
|
2
|
兼容性分解 |
QString::NormalizationForm_KC
|
3
|
兼容性分解,紧接着是典型合成 |
另请参阅 normalized () 和 Unicode 标准附录 #15 .
This enum specifies flags that can be used to affect various aspects of the section () function's behavior with respect to separators and empty fields.
常量 | 值 | 描述 |
---|---|---|
QString::SectionDefault
|
0x00
|
Empty fields are counted, leading and trailing separators are not included, and the separator is compared case sensitively. |
QString::SectionSkipEmpty
|
0x01
|
Treat empty fields as if they don't exist, i.e. they are not considered as far as start and end are concerned. |
QString::SectionIncludeLeadingSep
|
0x02
|
Include the leading separator (if any) in the result string. |
QString::SectionIncludeTrailingSep
|
0x04
|
Include the trailing separator (if any) in the result string. |
QString::SectionCaseInsensitiveSeps
|
0x08
|
Compare the separator case-insensitively. |
The SectionFlags type is a typedef for QFlags <SectionFlag>. It stores an OR combination of SectionFlag values.
另请参阅 section ().
另请参阅 QString::iterator .
The QString::const_pointer typedef provides an STL-style const pointer to a QString 元素 ( QChar ).
另请参阅 QString::reverse_iterator and QString::const_iterator .
另请参阅 QString::const_iterator .
The QString::pointer typedef provides an STL-style pointer to a QString 元素 ( QChar ).
另请参阅 QString::const_reverse_iterator and QString::iterator .
Replaces occurrences of
%N
in this string with the corresponding argument from
args
. The arguments are not positional: the first of the
args
replaces the
%N
with the lowest
N
(all of them), the second of the
args
the
%N
with the next-lowest
N
etc.
Args
can consist of anything that implicitly converts to
QString
,
QStringView
or
QLatin1StringView
.
In addition, the following types are also supported: QChar , QLatin1Char .
另请参阅 QString::arg ().
[since 6.0]
template <typename Needle, typename Flags>
decltype
(
qTokenize
(
std::move
(*
this
),
std::forward
<
Needle
>(
needle
),
flags
...)) QString::
tokenize
(
Needle
&&
sep
,
Flags
...
flags
) &&
[since 6.0]
template <typename Needle, typename Flags>
decltype
(
qTokenize
(*
this
,
std::forward
<
Needle
>(
needle
),
flags
...)) QString::
tokenize
(
Needle
&&
sep
,
Flags
...
flags
) const &
[since 6.0]
template <typename Needle, typename Flags>
decltype
(
qTokenize
(
std::move
(*
this
),
std::forward
<
Needle
>(
needle
),
flags
...)) QString::
tokenize
(
Needle
&&
sep
,
Flags
...
flags
) const &&
Splits the string into substring views wherever sep occurs, and returns a lazy sequence of those strings.
相当于
return QStringTokenizer{std::forward<Needle>(sep), flags...};
except it works without C++17 Class Template Argument Deduction (CTAD) enabled in the compiler.
见 QStringTokenizer for how sep and flags interact to form the result.
注意: While this function returns QStringTokenizer , you should never, ever, name its template arguments explicitly. If you can use C++17 Class Template Argument Deduction (CTAD), you may write
QStringTokenizer result = sv.tokenize(sep);
(without template arguments). If you can't use C++17 CTAD, you must store the return value only in
auto
variables:
auto result = sv.tokenize(sep);
This is because the template arguments of QStringTokenizer have a very subtle dependency on the specific tokenize () overload from which they are returned, and they don't usually correspond to the type used for the separator.
该函数在 Qt 6.0 引入。
另请参阅 QStringTokenizer and qTokenize ().
[constexpr]
QString::
QString
()
Constructs a null string. Null strings are also considered empty.
另请参阅 isEmpty (), isNull (),和 Null 和空字符串之间的区别 .
[explicit]
QString::
QString
(const
QChar
*
unicode
,
qsizetype
size
= -1)
Constructs a string initialized with the first size characters of the QChar array unicode .
若 unicode is 0, a null string is constructed.
若 size is negative, unicode is assumed to point to a \0'-terminated array and its length is determined dynamically. The terminating null character is not considered part of the string.
QString makes a deep copy of the string data. The unicode data is copied as is and the Byte Order Mark is preserved if present.
另请参阅 fromRawData ().
Constructs a string of size 1 containing the character ch .
Constructs a string of the given size with every character set to ch .
另请参阅 fill ().
Constructs a copy of the Latin-1 string viewed by str .
另请参阅 fromLatin1 ().
[since 6.1]
QString::
QString
(const
char8_t
*
str
)
Constructs a string initialized with the UTF-8 string str . The given const char8_t pointer is converted to Unicode using the fromUtf8 () 函数。
该函数在 Qt 6.1 引入。
另请参阅 fromLatin1 (), fromLocal8Bit (),和 fromUtf8 ().
Constructs a string initialized with the 8-bit string str . The given const char pointer is converted to Unicode using the fromUtf8 () 函数。
You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
注意:
Defining
QT_RESTRICTED_CAST_FROM_ASCII
also disables this constructor, but enables a
QString(const char (&ch)[N])
constructor instead. Using non-literal input, or input with embedded NUL characters, or non-7-bit characters is undefined in this case.
另请参阅 fromLatin1 (), fromLocal8Bit (),和 fromUtf8 ().
Constructs a string initialized with the byte array ba . The given byte array is converted to Unicode using fromUtf8 ().
You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
注意: : any null ('\0') bytes in the byte array will be included in this string, converted to Unicode null characters (U+0000). This behavior is different from Qt 5.x.
另请参阅 fromLatin1 (), fromLocal8Bit (),和 fromUtf8 ().
构造副本为 other .
此操作花费 常量时间 , because QString is 隐式共享 . This makes returning a QString from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and that takes 线性时间 .
另请参阅 operator= ().
Move-constructs a QString instance, making it point at the same object that other 所指向的。
销毁字符串。
追加字符串 str onto the end of this string.
范例:
QString x = "free"; QString y = "dom"; x.append(y); // x == "freedom"
这如同使用 insert () 函数:
x.insert(x.size(), y);
append() 函数通常非常快 ( 常量时间 ),因为 QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.
另请参阅 operator+= (), prepend (),和 insert ().
此函数重载 append()。
追加字符 ch 到此字符串。
此函数重载 append()。
追加 len characters from the QChar array str 到此字符串。
[since 6.0]
QString
&QString::
append
(
QStringView
v
)
此函数重载 append()。
Appends the given string view v to this string and returns the result.
该函数在 Qt 6.0 引入。
此函数重载 append()。
Appends the Latin-1 string viewed by str 到此字符串。
[since 6.5]
QString
&QString::
append
(
QUtf8StringView
str
)
此函数重载 append()。
Appends the UTF-8 string view str 到此字符串。
该函数在 Qt 6.5 引入。
此函数重载 append()。
追加字符串 str to this string. The given const char pointer is converted to Unicode using the fromUtf8 () 函数。
可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
此函数重载 append()。
追加字节数组 ba to this string. The given byte array is converted to Unicode using the fromUtf8 () 函数。
可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
返回字符串副本,替换最小编号位置标记为字符串
a
,即:
%1
,
%2
, ...,
%99
.
fieldWidth specifies the minimum amount of space that argument a shall occupy. If a requires less space than fieldWidth , it is padded to fieldWidth with character fillChar . A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.
此范例展示如何创建
status
字符串为处理文件列表时报告进度:
QString i; // current file's number QString total; // number of files to process QString fileName; // current file's name QString status = QString("Processing file %1 of %2: %3") .arg(i).arg(total).arg(fileName);
首先,
arg(i)
替换
%1
。然后
arg(total)
替换
%2
。最后,
arg(fileName)
替换
%3
.
One advantage of using arg() over
asprintf
() is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest numbered unreplaced place marker, no matter where it appears. Also, if place marker
%i
appears more than once in the string, the arg() replaces all of them.
If there is no unreplaced place marker remaining, a warning message is output and the result is undefined. Place marker numbers must be in the range 1 to 99.
此函数重载 arg()。
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
另请参阅 Number Formats .
此函数重载 arg()。
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a into a string. base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
另请参阅 Number Formats .
此函数重载 arg()。
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.
The a argument is expressed in the given base , which is 10 by default and must be between 2 and 36.
The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a . The conversion uses the default locale. The default locale is determined from the system's locale settings at application startup. It can be changed using QLocale::setDefault (). The 'L' flag is ignored if base is not 10.
QString str; str = QString("Decimal 63 is %1 in hexadecimal") .arg(63, 0, 16); // str == "Decimal 63 is 3f in hexadecimal" QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates)); str = QString("%1 %L2 %L3") .arg(12345) .arg(12345) .arg(12345, 0, 16); // str == "12345 12,345 3039"
另请参阅 Number Formats .
此函数重载 arg()。
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a to a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
另请参阅 Number Formats .
此函数重载 arg()。
The a argument is expressed in base base , which is 10 by default and must be between 2 and 36. For bases other than 10, a is treated as an unsigned integer.
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.
The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a . The conversion uses the default locale, set by QLocale::setDefault (). If no default locale was specified, the system locale is used. The 'L' flag is ignored if base is not 10.
QString str; str = QString("Decimal 63 is %1 in hexadecimal") .arg(63, 0, 16); // str == "Decimal 63 is 3f in hexadecimal" QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates)); str = QString("%1 %L2 %L3") .arg(12345) .arg(12345) .arg(12345, 0, 16); // str == "12345 12,345 3039"
另请参阅 Number Formats .
此函数重载 arg()。
The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36.
另请参阅 Number Formats .
此函数重载 arg()。
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
另请参阅 Number Formats .
此函数重载 arg()。
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.
The base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.
另请参阅 Number Formats .
此函数重载 arg()。
Argument a is formatted according to the specified format and precision 。见 Floating-point Formats 了解细节。
fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.
double d = 12.34; QString str = QString("delta: %1").arg(d, 0, 'E', 3); // str == "delta: 1.234E+01"
另请参阅 QLocale::toString (), QLocale::FloatingPointPrecisionOption ,和 Number Formats .
此函数重载 arg()。
The a argument is interpreted as a Latin-1 character.
此函数重载 arg()。
这是重载函数。
Returns a copy of this string with the lowest-numbered place-marker replaced by string
a
,即:
%1
,
%2
, ...,
%99
.
fieldWidth specifies the minimum amount of space that a shall occupy. If a requires less space than fieldWidth , it is padded to fieldWidth with character fillChar . A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.
此范例展示如何创建
status
字符串为处理文件列表时报告进度:
int i; // current file's number int total; // number of files to process QStringView fileName; // current file's name QString status = QString("Processing file %1 of %2: %3") .arg(i).arg(total).arg(fileName);
首先,
arg(i)
替换
%1
。然后
arg(total)
替换
%2
。最后,
arg(fileName)
替换
%3
.
