QString 類

QString 類提供 Unicode 字符串。 更多...

• 所有成員列錶，包括繼承成員
• Deprecated members
• QString is part of 隱式共享類 and 用於字符串數據的類 .

注意： 此類的所有函數 可重入 .

公共類型

公共函數

靜態公共成員

相關非成員

宏

詳細描述

QString 存儲字符串的 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 )。

Unicode 是支持當今使用的大多數書寫係統的國際標準。它是 US-ASCII (ANSI X3.4-1986) 和 Latin-1 (ISO 8859-1) 的超集，且所有 US-ASCII/Latin-1 字符可用於相同代碼位置。

在幕後，QString 使用 隱式共享 (寫時拷貝) 以縮減內存用量並避免不必要的數據拷貝。這還有助於縮減存儲 16 位字符而不是 8 位字符的固有開銷。

除 QString 外，Qt 還提供 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 是閤適的，當需要存儲原生二進製數據時，和當內存守恒臨界時 (像在嵌入式係統)。

初始化字符串

One way to initialize a QString is simply to pass a const char * 到其構造函數。例如，以下代碼創建包含數據 Hello 大小為 5 的 QString：

QString str = "Hello";
					

QString 轉換 const char * 數據成 Unicode 使用 fromUtf8 () 函數。

QString 的所有函數都接受 const char * 參數， 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 .

還可以將字符串數據提供成數組化的 QChar ：

static const QChar data[4] = { 0x0055, 0x006e, 0x10e3, 0x03a3 };
QString str(data, 4);
					

QString 製作深拷貝對 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.)

另一種方式是設置字符串大小使用 resize () 並逐字符初始化數據。QString 使用基於 0 的索引，就像 C++ 數組。要訪問位於特定索引位置的字符，可以使用 operator[] (). On non- const strings, operator[] () 返迴可以用於賦值左側的字符引用。例如：

QString str;
str.resize(4);
str[0] = QChar('U');
str[1] = QChar('n');
str[2] = QChar(0x10e3);
str[3] = QChar(0x03a3);
					

對於隻讀訪問，替代句法是使用 at () 函數：

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 () 函數可以更快相比 operator[] (), because it never causes a 深拷貝 的齣現。另外，使用 first (), last ()，或 sliced () 函數能一次提取幾個字符。

QString 可以嵌入 \0 字符 ( QChar::Null )。 size () 函數始終返迴整個字符串的大小，包括嵌入 \0 字符。

後於調用 resize () 函數，新近分配字符擁有未定義值。要把字符串中的所有字符設為特定值，使用 fill () 函數。

QString 提供瞭很多設計用於簡化字符串用法的重載。例如，若想要比較 QString 與字符串文字，可以像這樣編寫代碼且它會如期望般工作：

QString str;
if (str == "auto" || str == "extern"
        || str == "static" || str == "register") {
    // ...
}
					

還可以把字符串文字傳遞給接受 QString 作為自變量的函數，援引 QString(const char *) 構造函數。同樣，可以傳遞 QString 的函數接受 const char * 自變量使用 qPrintable () macro which returns the given QString as a const char * 。這相當於調用 <QString>. toLocal8Bit (). constData ().

操縱字符串數據

QString 提供修改字符數據的基本功能： 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 ( 綫性時間 ) for large strings, because they require moving many characters in the string by at least one position in memory.

若正逐步構建 QString 且提前大概知道 QString 將包含多少個字符，可以調用 reserve ()，要求 QString 預分配一定數量的內存。也可以調用 capacity () to find out how much memory the QString actually has allocated.

QString provides STL 樣式迭代器 ( 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 隱式共享 , 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 ().

若想要查找 QString 中的特定字符 (或子字符串) 的所有齣現，使用 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 提供瞭很多按數字轉換成字符串，和把字符串轉換成數字的函數。見 arg () 函數， setNum () 函數， number () 靜態函數，和 toInt (), toDouble ()，及類似函數。

To get an upper- or lowercase version of a string use toUpper () 或 toLower ().

字符串列錶的處理是通過 QStringList 類。可以把字符串分割成字符串列錶使用 split () 函數，和把字符串列錶聯接成單字符串采用可選分隔符使用 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 () 函數。

查詢字符串數據

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().

要獲得實際字符數據指針，調用 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.

Comparing Strings

可以比較 QString 使用重載運算符譬如 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() ,

Converting Between Encoded Strings Data and QString

QString provides the following three functions that return a const char * 版本的字符串如 QByteArray : toUtf8 (), toLatin1 ()，和 toLocal8Bit ().