One advantage of using arg() over
asprintf
() is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest-numbered unreplaced place-marker, no matter where it appears. Also, if place-marker
%i
appears more than once in the string, arg() replaces all of them.
If there is no unreplaced place-marker remaining, a warning message is printed and the result is undefined. Place-marker numbers must be in the range 1 to 99.
这是重载函数。
Returns a copy of this string with the lowest-numbered place-marker replaced by the Latin-1 string viewed by
a
,即:
%1
,
%2
, ...,
%99
.
fieldWidth specifies the minimum amount of space that a shall occupy. If a requires less space than fieldWidth , it is padded to fieldWidth with character fillChar . A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.
One advantage of using arg() over
asprintf
() is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest-numbered unreplaced place-marker, no matter where it appears. Also, if place-marker
%i
appears more than once in the string, arg() replaces all of them.
If there is no unreplaced place-marker remaining, a warning message is printed and the result is undefined. Place-marker numbers must be in the range 1 to 99.
[static]
QString
QString::
asprintf
(const
char
*
cformat
, ...)
Safely builds a formatted string from the format string cformat and an arbitrary list of arguments.
The format string supports the conversion specifiers, length modifiers, and flags provided by printf() in the standard C++ library. The
cformat
string and
%s
arguments must be UTF-8 encoded.
注意:
The
%lc
escape sequence expects a unicode character of type
char16_t
,或
ushort
(as returned by
QChar::unicode
())。
%ls
escape sequence expects a pointer to a zero-terminated array of unicode characters of type
char16_t
, or ushort (as returned by
QString::utf16
()). This is at odds with the printf() in the standard C++ library, which defines
%lc
to print a wchar_t and
%ls
to print a
wchar_t*
, and might also produce compiler warnings on platforms where the size of
wchar_t
is not 16 bits.
警告: We do not recommend using QString::asprintf() in new Qt code. Instead, consider using QTextStream or arg (), both of which support Unicode strings seamlessly and are type-safe. Here is an example that uses QTextStream :
QString result; QTextStream(&result) << "pi = " << 3.14; // result == "pi = 3.14"
For translations , especially if the strings contains more than one escape sequence, you should consider using the arg () function instead. This allows the order of the replacements to be controlled by the translator.
另请参阅 arg ().
Returns the character at the given index position in the string.
The position must be a valid index position in the string (i.e., 0 <= position < size ()).
另请参阅 operator[] ().
Returns the last character in the string. Same as
at(size() - 1)
.
This function is provided for STL compatibility.
警告: Calling this function on an empty string constitutes undefined behavior.
另请参阅 front (), at (),和 operator[] ().
Returns a reference to the last character in the string. Same as
operator[](size() - 1)
.
This function is provided for STL compatibility.
警告: Calling this function on an empty string constitutes undefined behavior.
另请参阅 front (), at (),和 operator[] ().
返回 STL 样式迭代器 pointing to the first character in the string.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
另请参阅 constBegin () 和 end ().
此函数重载 begin()。
Returns the maximum number of characters that can be stored in the string without forcing a reallocation.
The sole purpose of this function is to provide a means of fine tuning QString 's memory usage. In general, you will rarely ever need to call this function. If you want to know how many characters are in the string, call size ().
注意: a statically allocated string will report a capacity of 0, even if it's not empty.
注意: The free space position in the allocated memory block is undefined. In other words, one should not assume that the free memory is always located after the initialized elements.
返回常量 STL 样式迭代器 pointing to the first character in the string.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
返回常量 STL 样式迭代器 pointing just after the last character in the string.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
移除 n characters from the end of the string.
若 n is greater than or equal to size (), the result is an empty string; if n is negative, it is equivalent to passing zero.
范例:
QString str("LOGOUT\r\n"); str.chop(2); // str == "LOGOUT"
If you want to remove characters from the beginning of the string, use remove () 代替。
另请参阅 truncate (), resize (), remove (),和 QStringView::chop ().
Returns a string that contains the size () - len leftmost characters of this string.
注意: The behavior is undefined if len is negative or greater than size ().
另请参阅 endsWith (), first (), last (), sliced (), chop (),和 truncate ().
Clears the contents of the string and makes it null.
[static]
int
QString::
compare
(const
QString
&
s1
, const
QString
&
s2
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive)
比较 s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .
若 cs is Qt::CaseSensitive (the default), the comparison is case-sensitive; otherwise the comparison is case-insensitive.
Case sensitive comparison is based exclusively on the numeric Unicode values of the characters and is very fast, but is not what a human would expect. Consider sorting user-visible strings with localeAwareCompare ().
int x = QString::compare("aUtO", "AuTo", Qt::CaseInsensitive); // x == 0 int y = QString::compare("auto", "Car", Qt::CaseSensitive); // y > 0 int z = QString::compare("auto", "Car", Qt::CaseInsensitive); // z < 0
注意: This function treats null strings the same as empty strings, for more details see Null 和空字符串之间的区别 .
另请参阅 operator== (), operator< (), operator> (),和 Comparing Strings .
This function overloads compare().
Lexically compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other string.
Same as compare(*this, other , cs ).
This function overloads compare().
Same as compare(*this, other , cs ).
This function overloads compare().
Performs a comparison of this with s , using the case sensitivity setting cs .
This function overloads compare().
Performs a comparison of this with ch , using the case sensitivity setting cs .
[static]
int
QString::
compare
(const
QString
&
s1
,
QLatin1StringView
s2
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive)
This function overloads compare().
Performs a comparison of s1 and s2 , using the case sensitivity setting cs .
[static]
int
QString::
compare
(
QLatin1StringView
s1
, const
QString
&
s2
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive)
This function overloads compare().
Performs a comparison of s1 and s2 , using the case sensitivity setting cs .
[static]
int
QString::
compare
(const
QString
&
s1
,
QStringView
s2
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive)
This function overloads compare().
[static]
int
QString::
compare
(
QStringView
s1
, const
QString
&
s2
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive)
This function overloads compare().
返回常量 STL 样式迭代器 pointing to the first character in the string.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
Returns a pointer to the data stored in the QString . The pointer can be used to access the characters that compose the string.
Note that the pointer remains valid only as long as the string is not modified.
注意: The returned string may not be '\0'-terminated. Use size () to determine the length of the array.
另请参阅 data (), operator[] (),和 fromRawData ().
返回常量 STL 样式迭代器 pointing just after the last character in the string.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
另请参阅 constBegin () 和 end ().
返回
true
if this string contains an occurrence of the string
str
;否则返回
false
.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString str = "Peter Pan"; str.contains("peter", Qt::CaseInsensitive); // returns true
This function overloads contains().
返回
true
if this string contains an occurrence of the character
ch
;否则返回
false
.
This function overloads contains().
返回
true
if this string contains an occurrence of the latin-1 string
str
;否则返回
false
.
This function overloads contains().
返回
true
if this string contains an occurrence of the string view
str
;否则返回
false
.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
返回
true
if the regular expression
re
matches somewhere in this string; otherwise returns
false
.
If the match is successful and
rmatch
不是
nullptr
, it also writes the results of the match into the
QRegularExpressionMatch
object pointed to by
rmatch
.
另请参阅 QRegularExpression::match ().
Returns the number of (potentially overlapping) occurrences of the string str in this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
另请参阅 contains () 和 indexOf ().
This function overloads count().
Returns the number of occurrences of character ch in the string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
另请参阅 contains () 和 indexOf ().
[since 6.0]
qsizetype
QString::
count
(
QStringView
str
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive) const
This function overloads count().
Returns the number of (potentially overlapping) occurrences of the string view str in this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
该函数在 Qt 6.0 引入。
另请参阅 contains () 和 indexOf ().
This function overloads count().
Returns the number of times the regular expression re matches in the string.
For historical reasons, this function counts overlapping matches, so in the example below, there are four instances of "ana" or "ama":
QString str = "banana and panama"; str.count(QRegularExpression("a[nm]a")); // returns 4
This behavior is different from simply iterating over the matches in the string using QRegularExpressionMatchIterator .
另请参阅 QRegularExpression::globalMatch ().
返回常量 STL-style reverse iterator pointing to the first character in the string, in reverse order.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
另请参阅 begin (), rbegin (),和 rend ().
返回常量 STL-style reverse iterator pointing just after the last character in the string, in reverse order.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
另请参阅 end (), rend (),和 rbegin ().
Returns a pointer to the data stored in the QString . The pointer can be used to access and modify the characters that compose the string.
不像 constData () 和 unicode (), the returned data is always '\0'-terminated.
范例:
QString str = "Hello world"; QChar *data = str.data(); while (!data->isNull()) { qDebug() << data->unicode(); ++data; }
Note that the pointer remains valid only as long as the string is not modified by other means. For read-only access, constData () 更快,因为它从不导致 深拷贝 的出现。
另请参阅 constData () 和 operator[] ().
这是重载函数。
注意: The returned string may not be '\0'-terminated. Use size () to determine the length of the array.
另请参阅 fromRawData ().
返回 STL 样式迭代器 pointing just after the last character in the string.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
此函数重载 end()。
返回
true
if the string ends with
s
;否则返回
false
.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
QString str = "Bananas"; str.endsWith("anas"); // returns true str.endsWith("pple"); // returns false
另请参阅 startsWith ().
This function overloads endsWith().
返回
true
if the string ends with the string view
str
;否则返回
false
.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
另请参阅 startsWith ().
This function overloads endsWith().
返回
true
if the string ends with
c
;否则返回
false
.
This function overloads endsWith().
[since 6.1]
QString::iterator
QString::
erase
(
QString::const_iterator
first
,
QString::const_iterator
last
)
Removes from the string the characters in the half-open range [ first , last ). Returns an iterator to the character immediately after the last erased character (i.e. the character referred to by last before the erase).
该函数在 Qt 6.1 引入。
[since 6.5]
QString::iterator
QString::
erase
(
QString::const_iterator
it
)
Removes the character denoted by
it
from the string. Returns an iterator to the character immediately after the erased character.
QString c = "abcdefg"; auto it = c.erase(c.cbegin()); // c is now "bcdefg"; "it" points to "b"
该函数在 Qt 6.5 引入。
Sets every character in the string to character ch 。若 size is different from -1 (default), the string is resized to size beforehand.
范例:
QString str = "Berlin"; str.fill('z'); // str == "zzzzzz" str.fill('A', 2); // str == "AA"
另请参阅 resize ().
[since 6.0]
QString
QString::
first
(
qsizetype
n
) const
Returns a string that contains the first n characters of this string.
注意: The behavior is undefined when n < 0 or n > size ().
QString x = "Pineapple"; QString y = x.first(4); // y == "Pine"
该函数在 Qt 6.0 引入。
另请参阅 last (), sliced (), startsWith (), chopped (), chop (),和 truncate ().
[static]
QString
QString::
fromCFString
(
CFStringRef
string
)
构造新的 QString containing a copy of the string CFString.
注意: this function is only available on macOS and iOS.
[static]
QString
QString::
fromLatin1
(const
char
*
str
,
qsizetype
size
)
返回 QString initialized with the first size characters of the Latin-1 string str .
若
size
is
-1
,
strlen(str)
is used instead.
另请参阅 toLatin1 (), fromUtf8 (),和 fromLocal8Bit ().
[static, since 6.0]
QString
QString::
fromLatin1
(
QByteArrayView
str
)
这是重载函数。
返回 QString initialized with the Latin-1 string str .
注意: : any null ('\0') bytes in the byte array will be included in this string, converted to Unicode null characters (U+0000).
该函数在 Qt 6.0 引入。
[static]
QString
QString::
fromLatin1
(const
QByteArray
&
str
)
这是重载函数。
返回 QString initialized with the Latin-1 string str .
注意: : any null ('\0') bytes in the byte array will be included in this string, converted to Unicode null characters (U+0000). This behavior is different from Qt 5.x.
[static]
QString
QString::
fromLocal8Bit
(const
char
*
str
,
qsizetype
size
)
返回 QString initialized with the first size characters of the 8-bit string str .
若
size
is
-1
,
strlen(str)
is used instead.
On Unix systems this is equivalent to fromUtf8 (), on Windows the systems current code page is being used.
另请参阅 toLocal8Bit (), fromLatin1 (),和 fromUtf8 ().
[static, since 6.0]
QString
QString::
fromLocal8Bit
(
QByteArrayView
str
)
这是重载函数。
返回 QString initialized with the 8-bit string str .
注意: : any null ('\0') bytes in the byte array will be included in this string, converted to Unicode null characters (U+0000).
该函数在 Qt 6.0 引入。
[static]
QString
QString::
fromLocal8Bit
(const
QByteArray
&
str
)
这是重载函数。
返回 QString initialized with the 8-bit string str .
注意: : any null ('\0') bytes in the byte array will be included in this string, converted to Unicode null characters (U+0000). This behavior is different from Qt 5.x.
[static]
QString
QString::
fromNSString
(const
NSString
*
string
)
构造新的 QString containing a copy of the string NSString.
注意: this function is only available on macOS and iOS.
[static]
QString
QString::
fromRawData
(const
QChar
*
unicode
,
qsizetype
size
)
构造 QString that uses the first size Unicode characters in the array unicode . The data in unicode is not copied. The caller must be able to guarantee that unicode will not be deleted or modified as long as the QString (or an unmodified copy of it) exists.
Any attempts to modify the QString or copies of it will cause it to create a deep copy of the data, ensuring that the raw data isn't modified.
Here is an example of how we can use a QRegularExpression on raw data in memory without requiring to copy the data into a QString :
QRegularExpression pattern("\u00A4"); static const QChar unicode[] = { 0x005A, 0x007F, 0x00A4, 0x0060, 0x1009, 0x0020, 0x0020}; qsizetype size = sizeof(unicode) / sizeof(QChar); QString str = QString::fromRawData(unicode, size); if (str.contains(pattern) { // ... }
警告: A string created with fromRawData() is not '\0'-terminated, unless the raw data contains a '\0' character at position size . This means unicode () will not return a '\0'-terminated string (although utf16 () does, at the cost of copying the raw data).
另请参阅 fromUtf16 () 和 setRawData ().
[static]
QString
QString::
fromStdString
(const
std::string
&
str
)
返回副本为 str string. The given string is converted to Unicode using the fromUtf8 () 函数。
另请参阅 fromLatin1 (), fromLocal8Bit (), fromUtf8 (),和 QByteArray::fromStdString ().
[static]
QString
QString::
fromStdU16String
(const
std::u16string
&
str
)
返回副本为 str string. The given string is assumed to be encoded in UTF-16.
另请参阅 fromUtf16 (), fromStdWString (),和 fromStdU32String ().
[static]
QString
QString::
fromStdU32String
(const
std::u32string
&
str
)
返回副本为 str string. The given string is assumed to be encoded in UCS-4.
另请参阅 fromUcs4 (), fromStdWString (),和 fromStdU16String ().
[static]
QString
QString::
fromStdWString
(const
std::wstring
&
str
)
返回副本为 str string. The given string is assumed to be encoded in utf16 if the size of wchar_t is 2 bytes (e.g. on windows) and ucs4 if the size of wchar_t is 4 bytes (most Unix systems).
另请参阅 fromUtf16 (), fromLatin1 (), fromLocal8Bit (), fromUtf8 (), fromUcs4 (), fromStdU16String (),和 fromStdU32String ().
[static]
QString
QString::
fromUcs4
(const
char32_t
*
unicode
,
qsizetype
size
= -1)
返回 QString initialized with the first size characters of the Unicode string unicode (ISO-10646-UCS-4 encoded).
若 size is -1 (default), unicode must be \0'-terminated.
另请参阅 toUcs4 (), fromUtf16 (), utf16 (), setUtf16 (), fromWCharArray (),和 fromStdU32String ().
[static]
QString
QString::
fromUtf8
(const
char
*
str
,
qsizetype
size
)
返回 QString initialized with the first size bytes of the UTF-8 string str .
若
size
is
-1
,
strlen(str)
is used instead.
UTF-8 is a Unicode codec and can represent all characters in a Unicode string like QString . However, invalid sequences are possible with UTF-8 and, if any such are found, they will be replaced with one or more "replacement characters", or suppressed. These include non-Unicode sequences, non-characters, overlong sequences or surrogate codepoints encoded into UTF-8.
This function can be used to process incoming data incrementally as long as all UTF-8 characters are terminated within the incoming data. Any unterminated characters at the end of the string will be replaced or suppressed. In order to do stateful decoding, please use QStringDecoder .
另请参阅 toUtf8 (), fromLatin1 (),和 fromLocal8Bit ().
[static, since 6.0]
QString
QString::
fromUtf8
(
QByteArrayView
str
)
这是重载函数。
返回 QString initialized with the UTF-8 string str .
注意: : any null ('\0') bytes in the byte array will be included in this string, converted to Unicode null characters (U+0000).
该函数在 Qt 6.0 引入。
[static]
QString
QString::
fromUtf8
(const
QByteArray
&
str
)
这是重载函数。
返回 QString initialized with the UTF-8 string str .
注意: : any null ('\0') bytes in the byte array will be included in this string, converted to Unicode null characters (U+0000). This behavior is different from Qt 5.x.
[static, since 6.1]
QString
QString::
fromUtf8
(const
char8_t
*
str
)
这是重载函数。
This overload is only available when compiling in C++20 mode.
该函数在 Qt 6.1 引入。
[static, since 6.0]
QString
QString::
fromUtf8
(const
char8_t
*
str
,
qsizetype
size
)
这是重载函数。
This overload is only available when compiling in C++20 mode.
该函数在 Qt 6.0 引入。
[static]
QString
QString::
fromUtf16
(const
char16_t
*
unicode
,
qsizetype
size
= -1)
返回 QString initialized with the first size characters of the Unicode string unicode (ISO-10646-UTF-16 encoded).
若 size is -1 (default), unicode must be \0'-terminated.
This function checks for a Byte Order Mark (BOM). If it is missing, host byte order is assumed.
This function is slow compared to the other Unicode conversions. Use QString (const QChar *, qsizetype) or QString (const QChar *) if possible.
QString makes a deep copy of the Unicode data.
另请参阅 utf16 (), setUtf16 (),和 fromStdU16String ().
[static]
QString
QString::
fromWCharArray
(const
wchar_t
*
string
,
qsizetype
size
= -1)
返回副本为 string , where the encoding of string depends on the size of wchar. If wchar is 4 bytes, the string is interpreted as UCS-4, if wchar is 2 bytes it is interpreted as UTF-16.
若 size is -1 (default), the string must be '\0'-terminated.
另请参阅 fromUtf16 (), fromLatin1 (), fromLocal8Bit (), fromUtf8 (), fromUcs4 (),和 fromStdWString ().
Returns the first character in the string. Same as
at(0)
.
This function is provided for STL compatibility.
警告: Calling this function on an empty string constitutes undefined behavior.
另请参阅 back (), at (),和 operator[] ().
Returns a reference to the first character in the string. Same as
operator[](0)
.
This function is provided for STL compatibility.
警告: Calling this function on an empty string constitutes undefined behavior.
另请参阅 back (), at (),和 operator[] ().
Returns the index position of the first occurrence of the Latin-1 string viewed by str in this string, searching forward from index position from . Returns -1 if str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString x = "sticky question"; QString y = "sti"; x.indexOf(y); // returns 0 x.indexOf(y, 1); // returns 10 x.indexOf(y, 10); // returns 10 x.indexOf(y, 11); // returns -1
若 from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
另请参阅 lastIndexOf (), contains (),和 count ().
此函数重载 indexOf()。
Returns the index position of the first occurrence of the character ch in this string, searching forward from index position from . Returns -1 if ch 找不到。
Returns the index position of the first occurrence of the string str in this string, searching forward from index position from . Returns -1 if str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString x = "sticky question"; QString y = "sti"; x.indexOf(y); // returns 0 x.indexOf(y, 1); // returns 10 x.indexOf(y, 10); // returns 10 x.indexOf(y, 11); // returns -1
若 from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
另请参阅 lastIndexOf (), contains (),和 count ().
此函数重载 indexOf()。
Returns the index position of the first occurrence of the string view str in this string, searching forward from index position from . Returns -1 if str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
若 from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
另请参阅 QStringView::indexOf (), lastIndexOf (), contains (),和 count ().
Returns the index position of the first match of the regular expression re in the string, searching forward from index position from . Returns -1 if re didn't match anywhere.
If the match is successful and
rmatch
不是
nullptr
, it also writes the results of the match into the
QRegularExpressionMatch
object pointed to by
rmatch
.
范例:
QString str = "the minimum"; str.indexOf(QRegularExpression("m[aeiou]"), 0); // returns 4 QString str = "the minimum"; QRegularExpressionMatch match; str.indexOf(QRegularExpression("m[aeiou]"), 0, &match); // returns 4 // match.captured() == mi
插入字符串 str at the given index position and returns a reference to this string.
范例:
QString str = "Meal"; str.insert(1, QString("ontr")); // str == "Montreal"
This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by str .
另请参阅 append (), prepend (), replace (),和 remove ().
This function overloads insert().
插入 ch at the given index position in the string.
This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by ch .
This function overloads insert().
Inserts the first size characters of the QChar array unicode at the given index position in the string.
This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by size characters of the QChar array unicode .
[since 6.0]
QString
&QString::
insert
(
qsizetype
position
,
QStringView
str
)
This function overloads insert().
Inserts the string view str at the given index position and returns a reference to this string.
This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by str .
该函数在 Qt 6.0 引入。
This function overloads insert().
Inserts the Latin-1 string viewed by str at the given index position .
This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by str .
[since 6.5]
QString
&QString::
insert
(
qsizetype
position
,
QUtf8StringView
str
)
This function overloads insert().