• toLatin1 () 返迴 Latin-1 (ISO 8859-1) 編碼 8 位字符串。
• toUtf8 () 返迴 UTF-8 編碼 8 位字符串。UTF-8 是 US-ASCII (ANSI X3.4-1986) 超集，支持透過多字節序列的整個 Unicode 字符集。
• toLocal8Bit () returns an 8-bit string using the system's local encoding. This is the same as toUtf8 () on Unix systems.

要轉換自這些編碼之一，QString 提供 fromLatin1 (), fromUtf8 ()，和 fromLocal8Bit ()。其它編碼的支持是透過 QStringEncoder and QStringDecoder 類。

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:

• QT_NO_CAST_FROM_ASCII disables automatic conversions from C string literals and pointers to Unicode.
• QT_RESTRICTED_CAST_FROM_ASCII allows automatic conversions from C characters and character arrays, but disables automatic conversions from character pointers to Unicode.
• QT_NO_CAST_TO_ASCII disables automatic conversion from QString to C strings.

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;
					

同樣，必須調用 toLatin1 (), toUtf8 ()，或 toLocal8Bit () explicitly to convert the QString to an 8-bit string.

QString Widget::boolToString(bool b)
{


QString


 result;

if

 (b)
result

=


"True"

;

else

result

=


"False"

;

return

 result;
}
								

null 和空字符串之間的區彆

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
						

所有函數除瞭 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 ().

Number Formats

當 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.

當 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.

Floating-point Formats

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.

更高效的字符串構造

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.

使用 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 () 需要額外測試)。

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 '%' 運算符而不是 '+' 當串聯字符串時：

    #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.

最大尺寸和內存不足情況

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.

另請參閱 fromRawData (), QChar , QStringView , QLatin1StringView ，和 QByteArray .

成員類型文檔編製

QString:: ConstIterator

Qt 樣式同義詞 QString::const_iterator .

QString:: Iterator

Qt 樣式同義詞 QString::iterator .

enum QString:: NormalizationForm

此枚舉描述 Unicode 文本的各種規範化形式。

另請參閱 normalized () 和 Unicode 標準附錄 #15 .

enum QString:: SectionFlag
flags QString:: SectionFlags

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.

SectionFlags 類型是 typedef 對於 QFlags <SectionFlag>. It stores an OR combination of SectionFlag values.

另請參閱 section ().

QString:: const_iterator

另請參閱 QString::iterator .

QString:: const_pointer

The QString::const_pointer typedef provides an STL-style const pointer to a QString 元素 ( QChar ).

QString:: const_reference

QString:: const_reverse_iterator

另請參閱 QString::reverse_iterator and QString::const_iterator .

QString:: difference_type

QString:: iterator

另請參閱 QString::const_iterator .

QString:: pointer

The QString::pointer typedef provides an STL-style pointer to a QString 元素 ( QChar ).

QString:: reference

QString:: reverse_iterator

另請參閱 QString::const_reverse_iterator and QString::iterator .

QString:: size_type

QString:: value_type

成員函數文檔編製

template <typename Args> QString QString:: arg ( Args &&... args ) const

Replaces occurrences of %N in this string with the corresponding argument from args . The arguments are not positional: the first of the args 替換 %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 .

另請參閱 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.

相當於

return QStringTokenizer{std::forward<Needle>(sep), flags...};
						

except it works without C++17 Class Template Argument Deduction (CTAD) enabled in the compiler.

見 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.

該函數在 Qt 6.0 引入。

另請參閱 QStringTokenizer and qTokenize ().

[constexpr] QString:: QString ()

Constructs a null string. Null strings are also considered empty.

另請參閱 isEmpty (), isNull ()，和 null 和空字符串之間的區彆 .

[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 為 0，構造 null 字符串。

若 size 為負， 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.

另請參閱 fromRawData ().

QString:: QString ( QChar ch )

Constructs a string of size 1 containing the character ch .

QString:: QString ( qsizetype size , QChar ch )

Constructs a string of the given size with every character set to ch .

另請參閱 fill ().

QString:: QString ( QLatin1StringView str )

Constructs a copy of the Latin-1 string viewed by str .

另請參閱 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 () 函數。

This function was introduced in Qt 6.1.

另請參閱 fromLatin1 (), fromLocal8Bit ()，和 fromUtf8 ().

QString:: QString (const char * str )

Constructs a string initialized with the 8-bit string str . The given const char pointer is converted to Unicode using the fromUtf8 () 函數。

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.