Inserts the UTF-8 string view str at the given index position .
注意: Inserting variable-width UTF-8-encoded string data is conceptually slower than inserting fixed-width string data such as UTF-16 ( QStringView ) or Latin-1 ( QLatin1StringView ) and should thus be used sparingly.
This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by str .
该函数在 Qt 6.5 引入。
This function overloads insert().
Inserts the C string str at the given index position and returns a reference to this string.
This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by str .
This function is not available when QT_NO_CAST_FROM_ASCII is defined.
This function overloads insert().
Interprets the contents of str as UTF-8, inserts the Unicode string it encodes at the given index position and returns a reference to this string.
This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by str .
This function is not available when QT_NO_CAST_FROM_ASCII is defined.
返回
true
if the string has no characters; otherwise returns
false
.
范例:
QString().isEmpty(); // returns true QString("").isEmpty(); // returns true QString("x").isEmpty(); // returns false QString("abc").isEmpty(); // returns false
另请参阅 size ().
返回
true
if the string is lowercase, that is, it's identical to its
toLower
() folding.
Note that this does not mean that the string does not contain uppercase letters (some uppercase letters do not have a lowercase folding; they are left unchanged by toLower ()). For more information, refer to the Unicode standard, section 3.13.
另请参阅 QChar::toLower () 和 isUpper ().
返回
true
if this string is null; otherwise returns
false
.
范例:
QString().isNull(); // returns true QString("").isNull(); // returns false QString("abc").isNull(); // returns false
Qt makes a distinction between null strings and empty strings for historical reasons. For most applications, what matters is whether or not a string contains any data, and this can be determined using the isEmpty () 函数。
另请参阅 isEmpty ().
返回
true
if the string is read right to left.
另请参阅 QStringView::isRightToLeft ().
返回
true
if the string is uppercase, that is, it's identical to its
toUpper
() folding.
Note that this does not mean that the string does not contain lowercase letters (some lowercase letters do not have a uppercase folding; they are left unchanged by toUpper ()). For more information, refer to the Unicode standard, section 3.13.
另请参阅 QChar::toUpper () 和 isLower ().
返回
true
if the string contains valid UTF-16 encoded data, or
false
否则。
Note that this function does not perform any special validation of the data; it merely checks if it can be successfully decoded from UTF-16. The data is assumed to be in host byte order; the presence of a BOM is meaningless.
另请参阅 QStringView::isValidUtf16 ().
[since 6.0]
QString
QString::
last
(
qsizetype
n
) const
Returns the string that contains the last n characters of this string.
注意: The behavior is undefined when n < 0 or n > size ().
QString x = "Pineapple"; QString y = x.last(5); // y == "apple"
该函数在 Qt 6.0 引入。
另请参阅 first (), sliced (), endsWith (), chopped (), chop (),和 truncate ().
Returns the index position of the last occurrence of the string str in this string, searching backward from index position from .
若 from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
返回 -1,若 str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString x = "crazy azimuths"; QString y = "az"; x.lastIndexOf(y); // returns 6 x.lastIndexOf(y, 6); // returns 6 x.lastIndexOf(y, 5); // returns 2 x.lastIndexOf(y, 1); // returns -1
注意:
When searching for a 0-length
str
, the match at the end of the data is excluded from the search by a negative
from
, even though
-1
is normally thought of as searching from the end of the string: the match at the end is
after
the last character, so it is excluded. To include such a final empty match, either give a positive value for
from
or omit the
from
parameter entirely.
另请参阅 indexOf (), contains (),和 count ().
[since 6.3]
qsizetype
QString::
lastIndexOf
(
QChar
c
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive) const
This function overloads lastIndexOf().
该函数在 Qt 6.3 引入。
This function overloads lastIndexOf().
Returns the index position of the last occurrence of the character ch in this string, searching backward from index position from .
[since 6.2]
qsizetype
QString::
lastIndexOf
(
QLatin1StringView
str
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive) const
This function overloads lastIndexOf().
Returns the index position of the last occurrence of the string str in this string. Returns -1 if str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString x = "crazy azimuths"; QString y = "az"; x.lastIndexOf(y); // returns 6 x.lastIndexOf(y, 6); // returns 6 x.lastIndexOf(y, 5); // returns 2 x.lastIndexOf(y, 1); // returns -1
该函数在 Qt 6.2 引入。
另请参阅 indexOf (), contains (),和 count ().
This function overloads lastIndexOf().
Returns the index position of the last occurrence of the Latin-1 string viewed by str in this string, searching backward from index position from .
若 from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
返回 -1,若 str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString x = "crazy azimuths"; QString y = "az"; x.lastIndexOf(y); // returns 6 x.lastIndexOf(y, 6); // returns 6 x.lastIndexOf(y, 5); // returns 2 x.lastIndexOf(y, 1); // returns -1
注意:
When searching for a 0-length
str
, the match at the end of the data is excluded from the search by a negative
from
, even though
-1
is normally thought of as searching from the end of the string: the match at the end is
after
the last character, so it is excluded. To include such a final empty match, either give a positive value for
from
or omit the
from
parameter entirely.
另请参阅 indexOf (), contains (),和 count ().
[since 6.2]
qsizetype
QString::
lastIndexOf
(const
QString
&
str
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive) const
This function overloads lastIndexOf().
Returns the index position of the last occurrence of the string str in this string. Returns -1 if str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString x = "crazy azimuths"; QString y = "az"; x.lastIndexOf(y); // returns 6 x.lastIndexOf(y, 6); // returns 6 x.lastIndexOf(y, 5); // returns 2 x.lastIndexOf(y, 1); // returns -1
该函数在 Qt 6.2 引入。
另请参阅 indexOf (), contains (),和 count ().
[since 6.2]
qsizetype
QString::
lastIndexOf
(
QStringView
str
,
Qt::CaseSensitivity
cs
= Qt::CaseSensitive) const
This function overloads lastIndexOf().
Returns the index position of the last occurrence of the string view str in this string. Returns -1 if str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
该函数在 Qt 6.2 引入。
另请参阅 indexOf (), contains (),和 count ().
This function overloads lastIndexOf().
Returns the index position of the last occurrence of the string view str in this string, searching backward from index position from .
若 from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
返回 -1,若 str 找不到。
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
注意:
When searching for a 0-length
str
, the match at the end of the data is excluded from the search by a negative
from
, even though
-1
is normally thought of as searching from the end of the string: the match at the end is
after
the last character, so it is excluded. To include such a final empty match, either give a positive value for
from
or omit the
from
parameter entirely.
另请参阅 indexOf (), contains (),和 count ().
[since 6.2]
qsizetype
QString::
lastIndexOf
(const
QRegularExpression
&
re
,
QRegularExpressionMatch
*
rmatch
= nullptr) const
This function overloads lastIndexOf().
Returns the index position of the last match of the regular expression re in the string. Returns -1 if re didn't match anywhere.
If the match is successful and
rmatch
不是
nullptr
, it also writes the results of the match into the
QRegularExpressionMatch
object pointed to by
rmatch
.
范例:
QString str = "the minimum"; str.lastIndexOf(QRegularExpression("m[aeiou]")); // returns 8 QString str = "the minimum"; QRegularExpressionMatch match; str.lastIndexOf(QRegularExpression("m[aeiou]"), -1, &match); // returns 8 // match.captured() == mu
注意: Due to how the regular expression matching algorithm works, this function will actually match repeatedly from the beginning of the string until the end of the string is reached.
该函数在 Qt 6.2 引入。
Returns the index position of the last match of the regular expression re in the string, which starts before the index position from .
若 from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.
返回 -1,若 re didn't match anywhere.
If the match is successful and
rmatch
不是
nullptr
, it also writes the results of the match into the
QRegularExpressionMatch
object pointed to by
rmatch
.
范例:
QString str = "the minimum"; str.lastIndexOf(QRegularExpression("m[aeiou]")); // returns 8 QString str = "the minimum"; QRegularExpressionMatch match; str.lastIndexOf(QRegularExpression("m[aeiou]"), -1, &match); // returns 8 // match.captured() == mu
注意: Due to how the regular expression matching algorithm works, this function will actually match repeatedly from the beginning of the string until the position from is reached.
注意:
When searching for a regular expression
re
that may match 0 characters, the match at the end of the data is excluded from the search by a negative
from
, even though
-1
is normally thought of as searching from the end of the string: the match at the end is
after
the last character, so it is excluded. To include such a final empty match, either give a positive value for
from
or omit the
from
parameter entirely.
Returns a substring that contains the n leftmost characters of the string.
If you know that n cannot be out of bounds, use first () instead in new code, because it is faster.
The entire string is returned if n is greater than or equal to size (), or less than zero.
另请参阅 first (), last (), startsWith (), chopped (), chop (),和 truncate ().
Returns a string of size width that contains this string padded by the fill character.
若
truncate
is
false
和
size
() of the string is more than
width
, then the returned string is a copy of the string.
QString s = "apple"; QString t = s.leftJustified(8, '.'); // t == "apple..."
若
truncate
is
true
和
size
() of the string is more than
width
, then any characters in a copy of the string after position
width
are removed, and the copy is returned.
QString str = "Pineapple"; str = str.leftJustified(5, '.', true); // str == "Pinea"
另请参阅 rightJustified ().
Returns the number of characters in this string. Equivalent to size ().
另请参阅 resize ().
[static]
int
QString::
localeAwareCompare
(const
QString
&
s1
, const
QString
&
s2
)
比较 s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .
The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.
另请参阅 compare (), QLocale ,和 Comparing Strings .
This function overloads localeAwareCompare().
Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other 字符串。
The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.
如同
localeAwareCompare(*this, other)
.
另请参阅 Comparing Strings .
[since 6.0]
int
QString::
localeAwareCompare
(
QStringView
other
) const
This function overloads localeAwareCompare().
Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other 字符串。
The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.
如同
localeAwareCompare(*this, other)
.
该函数在 Qt 6.0 引入。
另请参阅 Comparing Strings .
[static, since 6.0]
int
QString::
localeAwareCompare
(
QStringView
s1
,
QStringView
s2
)
This function overloads localeAwareCompare().
比较 s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .
The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.
该函数在 Qt 6.0 引入。
另请参阅 Comparing Strings .
Returns a string that contains n characters of this string, starting at the specified position 索引。
If you know that position and n cannot be out of bounds, use sliced () instead in new code, because it is faster.
Returns a null string if the position index exceeds the length of the string. If there are less than n characters available in the string starting at the given position ,或者若 n is -1 (default), the function returns all characters that are available from the specified position .
另请参阅 first (), last (), sliced (), chopped (), chop (),和 truncate ().
Returns the string in the given Unicode normalization mode , according to the given version of the Unicode standard.
[static]
QString
QString::
number
(
long
n
,
int
base
= 10)
Returns a string equivalent of the number n 根据指定 base .
The base is 10 by default and must be between 2 and 36. For bases other than 10, n is treated as an unsigned integer.