另請參閱 fromLatin1 (), fromLocal8Bit ()，和 fromUtf8 ().

QString:: QString (const QByteArray & ba )

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.

另請參閱 fromLatin1 (), fromLocal8Bit ()，和 fromUtf8 ().

QString:: QString (const QString & other )

構造副本為 other .

此操作花費 常量時間 ，因為 QString 是 隱式共享 . 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 綫性時間 .

另請參閱 operator= ().

QString:: QString ( QString && other )

Move-constructs a QString instance, making it point at the same object that other 所指嚮的。

QString:: ~QString ()

銷毀字符串。

QString &QString:: append (const QString & str )

追加字符串 str 到此字符串末尾。

範例：

QString x = "free";
QString y = "dom";
x.append(y);
// x == "freedom"
						

這如同使用 insert () 函數：

x.insert(x.size(), y);
						

append() 函數通常非常快 ( 常量時間 )，因為 QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.

另請參閱 operator+= (), prepend ()，和 insert ().

QString &QString:: append ( QChar ch )

此函數重載 append()。

追加字符 ch 到此字符串。

QString &QString:: append (const QChar * str , qsizetype len )

此函數重載 append()。

追加 len 字符來自 QChar array str 到此字符串。

[since 6.0] QString &QString:: append ( QStringView v )

此函數重載 append()。

Appends the given string view v to this string and returns the result.

該函數在 Qt 6.0 引入。

QString &QString:: append ( QLatin1StringView str )

此函數重載 append()。

Appends the Latin-1 string viewed by str 到此字符串。

[since 6.5] QString &QString:: append ( QUtf8StringView str )

此函數重載 append()。

Appends the UTF-8 string view str 到此字符串。

This function was introduced in Qt 6.5.

QString &QString:: append (const char * str )

此函數重載 append()。

追加字符串 str to this string. The given const char pointer is converted to Unicode using the fromUtf8 () 函數。

可以禁用此函數通過定義 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.

QString &QString:: append (const QByteArray & ba )

此函數重載 append()。

追加字節數組 ba to this string. The given byte array is converted to Unicode using the fromUtf8 () 函數。

可以禁用此函數通過定義 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.

QString QString:: arg (const QString & a , int fieldWidth = 0, QChar fillChar = u' ') const

返迴字符串副本，替換最小編號位置標記為字符串 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.

此範例展示如何創建 status 字符串為處理文件列錶時報告進度：

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) 替換 %1 。然後 arg(total) 替換 %2 。最後， arg(fileName) 替換 %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.

QString QString:: arg ( qlonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

此函數重載 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.

另請參閱 Number Formats .

QString QString:: arg ( qulonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

此函數重載 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.

另請參閱 Number Formats .

QString QString:: arg ( long a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

此函數重載 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"
						

另請參閱 Number Formats .

QString QString:: arg ( ulong a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

此函數重載 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.

另請參閱 Number Formats .

QString QString:: arg ( int a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

此函數重載 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"
						

另請參閱 Number Formats .

QString QString:: arg ( uint a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

此函數重載 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.

另請參閱 Number Formats .

QString QString:: arg ( short a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

此函數重載 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.

另請參閱 Number Formats .

QString QString:: arg ( ushort a , int fieldWidth = 0, int base = 10, QChar fillChar = u' ') const

此函數重載 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.

另請參閱 Number Formats .

QString QString:: arg ( double a , int fieldWidth = 0, char format = 'g', int precision = -1, QChar fillChar = u' ') const

此函數重載 arg()。

自變量 a is formatted according to the specified format and precision 。見 Floating-point Formats 瞭解細節。

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"
						

另請參閱 QLocale::toString (), QLocale::FloatingPointPrecisionOption ，和 Number Formats .

QString QString:: arg ( char a , int fieldWidth = 0, QChar fillChar = u' ') const

此函數重載 arg()。

The a 自變量被解釋成 Latin-1 字符。

QString QString:: arg ( QChar a , int fieldWidth = 0, QChar fillChar = u' ') const

此函數重載 arg()。

QString QString:: arg ( QStringView a , int fieldWidth = 0, QChar fillChar = u' ') const

這是重載函數。

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.

此範例展示如何創建 status 字符串為處理文件列錶時報告進度：

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) 替換 %1 。然後 arg(total) 替換 %2 。最後， arg(fileName) 替換 %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.

QString QString:: arg ( QLatin1StringView a , int fieldWidth = 0, QChar fillChar = u' ') const

這是重載函數。

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 , ...)