格式始终使用 QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.
long a = 63; QString s = QString::number(a, 16); // s == "3f" QString t = QString::number(a, 16).toUpper(); // t == "3F"
另请参阅 setNum ().
[static]
QString
QString::
number
(
int
n
,
int
base
= 10)
这是重载函数。
[static]
QString
QString::
number
(
uint
n
,
int
base
= 10)
这是重载函数。
[static]
QString
QString::
number
(
ulong
n
,
int
base
= 10)
这是重载函数。
[static]
QString
QString::
number
(
qlonglong
n
,
int
base
= 10)
这是重载函数。
[static]
QString
QString::
number
(
qulonglong
n
,
int
base
= 10)
这是重载函数。
[static]
QString
QString::
number
(
double
n
,
char
format
= 'g',
int
precision
= 6)
Returns a string representing the floating-point number n .
Returns a string that represents n , formatted according to the specified format and precision .
For formats with an exponent, the exponent will show its sign and have at least two digits, left-padding the exponent with zero if needed.
另请参阅 setNum (), QLocale::toString (), QLocale::FloatingPointPrecisionOption ,和 Number Formats .
前置字符串 str to the beginning of this string and returns a reference to this string.
This operation is typically very fast ( 常量时间 ),因为 QString preallocates extra space at the beginning of the string data, so it can grow without reallocating the entire string each time.
范例:
QString x = "ship"; QString y = "air"; x.prepend(y); // x == "airship"
This function overloads prepend().
前置字符 ch 到此字符串。
This function overloads prepend().
前置 len characters from the QChar array str to this string and returns a reference to this string.
[since 6.0]
QString
&QString::
prepend
(
QStringView
str
)
This function overloads prepend().
Prepends the string view str to the beginning of this string and returns a reference to this string.
该函数在 Qt 6.0 引入。
This function overloads prepend().
Prepends the Latin-1 string viewed by str 到此字符串。
[since 6.5]
QString
&QString::
prepend
(
QUtf8StringView
str
)
This function overloads prepend().
Prepends the UTF-8 string view str 到此字符串。
该函数在 Qt 6.5 引入。
This function overloads prepend().
前置字符串 str to this string. The const char pointer is converted to Unicode using the fromUtf8 () 函数。
可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads prepend().
前置字节数组 ba to this string. The byte array is converted to Unicode using the fromUtf8 () 函数。
可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function is provided for STL compatibility, appending the given
other
string onto the end of this string. It is equivalent to
append(other)
.
另请参阅 append ().
这是重载函数。
Appends the given ch character onto the end of this string.
This function is provided for STL compatibility, prepending the given
other
string to the beginning of this string. It is equivalent to
prepend(other)
.
另请参阅 prepend ().
这是重载函数。
Prepends the given ch character to the beginning of this string.
返回 STL-style reverse iterator pointing to the first character in the string, in reverse order.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
另请参阅 begin (), crbegin (),和 rend ().
这是重载函数。
移除 n characters from the string, starting at the given position index, and returns a reference to the string.
If the specified position index is within the string, but position + n is beyond the end of the string, the string is truncated at the specified position .
若 n is <= 0 nothing is changed.
QString s = "Montreal"; s.remove(1, 4); // s == "Meal"
Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze () after the last change to the string's size.
Removes every occurrence of the character ch in this string, and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString t = "Ali Baba"; t.remove(QChar('a'), Qt::CaseInsensitive); // t == "li Bb"
这如同
replace(ch, "", cs)
.
Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze () after the last change to the string's size.
另请参阅 replace ().
这是重载函数。
Removes every occurrence of the given Latin-1 string viewed by str from this string, and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
这如同
replace(str, "", cs)
.
Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze () after the last change to the string's size.
另请参阅 replace ().
Removes every occurrence of the given str string in this string, and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
这如同
replace(str, "", cs)
.
Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze () after the last change to the string's size.
另请参阅 replace ().
Removes every occurrence of the regular expression re in the string, and returns a reference to the string. For example:
QString r = "Telephone"; r.remove(QRegularExpression("[aeiou].")); // r == "The"
Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze () after the last change to the string's size.
另请参阅 indexOf (), lastIndexOf (),和 replace ().
[since 6.5]
QString
&QString::
removeAt
(
qsizetype
pos
)
Removes the character at index pos 。若 pos is out of bounds (i.e. pos >= size ()), this function does nothing.
该函数在 Qt 6.5 引入。
另请参阅 remove ().
[since 6.5]
QString
&QString::
removeFirst
()
Removes the first character in this string. If the string is empty, this function does nothing.
该函数在 Qt 6.5 引入。
另请参阅 remove ().
[since 6.1]
template <typename Predicate>
QString
&QString::
removeIf
(
Predicate
pred
)
Removes all elements for which the predicate pred returns true from the string. Returns a reference to the string.
该函数在 Qt 6.1 引入。
另请参阅 remove ().
[since 6.5]
QString
&QString::
removeLast
()
Removes the last character in this string. If the string is empty, this function does nothing.
该函数在 Qt 6.5 引入。
另请参阅 remove ().
返回 STL-style reverse iterator pointing just after the last character in the string, in reverse order.
警告: 返回迭代器在分离时是无效的或当 QString 被修改。
另请参阅 end (), crend (),和 rbegin ().
这是重载函数。
Returns a copy of this string repeated the specified number of times .
若 times is less than 1, an empty string is returned.
范例:
QString str("ab"); str.repeated(4); // returns "abababab"
替换 n characters beginning at index position 采用字符串 after and returns a reference to this string.
注意: If the specified position index is within the string, but position + n goes outside the strings range, then n will be adjusted to stop at the end of the string.
范例:
QString x = "Say yes!"; QString y = "no"; x.replace(4, 3, y); // x == "Say no!"
This function overloads replace().
替换 n characters beginning at index position with the character after and returns a reference to this string.
This function overloads replace().
替换 n characters beginning at index position with the first size characters of the QChar array unicode and returns a reference to this string.
This function overloads replace().
Replaces every occurrence of the character before with the character after and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
This function overloads replace().
Replaces each occurrence in this string of the first blen 字符的 before with the first alen 字符的 after and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
This function overloads replace().
Replaces every occurrence in this string of the Latin-1 string viewed by before with the Latin-1 string viewed by after , and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
注意: The text is not rescanned after a replacement.
This function overloads replace().
Replaces every occurrence in this string of the Latin-1 string viewed by before 采用字符串 after , and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
注意: The text is not rescanned after a replacement.
This function overloads replace().
Replaces every occurrence of the string before 采用字符串 after and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
注意: The text is not rescanned after a replacement.
This function overloads replace().
Replaces every occurrence of the string before 采用字符串 after and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
范例:
QString str = "colour behaviour flavour neighbour"; str.replace(QString("ou"), QString("o")); // str == "color behavior flavor neighbor"
注意: The replacement text is not rescanned after it is inserted.
范例:
QString equis = "xxxxxx"; equis.replace("xx", "x"); // equis == "xxx"
This function overloads replace().
Replaces every occurrence of the character ch in the string with after and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
This function overloads replace().
Replaces every occurrence of the character c 采用字符串 after and returns a reference to this string.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
注意: The text is not rescanned after a replacement.
This function overloads replace().
Replaces every occurrence of the regular expression re in the string with after . Returns a reference to the string. For example:
QString s = "Banana"; s.replace(QRegularExpression("a[mn]"), "ox"); // s == "Boxoxa"
For regular expressions containing capturing groups, occurrences of \1 , \2 , ..., in after are replaced with the string captured by the corresponding capturing group.
QString t = "A <i>bon mot</i>."; t.replace(QRegularExpression("<i>([^<]*)</i>"), "\\emph{\\1}"); // t == "A \\emph{bon mot}."
另请参阅 indexOf (), lastIndexOf (), remove (), QRegularExpression ,和 QRegularExpressionMatch .
Ensures the string has space for at least size 字符。
If you know in advance how large the string will be, you can call this function to save repeated reallocation in the course of building it. This can improve performance when building a string incrementally. A long sequence of operations that add to a string may trigger several reallocations, the last of which may leave you with significantly more space than you really need, which is less efficient than doing a single allocation of the right size at the start.
If in doubt about how much space shall be needed, it is usually better to use an upper bound as size , or a high estimate of the most likely size, if a strict upper bound would be much bigger than this. If size is an underestimate, the string will grow as needed once the reserved size is exceeded, which may lead to a larger allocation than your best overestimate would have and will slow the operation that triggers it.
警告: reserve() reserves memory but does not change the size of the string. Accessing data beyond the end of the string is undefined behavior. If you need to access memory beyond the current end of the string, use resize ().
This function is useful for code that needs to build up a long string and wants to avoid repeated reallocation. In this example, we want to add to the string until some condition is
true
, and we're fairly sure that size is large enough to make a call to reserve() worthwhile:
QString result; qsizetype maxSize; bool condition; QChar nextChar; result.reserve(maxSize); while (condition) result.append(nextChar); result.squeeze();
另请参阅 squeeze (), capacity (),和 resize ().
Sets the size of the string to size 字符。
若 size is greater than the current size, the string is extended to make it size characters long with the extra characters added to the end. The new characters are uninitialized.
若 size is less than the current size, characters beyond position size are excluded from the string.
注意: While resize() will grow the capacity if needed, it never shrinks capacity. To shed excess capacity, use squeeze ().
范例:
QString s = "Hello world"; s.resize(5); // s == "Hello" s.resize(8); // s == "Hello???" (where ? stands for any character)
If you want to append a certain number of identical characters to the string, use the resize (qsizetype, QChar) overload.
If you want to expand the string so that it reaches a certain width and fill the new positions with a particular character, use the leftJustified () 函数:
若 size is negative, it is equivalent to passing zero.
QString r = "Hello"; r = r.leftJustified(10, ' '); // r == "Hello "
另请参阅 truncate (), reserve (),和 squeeze ().
这是重载函数。
不像 resize (qsizetype), this overload initializes the new characters to fillChar :
QString t = "Hello"; r.resize(t.size() + 10, 'X'); // t == "HelloXXXXXXXXXX"
Returns a substring that contains the n rightmost characters of the string.
If you know that n cannot be out of bounds, use last () instead in new code, because it is faster.
The entire string is returned if n is greater than or equal to size (), or less than zero.
另请参阅 endsWith (), last (), first (), sliced (), chopped (), chop (),和 truncate ().
Returns a string of size () width 包含 fill character followed by the string. For example:
QString s = "apple"; QString t = s.rightJustified(8, '.'); // t == "...apple"
若
truncate
is
false
和
size
() of the string is more than
width
, then the returned string is a copy of the string.
若 truncate is true and the size () of the string is more than width , then the resulting string is truncated at position width .
QString str = "Pineapple"; str = str.rightJustified(5, '.', true); // str == "Pinea"
另请参阅 leftJustified ().
This function returns a section of the string.