安全地構建格式化字符串從格式字符串 cformat 和任意自變量列錶。

格式字符串支持轉換說明符、長度修飾符及由標準 C++ 庫 printf() 提供的標誌。 cformat 字符串和 %s 自變量必須是 UTF-8 編碼。

注意： The %lc 轉義序列期望 unicode 字符類型為 char16_t ，或 ushort (如返迴通過 QChar::unicode ())。 %ls 轉義序列期望的指針指嚮以 0 結尾的數組的 Unicode 字符類型為 char16_t ，或 ushort (如返迴通過 QString::utf16 ())。這與標準 C++ 庫 printf() 不一緻，後者定義的 %lc 會打印 wchar_t 而 %ls 會打印 wchar_t* ，且平颱還可能産生編譯器警告，若大小請考慮使用請考慮使用請考慮使用請考慮使用請考考慮 wchar_t 不是 16 位。

警告： 不推薦在新 Qt 代碼中使用 QString::asprintf()。取而代之，考慮使用 QTextStream or arg ()，兩者無縫支持 Unicode 字符串且是類型安全的。這裏的範例使用 QTextStream :

QString result;
QTextStream(&result) << "pi = " << 3.14;
// result == "pi = 3.14"
						

For translations ，尤其當字符串包含多個轉義序列時，應考慮使用 arg () 函數代替。這允許翻譯者控製置換次序。

另請參閱 arg ().

const QChar QString:: at ( qsizetype position ) const

返迴字符按給定索引 position 在字符串中。

The position 在字符串中必須是有效索引位置 (即 0 <= position < size ()).

另請參閱 operator[] ().

QChar QString:: back () const

返迴字符串中的最後一個字符。如同 at(size() - 1) .

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串調用此函數，將構成未定義行為。

另請參閱 front (), at ()，和 operator[] ().

QChar &QString:: back ()

Returns a reference to the last character in the string. Same as operator[](size() - 1) .

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串調用此函數，將構成未定義行為。

另請參閱 front (), at ()，和 operator[] ().

QString::iterator QString:: begin ()

返迴 STL 樣式迭代器 指嚮字符串中的首個字符。

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 constBegin () 和 end ().

QString::const_iterator QString:: begin () const

此函數重載 begin()。

qsizetype QString:: capacity () const

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.

另請參閱 reserve () 和 squeeze ().

QString::const_iterator QString:: cbegin () const

返迴常量 STL 樣式迭代器 指嚮字符串中的首個字符。

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 begin () 和 cend ().

QString::const_iterator QString:: cend () const

返迴常量 STL 樣式迭代器 pointing just after the last character in the string.

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 cbegin () 和 end ().

void QString:: chop ( qsizetype n )

移除 n 個字符從字符串末尾起。

若 n >= size ()，結果為空字符串；若 n 為負，相當於傳遞 0。

範例：

QString str("LOGOUT\r\n");
str.chop(2);
// str == "LOGOUT"
						

若想要移除字符從 beginning 對於字符串，使用 remove () 代替。

另請參閱 truncate (), resize (), remove ()，和 QStringView::chop ().

QString QString:: chopped ( qsizetype len ) const

Returns a string that contains the size () - len leftmost characters of this string.

注意： 行為未定義若 len 為負或大於 size ().

另請參閱 endsWith (), first (), last (), sliced (), chop ()，和 truncate ().

void QString:: clear ()

清零字符串內容，並使之為 null。

另請參閱 resize () 和 isNull ().

[static] int QString:: compare (const QString & s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

比較 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 和空字符串之間的區彆 .

另請參閱 operator== (), operator< (), operator> ()，和 Comparing Strings .

int QString:: compare (const QString & other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 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.

如同 compare(*this, other , cs ).

int QString:: compare ( QLatin1StringView other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 compare()。

如同 compare(*this, other , cs ).

int QString:: compare ( QStringView s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 compare()。

履行比較為此與 s ，使用區分大小寫設置 cs .

int QString:: compare ( QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 compare()。

履行比較為此與 ch ，使用區分大小寫設置 cs .

[static] int QString:: compare (const QString & s1 , QLatin1StringView s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 compare()。

履行比較為 s1 and s2 ，使用區分大小寫設置 cs .

[static] int QString:: compare ( QLatin1StringView s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 compare()。

履行比較為 s1 and s2 ，使用區分大小寫設置 cs .

[static] int QString:: compare (const QString & s1 , QStringView s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 compare()。

[static] int QString:: compare ( QStringView s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 compare()。

QString::const_iterator QString:: constBegin () const

返迴常量 STL 樣式迭代器 指嚮字符串中的首個字符。

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 begin () 和 constEnd ().

const QChar *QString:: constData () const

返迴指針指嚮的數據存儲在 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： 返迴字符串不能以 \0 結尾。使用 size () 以確定數組的長度。

另請參閱 data (), operator[] ()，和 fromRawData ().

QString::const_iterator QString:: constEnd () const

返迴常量 STL 樣式迭代器 pointing just after the last character in the string.

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 constBegin () 和 end ().

bool QString:: contains (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

返迴 true 若此字符串包含齣現的字符串 str ；否則返迴 false .

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

QString str = "Peter Pan";
str.contains("peter", Qt::CaseInsensitive);    // returns true
						

另請參閱 indexOf () 和 count ().

bool QString:: contains ( QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 contains()。

返迴 true 若此字符串包含齣現字符 ch ；否則返迴 false .

bool QString:: contains ( QLatin1StringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 contains()。

返迴 true 若此字符串包含齣現的 latin-1 字符串 str ；否則返迴 false .

bool QString:: contains ( QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 contains()。

返迴 true 若此字符串包含齣現的字符串視圖 str ；否則返迴 false .

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

另請參閱 indexOf () 和 count ().

bool QString:: contains (const QRegularExpression & re , QRegularExpressionMatch * rmatch = nullptr) const

返迴 true 若正則錶達式 re 匹配此字符串中的某些地方；否則返迴 false .

若匹配成功且 rmatch 不是 nullptr ，它還把匹配結果寫入 QRegularExpressionMatch 對象指嚮的 rmatch .

另請參閱 QRegularExpression::match ().

qsizetype QString:: count (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

返迴 (潛在重疊) 齣現數對於字符串 str 在此字符串中。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

另請參閱 contains () 和 indexOf ().

qsizetype QString:: count ( QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 count()。

返迴齣現數對於字符 ch 在字符串中。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

另請參閱 contains () 和 indexOf ().

[since 6.0] qsizetype QString:: count ( QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 count()。

Returns the number of (potentially overlapping) occurrences of the string view str 在此字符串中。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

該函數在 Qt 6.0 引入。

另請參閱 contains () 和 indexOf ().

qsizetype QString:: count (const QRegularExpression & re ) const

此函數重載 count()。

返迴次數對於正則錶達式 re 匹配在字符串中。

由於曆史原因，此函數計算重疊匹配，因此下文範例有 4 個 ana 或 ama 實例：

QString str = "banana and panama";
str.count(QRegularExpression("a[nm]a"));    // returns 4
						

此行為不同於簡單遍曆字符串中的匹配使用 QRegularExpressionMatchIterator .

另請參閱 QRegularExpression::globalMatch ().

QString::const_reverse_iterator QString:: crbegin () const

返迴常量 STL-style reverse iterator pointing to the first character in the string, in reverse order.

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 begin (), rbegin ()，和 rend ().

QString::const_reverse_iterator QString:: crend () const

返迴常量 STL-style reverse iterator pointing just after the last character in the string, in reverse order.

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 end (), rend ()，和 rbegin ().

QChar *QString:: data ()

返迴指針指嚮的數據存儲在 QString . The pointer can be used to access and modify the characters that compose the string.

不像 constData () 和 unicode ()，返迴數據始終以 \0 結尾。

範例：

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，因為它從不導緻 深拷貝 的齣現。

另請參閱 constData () 和 operator[] ().

const QChar *QString:: data () const

這是重載函數。

注意： 返迴字符串不能以 \0 結尾。使用 size () 以確定數組的長度。

另請參閱 fromRawData ().

QString::iterator QString:: end ()

返迴 STL 樣式迭代器 pointing just after the last character in the string.

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 begin () 和 constEnd ().

QString::const_iterator QString:: end () const

此函數重載 end()。

bool QString:: endsWith (const QString & s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

返迴 true 若字符串結尾為 s ；否則返迴 false .

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

QString str = "Bananas";
str.endsWith("anas");         // returns true
str.endsWith("pple");         // returns false
						

另請參閱 startsWith ().

bool QString:: endsWith ( QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 endsWith()。

返迴 true 若字符串結尾為字符串視圖 str ；否則返迴 false .

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

另請參閱 startsWith ().

bool QString:: endsWith ( QLatin1StringView s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 endsWith()。

bool QString:: endsWith ( QChar c , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

返迴 true 若字符串結尾為 c ；否則返迴 false .