This string is treated as a sequence of fields separated by the character, sep . The returned string consists of the fields from position start to position end inclusive. If end is not specified, all fields from position start to the end of the string are included. Fields are numbered 0, 1, 2, etc., counting from the left, and -1, -2, etc., counting from right to left.
The flags argument can be used to affect some aspects of the function's behavior, e.g. whether to be case sensitive, whether to skip empty fields and how to deal with leading and trailing separators; see SectionFlags .
QString str; QString csv = "forename,middlename,surname,phone"; QString path = "/usr/local/bin/myapp"; // First field is empty QString::SectionFlag flag = QString::SectionSkipEmpty; str = csv.section(',', 2, 2); // str == "surname" str = path.section('/', 3, 4); // str == "bin/myapp" str = path.section('/', 3, 3, flag); // str == "myapp"
若 start or end is negative, we count fields from the right of the string, the right-most field being -1, the one from right-most field being -2, and so on.
str = csv.section(',', -3, -2); // str == "middlename,surname" str = path.section('/', -1); // str == "myapp"
另请参阅 split ().
This function overloads section().
QString str; QString data = "forename**middlename**surname**phone"; str = data.section("**", 2, 2); // str == "surname" str = data.section("**", -3, -2); // str == "middlename**surname"
另请参阅 split ().
This function overloads section().
This string is treated as a sequence of fields separated by the regular expression, re .
QString line = "forename\tmiddlename surname \t \t phone"; QRegularExpression sep("\\s+"); str = line.section(sep, 2, 2); // str == "surname" str = line.section(sep, -3, -2); // str == "middlename surname"
警告: Using this QRegularExpression version is much more expensive than the overloaded string and character versions.
另请参阅 split () 和 simplified ().
Sets the string to the printed value of n 以指定 base , and returns a reference to the string.
The base is 10 by default and must be between 2 and 36.
QString str; str.setNum(1234); // str == "1234"
格式始终使用 QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.
另请参阅 number ().
这是重载函数。
这是重载函数。
这是重载函数。
这是重载函数。
这是重载函数。
这是重载函数。
这是重载函数。
这是重载函数。
Sets the string to the printed value of n , formatted according to the given format and precision , and returns a reference to the string.
格式始终使用 QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.
另请参阅 number ().
这是重载函数。
Sets the string to the printed value of n , formatted according to the given format and precision , and returns a reference to the string.
另请参阅 number (), QLocale::FloatingPointPrecisionOption ,和 Number Formats .
Resets the QString to use the first size Unicode characters in the array unicode . The data in unicode is not copied. The caller must be able to guarantee that unicode will not be deleted or modified as long as the QString (or an unmodified copy of it) exists.
This function can be used instead of fromRawData () to re-use existings QString objects to save memory re-allocations.
另请参阅 fromRawData ().
Resizes the string to size characters and copies unicode into the string.
若
unicode
is
nullptr
, nothing is copied, but the string is still resized to
size
.
另请参阅 unicode () 和 setUtf16 ().
Resizes the string to size characters and copies unicode into the string.
若
unicode
is
nullptr
, nothing is copied, but the string is still resized to
size
.
Note that unlike fromUtf16 (), this function does not consider BOMs and possibly differing byte ordering.
另请参阅 utf16 () 和 setUnicode ().
提供此函数是为兼容 STL。它相当于 squeeze ().
另请参阅 squeeze ().
Returns a string that has whitespace removed from the start and the end, and that has each sequence of internal whitespace replaced with a single space.
Whitespace means any character for which
QChar::isSpace
() 返回
true
. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
范例:
QString str = " lots\t of\nwhitespace\r\n "; str = str.simplified(); // str == "lots of whitespace";
另请参阅 trimmed ().
Returns the number of characters in this string.
The last character in the string is at position size() - 1.
范例:
QString str = "World"; qsizetype n = str.size(); // n == 5 str.data()[0]; // returns 'W' str.data()[4]; // returns 'd'
[since 6.0]
QString
QString::
sliced
(
qsizetype
pos
,
qsizetype
n
) const
Returns a string that contains n characters of this string, starting at position pos .
注意: The behavior is undefined when pos < 0, n < 0, or pos + n > size ().
QString x = "Nine pineapples"; QString y = x.sliced(5, 4); // y == "pine" QString z = x.sliced(5); // z == "pineapples"
该函数在 Qt 6.0 引入。
另请参阅 first (), last (), chopped (), chop (),和 truncate ().
[since 6.0]
QString
QString::
sliced
(
qsizetype
pos
) const
这是重载函数。
Returns a string that contains the portion of this string starting at position pos and extending to its end.
注意: The behavior is undefined when pos < 0 or pos > size ().
该函数在 Qt 6.0 引入。
另请参阅 first (), last (), sliced (), chopped (), chop (),和 truncate ().
Splits the string into substrings wherever sep occurs, and returns the list of those strings. If sep does not match anywhere in the string, split() returns a single-element list containing this string.
cs specifies whether sep should be matched case sensitively or case insensitively.
若 behavior is Qt::SkipEmptyParts , empty entries don't appear in the result. By default, empty entries are kept.
范例:
QString str = QStringLiteral("a,,b,c"); QStringList list1 = str.split(u','); // list1: [ "a", "", "b", "c" ] QStringList list2 = str.split(u',', Qt::SkipEmptyParts); // list2: [ "a", "b", "c" ]
若 sep is empty, split() returns an empty string, followed by each of the string's characters, followed by another empty string:
QString str = "abc"; auto parts = str.split(QString()); // parts: {"", "a", "b", "c", ""}
To understand this behavior, recall that the empty string matches everywhere, so the above is qualitatively the same as:
QString str = "/a/b/c/"; auto parts = str.split(u'/'); // parts: {"", "a", "b", "c", ""}
另请参阅 QStringList::join () 和 section ().
这是重载函数。
这是重载函数。
Splits the string into substrings wherever the regular expression re matches, and returns the list of those strings. If re does not match anywhere in the string, split() returns a single-element list containing this string.
Here is an example where we extract the words in a sentence using one or more whitespace characters as the separator:
QString str; QStringList list; str = "Some text\n\twith strange whitespace."; list = str.split(QRegularExpression("\\s+")); // list: [ "Some", "text", "with", "strange", "whitespace." ]
Here is a similar example, but this time we use any sequence of non-word characters as the separator:
str = "This time, a normal English sentence."; list = str.split(QRegularExpression("\\W+"), Qt::SkipEmptyParts); // list: [ "This", "time", "a", "normal", "English", "sentence" ]
Here is a third example where we use a zero-length assertion, \b (word boundary), to split the string into an alternating sequence of non-word and word tokens:
str = "Now: this sentence fragment."; list = str.split(QRegularExpression("\\b")); // list: [ "", "Now", ": ", "this", " ", "sentence", " ", "fragment", "." ]
另请参阅 QStringList::join () 和 section ().
Releases any memory not required to store the character data.
The sole purpose of this function is to provide a means of fine tuning QString 's memory usage. In general, you will rarely ever need to call this function.
另请参阅 reserve () 和 capacity ().
返回
true
if the string starts with
s
;否则返回
false
.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
QString str = "Bananas"; str.startsWith("Ban"); // returns true str.startsWith("Car"); // returns false
另请参阅 endsWith ().
这是重载函数。
返回
true
if the string starts with the string view
str
;否则返回
false
.
若 cs is Qt::CaseSensitive (the default), the search is case-sensitive; otherwise the search is case-insensitive.
另请参阅 endsWith ().
This function overloads startsWith().
This function overloads startsWith().
返回
true
if the string starts with
c
;否则返回
false
.
Swaps string other with this string. This operation is very fast and never fails.
Creates a CFString from a QString .
The caller owns the CFString and is responsible for releasing it.
注意: this function is only available on macOS and iOS.
Returns the case folded equivalent of the string. For most Unicode characters this is the same as toLower ().
Returns the string converted to a
double
值。
Returns an infinity if the conversion overflows or 0.0 if the conversion fails for other reasons (e.g. underflow).
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
QString str = "1234.56"; double val = str.toDouble(); // val == 1234.56
警告: The QString content may only contain valid numerical characters which includes the plus/minus sign, the character e used in scientific notation, and the decimal point. Including the unit or additional characters leads to a conversion error.
bool ok; double d; d = QString( "1234.56e-02" ).toDouble(&ok); // ok == true, d == 12.3456 d = QString( "1234.56e-02 Volt" ).toDouble(&ok); // ok == false, d == 0
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toDouble ()
d = QString( "1234,56" ).toDouble(&ok); // ok == false d = QString( "1234.56" ).toDouble(&ok); // ok == true, d == 1234.56
For historical reasons, this function does not handle thousands group separators. If you need to convert such numbers, use QLocale::toDouble ().
d = QString( "1,234,567.89" ).toDouble(&ok); // ok == false d = QString( "1234567.89" ).toDouble(&ok); // ok == true
此函数忽略前导和结尾空格。
另请参阅 number (), QLocale::setDefault (), QLocale::toDouble (),和 trimmed ().
Returns the string converted to a
float
值。
Returns an infinity if the conversion overflows or 0.0 if the conversion fails for other reasons (e.g. underflow).
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
警告: The QString content may only contain valid numerical characters which includes the plus/minus sign, the character e used in scientific notation, and the decimal point. Including the unit or additional characters leads to a conversion error.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toFloat ()
For historical reasons, this function does not handle thousands group separators. If you need to convert such numbers, use QLocale::toFloat ().
范例:
QString str1 = "1234.56"; str1.toFloat(); // returns 1234.56 bool ok; QString str2 = "R2D2"; str2.toFloat(&ok); // returns 0.0, sets ok to false QString str3 = "1234.56 Volt"; str3.toFloat(&ok); // returns 0.0, sets ok to false
此函数忽略前导和结尾空格。
另请参阅 number (), toDouble (), toInt (), QLocale::toFloat (),和 trimmed ().
Converts a plain text string to an HTML string with HTML metacharacters
<
,
>
,
&
,和
"
replaced by HTML entities.
范例:
QString plain = "#include <QtCore>" QString html = plain.toHtmlEscaped(); // html == "#include <QtCore>"
Returns the string converted to an
int
using base
base
, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
若 base is 0, the C language convention is used: if the string begins with "0x", base 16 is used; otherwise, if the string begins with "0b", base 2 is used; otherwise, if the string begins with "0", base 8 is used; otherwise, base 10 is used.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toInt ()
范例:
QString str = "FF"; bool ok; int hex = str.toInt(&ok, 16); // hex == 255, ok == true int dec = str.toInt(&ok, 10); // dec == 0, ok == false
此函数忽略前导和结尾空格。
注意: Support for the "0b" prefix was added in Qt 6.4.
另请参阅 number (), toUInt (), toDouble (),和 QLocale::toInt ().
Returns a Latin-1 representation of the string as a QByteArray .
The returned byte array is undefined if the string contains non-Latin1 characters. Those characters may be suppressed or replaced with a question mark.