此函數重載 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).

This function was introduced in Qt 6.1.

[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"
						

This function was introduced in Qt 6.5.

QString &QString:: fill ( QChar ch , qsizetype size = -1)

將字符串中的每個字符設為字符 ch 。若 size 不同於 -1 (默認)，重置字符串大小到 size 事先。

範例：

QString str = "Berlin";
str.fill('z');
// str == "zzzzzz"
str.fill('A', 2);
// str == "AA"
						

另請參閱 resize ().

[since 6.0] QString QString:: first ( qsizetype n ) const

Returns a string that contains the first n characters of this string.

注意： 行為未定義當 n < 0 or n > size ().

QString x = "Pineapple";
QString y = x.first(4);      // y == "Pine"
						

該函數在 Qt 6.0 引入。

另請參閱 last (), sliced (), startsWith (), chopped (), chop ()，和 truncate ().

[static] QString QString:: fromCFString ( CFStringRef string )

構造新的 QString 包含副本 string CFString.

注意： this function is only available on macOS and iOS.

[static] QString QString:: fromLatin1 (const char * str , qsizetype size )

返迴 QString 初始采用前 size characters of the Latin-1 string str .

若 size is -1 , strlen(str) 被使用，取而代之。

另請參閱 toLatin1 (), fromUtf8 ()，和 fromLocal8Bit ().

[static, since 6.0] QString QString:: fromLatin1 ( QByteArrayView str )

這是重載函數。

返迴 QString 初始采用 Latin-1 字符串 str .

注意： : any null ('\0') bytes in the byte array will be included in this string, converted to Unicode null characters (U+0000).

該函數在 Qt 6.0 引入。

[static] QString QString:: fromLatin1 (const QByteArray & str )

這是重載函數。

返迴 QString 初始采用 Latin-1 字符串 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 )

返迴 QString 初始采用前 size 個字符對於 8 位字符串 str .

若 size is -1 , strlen(str) 被使用，取而代之。

On Unix systems this is equivalent to fromUtf8 (), on Windows the systems current code page is being used.

另請參閱 toLocal8Bit (), fromLatin1 ()，和 fromUtf8 ().

[static, since 6.0] QString QString:: fromLocal8Bit ( QByteArrayView str )

這是重載函數。

返迴 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).

該函數在 Qt 6.0 引入。

[static] QString QString:: fromLocal8Bit (const QByteArray & str )

這是重載函數。

返迴 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 )

構造新的 QString 包含副本 string NSString.

注意： this function is only available on macOS and iOS.

[static] QString QString:: fromRawData (const QChar * unicode , qsizetype size )

構造 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 。這意味著 unicode () will not return a '\0'-terminated string (although utf16 () does, at the cost of copying the raw data).

另請參閱 fromUtf16 () 和 setRawData ().

[static] QString QString:: fromStdString (const std::string & str )

返迴副本為 str string. The given string is converted to Unicode using the fromUtf8 () 函數。

另請參閱 fromLatin1 (), fromLocal8Bit (), fromUtf8 ()，和 QByteArray::fromStdString ().

[static] QString QString:: fromStdU16String (const std::u16string & str )

返迴副本為 str string. The given string is assumed to be encoded in UTF-16.

另請參閱 fromUtf16 (), fromStdWString ()，和 fromStdU32String ().

[static] QString QString:: fromStdU32String (const std::u32string & str )

返迴副本為 str string. The given string is assumed to be encoded in UCS-4.

另請參閱 fromUcs4 (), fromStdWString ()，和 fromStdU16String ().

[static] QString QString:: fromStdWString (const std::wstring & str )

返迴副本為 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).

另請參閱 fromUtf16 (), fromLatin1 (), fromLocal8Bit (), fromUtf8 (), fromUcs4 (), fromStdU16String ()，和 fromStdU32String ().

[static] QString QString:: fromUcs4 (const char32_t * unicode , qsizetype size = -1)

返迴 QString 初始采用前 size characters of the Unicode string unicode (ISO-10646-UCS-4 encoded).

若 size is -1 (default), unicode must be \0'-terminated.

另請參閱 toUcs4 (), fromUtf16 (), utf16 (), setUtf16 (), fromWCharArray ()，和 fromStdU32String ().

[static] QString QString:: fromUtf8 (const char * str , qsizetype size )

返迴 QString 初始采用前 size bytes of the UTF-8 string str .

若 size is -1 , strlen(str) 被使用，取而代之。

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 .

另請參閱 toUtf8 (), fromLatin1 ()，和 fromLocal8Bit ().

[static, since 6.0] QString QString:: fromUtf8 ( QByteArrayView str )

這是重載函數。

返迴 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).

該函數在 Qt 6.0 引入。

[static] QString QString:: fromUtf8 (const QByteArray & str )

這是重載函數。

返迴 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 )

這是重載函數。

This overload is only available when compiling in C++20 mode.

This function was introduced in Qt 6.1.

[static, since 6.0] QString QString:: fromUtf8 (const char8_t * str , qsizetype size )

這是重載函數。

This overload is only available when compiling in C++20 mode.

該函數在 Qt 6.0 引入。

[static] QString QString:: fromUtf16 (const char16_t * unicode , qsizetype size = -1)

返迴 QString 初始采用前 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.

另請參閱 utf16 (), setUtf16 ()，和 fromStdU16String ().

[static] QString QString:: fromWCharArray (const wchar_t * string , qsizetype size = -1)

返迴副本為 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.

另請參閱 fromUtf16 (), fromLatin1 (), fromLocal8Bit (), fromUtf8 (), fromUcs4 ()，和 fromStdWString ().

QChar QString:: front () const

Returns the first character in the string. Same as at(0) .

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串調用此函數，將構成未定義行為。

另請參閱 back (), at ()，和 operator[] ().

QChar &QString:: front ()

Returns a reference to the first character in the string. Same as operator[](0) .

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串調用此函數，將構成未定義行為。

另請參閱 back (), at ()，和 operator[] ().

qsizetype QString:: indexOf ( QLatin1StringView str , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

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.

另請參閱 lastIndexOf (), contains ()，和 count ().

qsizetype QString:: indexOf ( QChar ch , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 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。

qsizetype QString:: indexOf (const QString & str , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

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.

另請參閱 lastIndexOf (), contains ()，和 count ().

qsizetype QString:: indexOf ( QStringView str , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函數重載 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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

若 from is -1, the search starts at the last character; if it is -2, at the next to last character and so on.

另請參閱 QStringView::indexOf (), lastIndexOf (), contains ()，和 count ().

qsizetype QString:: indexOf (const QRegularExpression & re , qsizetype from = 0, QRegularExpressionMatch * rmatch = nullptr) const

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.

若匹配成功且 rmatch 不是 nullptr ，它還把匹配結果寫入 QRegularExpressionMatch 對象指嚮的 rmatch .

範例：

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
						

QString &QString:: insert ( qsizetype position , const QString & str )

插入字符串 str at the given index position 並返迴此字符串的引用。

範例：

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 .

另請參閱 append (), prepend (), replace ()，和 remove ().

QString &QString:: insert ( qsizetype position , QChar ch )

This function overloads insert().

插入 ch at the given index position 在字符串中。

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 .

QString &QString:: insert ( qsizetype position , const QChar * unicode , qsizetype size )

This function overloads insert().

Inserts the first size characters of the QChar array unicode at the given index position 在字符串中。

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 並返迴此字符串的引用。

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 .

該函數在 Qt 6.0 引入。

QString &QString:: insert ( qsizetype position , QLatin1StringView str )

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 .

This function was introduced in Qt 6.5.

QString &QString:: insert ( qsizetype position , const char * str )

This function overloads insert().

Inserts the C string str at the given index position 並返迴此字符串的引用。

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 有定義。

QString &QString:: insert ( qsizetype position , const QByteArray & str )

This function overloads insert().

Interprets the contents of str as UTF-8, inserts the Unicode string it encodes at the given index position 並返迴此字符串的引用。

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 有定義。

bool QString:: isEmpty () const

返迴 true if the string has no characters; otherwise returns false .

範例：

QString().isEmpty();            // returns true
QString("").isEmpty();          // returns true
QString("x").isEmpty();         // returns false
QString("abc").isEmpty();       // returns false
						

另請參閱 size ().

bool QString:: isLower () const

返迴 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.

另請參閱 QChar::toLower () 和 isUpper ().

bool QString:: isNull () const

返迴 true if this string is null; otherwise returns false .

範例：

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 () 函數。

另請參閱 isEmpty ().

bool QString:: isRightToLeft () const

返迴 true if the string is read right to left.

另請參閱 QStringView::isRightToLeft ().

bool QString:: isUpper () const

返迴 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.

另請參閱 QChar::toUpper () 和 isLower ().

bool QString:: isValidUtf16 () const

返迴 true if the string contains valid UTF-16 encoded data, or false 否則。

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.