另请参阅 fromLatin1 (), toUtf8 (), toLocal8Bit (),和 QStringEncoder .
Returns the local 8-bit representation of the string as a QByteArray .
On Unix systems this is equivalent to toUtf8 (), on Windows the systems current code page is being used.
If this string contains any characters that cannot be encoded in the local 8-bit encoding, the returned byte array is undefined. Those characters may be suppressed or replaced by another.
另请参阅 fromLocal8Bit (), toLatin1 (), toUtf8 (),和 QStringEncoder .
Returns the string converted to a
long
using base
base
, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
若 base is 0, the C language convention is used: if the string begins with "0x", base 16 is used; otherwise, if the string begins with "0b", base 2 is used; otherwise, if the string begins with "0", base 8 is used; otherwise, base 10 is used.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toLongLong ()
范例:
QString str = "FF"; bool ok; long hex = str.toLong(&ok, 16); // hex == 255, ok == true long dec = str.toLong(&ok, 10); // dec == 0, ok == false
此函数忽略前导和结尾空格。
注意: Support for the "0b" prefix was added in Qt 6.4.
另请参阅 number (), toULong (), toInt (),和 QLocale::toInt ().
Returns the string converted to a
long long
using base
base
, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
若 base is 0, the C language convention is used: if the string begins with "0x", base 16 is used; otherwise, if the string begins with "0b", base 2 is used; otherwise, if the string begins with "0", base 8 is used; otherwise, base 10 is used.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toLongLong ()
范例:
QString str = "FF"; bool ok; qint64 hex = str.toLongLong(&ok, 16); // hex == 255, ok == true qint64 dec = str.toLongLong(&ok, 10); // dec == 0, ok == false
此函数忽略前导和结尾空格。
注意: Support for the "0b" prefix was added in Qt 6.4.
另请参阅 number (), toULongLong (), toInt (),和 QLocale::toLongLong ().
Returns a lowercase copy of the string.
QString str = "The Qt PROJECT"; str = str.toLower(); // str == "the qt project"
The case conversion will always happen in the 'C' locale. For locale-dependent case folding use QLocale::toLower ()
另请参阅 toUpper () 和 QLocale::toLower ().
Creates a NSString from a QString .
The NSString is autoreleased.
注意: this function is only available on macOS and iOS.
Returns the string converted to a
short
using base
base
, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
若 base is 0, the C language convention is used: if the string begins with "0x", base 16 is used; otherwise, if the string begins with "0b", base 2 is used; otherwise, if the string begins with "0", base 8 is used; otherwise, base 10 is used.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toShort ()
范例:
QString str = "FF"; bool ok; short hex = str.toShort(&ok, 16); // hex == 255, ok == true short dec = str.toShort(&ok, 10); // dec == 0, ok == false
此函数忽略前导和结尾空格。
注意: Support for the "0b" prefix was added in Qt 6.4.
另请参阅 number (), toUShort (), toInt (),和 QLocale::toShort ().
Returns a std::string object with the data contained in this QString . The Unicode data is converted into 8-bit characters using the toUtf8 () 函数。
This method is mostly useful to pass a QString to a function that accepts a std::string object.
另请参阅 toLatin1 (), toUtf8 (), toLocal8Bit (),和 QByteArray::toStdString ().
Returns a std::u16string object with the data contained in this QString . The Unicode data is the same as returned by the utf16 () 方法。
另请参阅 utf16 (), toStdWString (),和 toStdU32String ().
Returns a std::u32string object with the data contained in this QString . The Unicode data is the same as returned by the toUcs4 () 方法。
另请参阅 toUcs4 (), toStdWString (),和 toStdU16String ().
Returns a std::wstring object with the data contained in this QString . The std::wstring is encoded in utf16 on platforms where wchar_t is 2 bytes wide (e.g. windows) and in ucs4 on platforms where wchar_t is 4 bytes wide (most Unix systems).
This method is mostly useful to pass a QString to a function that accepts a std::wstring object.
另请参阅 utf16 (), toLatin1 (), toUtf8 (), toLocal8Bit (), toStdU16String (),和 toStdU32String ().
Returns the string converted to an
无符号 int
using base
base
, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
若 base is 0, the C language convention is used: if the string begins with "0x", base 16 is used; otherwise, if the string begins with "0b", base 2 is used; otherwise, if the string begins with "0", base 8 is used; otherwise, base 10 is used.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toUInt ()
范例:
QString str = "FF"; bool ok; uint hex = str.toUInt(&ok, 16); // hex == 255, ok == true uint dec = str.toUInt(&ok, 10); // dec == 0, ok == false
此函数忽略前导和结尾空格。
注意: Support for the "0b" prefix was added in Qt 6.4.
另请参阅 number (), toInt (),和 QLocale::toUInt ().
Returns the string converted to an
unsigned long
using base
base
, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
若 base is 0, the C language convention is used: if the string begins with "0x", base 16 is used; otherwise, if the string begins with "0b", base 2 is used; otherwise, if the string begins with "0", base 8 is used; otherwise, base 10 is used.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toULongLong ()
范例:
QString str = "FF"; bool ok; ulong hex = str.toULong(&ok, 16); // hex == 255, ok == true ulong dec = str.toULong(&ok, 10); // dec == 0, ok == false
此函数忽略前导和结尾空格。
注意: Support for the "0b" prefix was added in Qt 6.4.
另请参阅 number () 和 QLocale::toUInt ().
Returns the string converted to an
unsigned long long
using base
base
, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
若 base is 0, the C language convention is used: if the string begins with "0x", base 16 is used; otherwise, if the string begins with "0b", base 2 is used; otherwise, if the string begins with "0", base 8 is used; otherwise, base 10 is used.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toULongLong ()
范例:
QString str = "FF"; bool ok; quint64 hex = str.toULongLong(&ok, 16); // hex == 255, ok == true quint64 dec = str.toULongLong(&ok, 10); // dec == 0, ok == false
此函数忽略前导和结尾空格。
注意: Support for the "0b" prefix was added in Qt 6.4.
另请参阅 number (), toLongLong (),和 QLocale::toULongLong ().
Returns the string converted to an
unsigned short
using base
base
, which is 10 by default and must be between 2 and 36, or 0. Returns 0 if the conversion fails.
若
ok
不是
nullptr
, failure is reported by setting *
ok
to
false
, and success by setting *
ok
to
true
.
若 base is 0, the C language convention is used: if the string begins with "0x", base 16 is used; otherwise, if the string begins with "0b", base 2 is used; otherwise, if the string begins with "0", base 8 is used; otherwise, base 10 is used.
The string conversion will always happen in the 'C' locale. For locale-dependent conversion use QLocale::toUShort ()
范例:
QString str = "FF"; bool ok; ushort hex = str.toUShort(&ok, 16); // hex == 255, ok == true ushort dec = str.toUShort(&ok, 10); // dec == 0, ok == false
此函数忽略前导和结尾空格。
注意: Support for the "0b" prefix was added in Qt 6.4.
另请参阅 number (), toShort (),和 QLocale::toUShort ().
Returns a UCS-4/UTF-32 representation of the string as a QList <uint>.
UCS-4 is a Unicode codec and therefore it is lossless. All characters from this string will be encoded in UCS-4. Any invalid sequence of code units in this string is replaced by the Unicode's replacement character (
QChar::ReplacementCharacter
, which corresponds to
U+FFFD
).
The returned list is not \0'-terminated.
另请参阅 fromUtf8 (), toUtf8 (), toLatin1 (), toLocal8Bit (), QStringEncoder , fromUcs4 (),和 toWCharArray ().
Returns an uppercase copy of the string.
QString str = "TeXt"; str = str.toUpper(); // str == "TEXT"
The case conversion will always happen in the 'C' locale. For locale-dependent case folding use QLocale::toUpper ()
另请参阅 toLower () 和 QLocale::toLower ().
Returns a UTF-8 representation of the string as a QByteArray .
UTF-8 is a Unicode codec and can represent all characters in a Unicode string like QString .
另请参阅 fromUtf8 (), toLatin1 (), toLocal8Bit (),和 QStringEncoder .
Fills the array with the data contained in this QString object. The array is encoded in UTF-16 on platforms where wchar_t is 2 bytes wide (e.g. windows) and in UCS-4 on platforms where wchar_t is 4 bytes wide (most Unix systems).
array has to be allocated by the caller and contain enough space to hold the complete string (allocating the array with the same length as the string is always sufficient).
This function returns the actual length of the string in array .
注意: This function does not append a null character to the array.
另请参阅 utf16 (), toUcs4 (), toLatin1 (), toUtf8 (), toLocal8Bit (), toStdWString (),和 QStringView::toWCharArray ().
Returns a string that has whitespace removed from the start and the end.
Whitespace means any character for which
QChar::isSpace
() 返回
true
. This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.
范例:
QString str = " lots\t of\nwhitespace\r\n "; str = str.trimmed(); // str == "lots\t of\nwhitespace"
不像 simplified (), trimmed() leaves internal whitespace alone.
另请参阅 simplified ().
Truncates the string at the given position 索引。
If the specified position index is beyond the end of the string, nothing happens.
范例:
QString str = "Vladivostok"; str.truncate(4); // str == "Vlad"
若 position is negative, it is equivalent to passing zero.
另请参阅 chop (), resize (), first (),和 QStringView::truncate ().
Returns a Unicode representation of the string. The result remains valid until the string is modified.
注意: The returned string may not be '\0'-terminated. Use size () to determine the length of the array.
另请参阅 setUnicode (), utf16 (),和 fromRawData ().
返回 QString as a '\0'-terminated array of unsigned shorts. The result remains valid until the string is modified.
The returned string is in host byte order.
另请参阅 setUtf16 () 和 unicode ().
[static]
QString
QString::
vasprintf
(const
char
*
cformat
,
va_list
ap
)
Equivalent method to asprintf (), but takes a va_list ap instead a list of variable arguments. See the asprintf () documentation for an explanation of cformat .
This method does not call the va_end macro, the caller is responsible to call va_end on ap .
另请参阅 asprintf ().
This function overloads operator!=().
The other const char pointer is converted to a QString 使用 fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator!=().
The other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
追加字符串 other onto the end of this string and returns a reference to this string.
范例:
QString x = "free"; QString y = "dom"; x += y; // x == "freedom"
This operation is typically very fast ( 常量时间 ),因为 QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.
This function overloads operator+=().
追加字符 ch to the string.
[since 6.0]
QString
&QString::
operator+=
(
QStringView
str
)
This function overloads operator+=().
Appends the string view str 到此字符串。
该函数在 Qt 6.0 引入。
This function overloads operator+=().
Appends the Latin-1 string viewed by str 到此字符串。
[since 6.5]
QString
&QString::
operator+=
(
QUtf8StringView
str
)
This function overloads operator+=().
Appends the UTF-8 string view str 到此字符串。
该函数在 Qt 6.5 引入。
This function overloads operator+=().
追加字符串 str to this string. The const char pointer is converted to Unicode using the fromUtf8 () 函数。
可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator+=().
追加字节数组 ba to this string. The byte array is converted to Unicode using the fromUtf8 () function. If any NUL characters ('\0') are embedded in the ba byte array, they will be included in the transformation.
可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
返回
true
if this string is lexically less than string
other
. Otherwise returns
false
.
This function overloads operator<().
The other const char pointer is converted to a QString 使用 fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator<().
The other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.
You can disable this operator QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator<=().
The other const char pointer is converted to a QString 使用 fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator<=().
The other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
赋值 other to this string and returns a reference to this string.
此函数重载 operator=()。
Sets the string to contain the single character ch .
此函数重载 operator=()。
Assigns the Latin-1 string viewed by str 到此字符串。
移动赋值 other 到此 QString 实例。
此函数重载 operator=()。
赋值 str to this string. The const char pointer is converted to Unicode using the fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII or QT_RESTRICTED_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
此函数重载 operator=()。
赋值 ba to this string. The byte array is converted to Unicode using the fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator==().
The other const char pointer is converted to a QString 使用 fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator==().
The other byte array is converted to a QString 使用 fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
返回
true
if this string is lexically equal to the parameter string
other
. Otherwise returns
false
.
This function overloads operator>().
The other const char pointer is converted to a QString 使用 fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator>().
The other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator>=().
The other const char pointer is converted to a QString 使用 fromUtf8 () 函数。
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
This function overloads operator>=().
The other byte array is converted to a QString 使用 fromUtf8 () function. If any NUL characters ('\0') are embedded in the byte array, they will be included in the transformation.
可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.
Returns the character at the specified position in the string as a modifiable reference.
范例:
QString str; if (str[0] == QChar('?')) str[0] = QChar('_');
另请参阅 at ().
This function overloads operator[]().
Returns a string which is the result of concatenating s1 and s2 .
[since 6.1]
template <typename T>
qsizetype
erase
(
QString
&
s
, const
T
&
t
)
Removes all elements that compare equal to t 从字符串 s . Returns the number of elements removed, if any.
该函数在 Qt 6.1 引入。
另请参阅 erase_if .
[since 6.1]
template <typename Predicate>
qsizetype
erase_if
(
QString
&
s
,
Predicate
pred
)
Removes all elements for which the predicate pred returns true from the string s . Returns the number of elements removed, if any.
该函数在 Qt 6.1 引入。
另请参阅 erase .
返回
true
若字符串
s1
不等于字符串
s2
;否则返回
false
.
另请参阅 Comparing Strings .
返回
true
若字符串
s1
不等于字符串
s2
. Otherwise returns
false
.
This function overloads operator!=().
返回
true
if
s1
不等于
s2
;否则返回
false
.
For
s1
!= 0, this is equivalent to
compare(
s1
,
s2
) != 0
. Note that no string is equal to
s1
being 0.
[since 6.4]
QString
operator""_s
(const
char16_t
*
str
,
size_t
size
)
文字运算符创建的 QString out of the first size characters in the char16_t string literal str .
The QString is created at compile time, and the generated string data is stored in the read-only segment of the compiled object file. Duplicate literals may share the same read-only memory. This functionality is interchangeable with QStringLiteral , but saves typing when many string literals are present in the code.
以下代码创建 QString :
using namespace Qt::Literals::StringLiterals; auto str = u"hello"_s;
该函数在 Qt 6.4 引入。
另请参阅 Qt::Literals::StringLiterals .
Returns a string which is the result of concatenating s1 and s2 ( s2 is converted to Unicode using the QString::fromUtf8 () 函数)。
另请参阅 QString::fromUtf8 ().
Returns a string which is the result of concatenating s1 and s2 ( s1 is converted to Unicode using the QString::fromUtf8 () 函数)。
另请参阅 QString::fromUtf8 ().
This function overloads operator<().
返回
true
若字符串
s1
词法上小于字符串
s2
;否则返回
false
.
另请参阅 Comparing Strings .
This function overloads operator<().
返回
true
if
s1
is lexically less than
s2
;否则返回
false
.
This function overloads operator<().
返回
true
if
s1
is lexically less than
s2
;否则返回
false
.
返回
true
if
s1
is lexically less than
s2
;否则返回
false
。对于
s1
!= 0, this is equivalent to
compare(s1, s2) < 0
.
另请参阅 Comparing Strings .
写入给定 string 到指定 stream .
另请参阅 序列化 Qt 数据类型 .
返回
true
若字符串
s1
词法上小于等于字符串
s2
;否则返回
false
.
另请参阅 Comparing Strings .
This function overloads operator<=().
返回
true
if
s1
is lexically less than or equal to
s2
;否则返回
false
.
This function overloads operator<=().
返回
true
if
s1
is lexically less than or equal to
s2
;否则返回
false
.
返回
true
if
s1
is lexically less than or equal to
s2
;否则返回
false
。对于
s1
!= 0, this is equivalent to
compare(s1, s2) <= 0
.
另请参阅 Comparing Strings .
This function overloads operator==().
返回
true
若字符串
s1
等于字符串
s2
;否则返回
false
.
注意: This function treats null strings the same as empty strings, for more details see Null 和空字符串之间的区别 .
另请参阅 Comparing Strings .
This function overloads operator==().
返回
true
if
s1
等于
s2
;否则返回
false
.
This function overloads operator==().
返回
true
if
s1
等于
s2
;否则返回
false
.
This function overloads operator==().
返回
true
if
s1
等于
s2
;否则返回
false
. Note that no string is equal to
s1
being 0.
相当于
s1 != 0 && compare(s1, s2) == 0
.
返回
true
若字符串
s1
词法上大于字符串
s2
;否则返回
false
.
另请参阅 Comparing Strings .
This function overloads operator>().
返回
true
if
s1
is lexically greater than
s2
;否则返回
false
.
This function overloads operator>().
返回
true
if
s1
is lexically greater than
s2
;否则返回
false
.
返回
true
if
s1
is lexically greater than
s2
;否则返回
false
. Equivalent to
compare(s1, s2) > 0
.
另请参阅 Comparing Strings .
返回
true
若字符串
s1
词法上大于等于字符串
s2
;否则返回
false
.
另请参阅 Comparing Strings .
This function overloads operator>=().
返回
true
if
s1
is lexically greater than or equal to
s2
;否则返回
false
.
This function overloads operator>=().
返回
true
if
s1
is lexically greater than or equal to
s2
;否则返回
false
.
返回
true
if
s1
is lexically greater than or equal to
s2
;否则返回
false
。对于
s1
!= 0, this is equivalent to
compare(s1, s2) >= 0
.
另请参阅 Comparing Strings .
Reads a string from the specified stream 进给定 string .
另请参阅 序列化 Qt 数据类型 .
宏生成数据为 QString 从字符串文字 str 在编译时。创建 QString from it is free in this case, and the generated string data is stored in the read-only segment of the compiled object file.
If you have code that looks like this:
// hasAttribute takes a QString argument if (node.hasAttribute("http-contents-length")) //...
then a temporary
QString
will be created to be passed as the
hasAttribute
function parameter. This can be quite expensive, as it involves a memory allocation and the copy/conversion of the data into
QString
's internal encoding.
This cost can be avoided by using QStringLiteral instead:
if (node.hasAttribute(QStringLiteral(u"http-contents-length"))) //...
In this case, QString 's internal data will be generated at compile time; no conversion or allocation will occur at runtime.
Using QStringLiteral instead of a double quoted plain C++ string literal can significantly speed up creation of QString 实例从编译时的已知数据。
注意: QLatin1StringView can still be more efficient than QStringLiteral when the string is passed to a function that has an overload taking QLatin1StringView and this overload avoids conversion to QString . For instance, QString::operator==() can compare to a QLatin1StringView 直接:
if (attribute.name() == "http-contents-length"_L1) //...
注意:
Some compilers have bugs encoding strings containing characters outside the US-ASCII character set. Make sure you prefix your string with
u
in those cases. It is optional otherwise.
另请参阅 QByteArrayLiteral .
Disables automatic conversions from 8-bit strings (
char *
) to Unicode QStrings, as well as from 8-bit
char
types (
char
and
unsigned char
) 到
QChar
.
另请参阅 QT_NO_CAST_TO_ASCII , QT_RESTRICTED_CAST_FROM_ASCII ,和 QT_NO_CAST_FROM_BYTEARRAY .
Disables automatic conversion from
QString
to 8-bit strings (
char *
).
另请参阅 QT_NO_CAST_FROM_ASCII , QT_RESTRICTED_CAST_FROM_ASCII ,和 QT_NO_CAST_FROM_BYTEARRAY .
Disables most automatic conversions from source literals and 8-bit data to unicode QStrings, but allows the use of the
QChar(char)
and
QString(const char (&ch)[N]
constructors, and the
QString::operator=(const char (&ch)[N])
assignment operator. This gives most of the type-safety benefits of
QT_NO_CAST_FROM_ASCII
but does not require user code to wrap character and string literals with
QLatin1Char
,
QLatin1StringView
or similar.
Using this macro together with source strings outside the 7-bit range, non-literals, or literals with embedded NUL characters is undefined.
另请参阅 QT_NO_CAST_FROM_ASCII and QT_NO_CAST_TO_ASCII .
返回
str
作为
const char *
。这相当于
str
.
toLocal8Bit
().
constData
().
The char pointer will be invalid after the statement in which qPrintable() is used. This is because the array returned by QString::toLocal8Bit () will fall out of scope.
注意: qDebug (), qInfo (), qWarning (), qCritical (), qFatal () expect %s arguments to be UTF-8 encoded, while qPrintable() converts to local 8-bit encoding. Therefore qUtf8Printable () should be used for logging strings instead of qPrintable().
另请参阅 qUtf8Printable ().
返回
str
作为
const ushort *
, but cast to a
const wchar_t *
to avoid warnings. This is equivalent to
str
.
utf16
() plus some casting.
The only useful thing you can do with the return value of this macro is to pass it to
QString::asprintf
() for use in a
%ls
conversion. In particular, the return value is
not
a valid
const wchar_t*
!
In general, the pointer will be invalid after the statement in which qUtf16Printable() is used. This is because the pointer may have been obtained from a temporary expression, which will fall out of scope.
范例:
qWarning("%ls: %ls", qUtf16Printable(key), qUtf16Printable(value));
另请参阅 qPrintable (), qDebug (), qInfo (), qWarning (), qCritical (),和 qFatal ().
返回
str
作为
const char *
。这相当于
str
.
toUtf8
().
constData
().
The char pointer will be invalid after the statement in which qUtf8Printable() is used. This is because the array returned by QString::toUtf8 () will fall out of scope.
范例:
qWarning("%s: %s", qUtf8Printable(key), qUtf8Printable(value));
另请参阅 qPrintable (), qDebug (), qInfo (), qWarning (), qCritical (),和 qFatal ().