另請參閱 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： 行為未定義當 n < 0 or n > size ().

QString x = "Pineapple";
QString y = x.last(5);      // y == "apple"
						

該函數在 Qt 6.0 引入。

另請參閱 first (), sliced (), endsWith (), chopped (), chop ()，和 truncate ().

qsizetype QString:: lastIndexOf (const QString & str , qsizetype from , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

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.

返迴 -1，若 str 找不到。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

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.

另請參閱 indexOf (), contains ()，和 count ().

[since 6.3] qsizetype QString:: lastIndexOf ( QChar c , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

This function was introduced in Qt 6.3.

qsizetype QString:: lastIndexOf ( QChar ch , qsizetype from , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

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
						

This function was introduced in Qt 6.2.

另請參閱 indexOf (), contains ()，和 count ().

qsizetype QString:: lastIndexOf ( QLatin1StringView str , qsizetype from , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

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.

返迴 -1，若 str 找不到。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

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.

另請參閱 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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

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
						

This function was introduced in Qt 6.2.

另請參閱 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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

This function was introduced in Qt 6.2.

另請參閱 indexOf (), contains ()，和 count ().

qsizetype QString:: lastIndexOf ( QStringView str , qsizetype from , 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, 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.

返迴 -1，若 str 找不到。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

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.

另請參閱 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.

若匹配成功且 rmatch 不是 nullptr ，它還把匹配結果寫入 QRegularExpressionMatch 對象指嚮的 rmatch .

範例：

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.

This function was introduced in Qt 6.2.

qsizetype QString:: lastIndexOf (const QRegularExpression & re , qsizetype from , QRegularExpressionMatch * rmatch = nullptr) const

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.

返迴 -1，若 re didn't match anywhere.

若匹配成功且 rmatch 不是 nullptr ，它還把匹配結果寫入 QRegularExpressionMatch 對象指嚮的 rmatch .

範例：

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.

QString QString:: left ( qsizetype n ) const

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.

返迴整個字符串若 n >= size ()，或小於 0。

另請參閱 first (), last (), startsWith (), chopped (), chop ()，和 truncate ().

QString QString:: leftJustified ( qsizetype width , QChar fill = u' ', bool truncate = false) const

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"
						

另請參閱 rightJustified ().

qsizetype QString:: length () const

Returns the number of characters in this string. Equivalent to size ().

另請參閱 resize ().

[static] int QString:: localeAwareCompare (const QString & s1 , const QString & s2 )

比較 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.

另請參閱 compare (), QLocale ，和 Comparing Strings .

int QString:: localeAwareCompare (const QString & 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) .

另請參閱 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) .

該函數在 Qt 6.0 引入。

另請參閱 Comparing Strings .

[static, since 6.0] int QString:: localeAwareCompare ( QStringView s1 , QStringView s2 )

This function overloads localeAwareCompare().

比較 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.

該函數在 Qt 6.0 引入。

另請參閱 Comparing Strings .

QString QString:: mid ( qsizetype position , qsizetype n = -1) const

返迴字符串包含 n 個字符對於此字符串，起始於指定 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.

返迴 null 字符串若 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 .

另請參閱 first (), last (), sliced (), chopped (), chop ()，和 truncate ().

QString QString:: normalized ( QString::NormalizationForm mode , QChar::UnicodeVersion version = QChar::Unicode_Unassigned) const

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 根據指定 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.

格式始終使用 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"
						

另請參閱 setNum ().

[static] QString QString:: number ( int n , int base = 10)

這是重載函數。

[static] QString QString:: number ( uint n , int base = 10)

這是重載函數。

[static] QString QString:: number ( ulong n , int base = 10)

這是重載函數。

[static] QString QString:: number ( qlonglong n , int base = 10)

這是重載函數。

[static] QString QString:: number ( qulonglong n , int base = 10)

這是重載函數。

[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.

另請參閱 setNum (), QLocale::toString (), QLocale::FloatingPointPrecisionOption ，和 Number Formats .

QString &QString:: prepend (const QString & str )

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 ( 常量時間 )，因為 QString preallocates extra space at the beginning of the string data, so it can grow without reallocating the entire string each time.

範例：

QString x = "ship";
QString y = "air";
x.prepend(y);
// x == "airship"
						

另請參閱 append () 和 insert ().

QString &QString:: prepend ( QChar ch )

This function overloads prepend().

前置字符 ch 到此字符串。

QString &QString:: prepend (const QChar * str , qsizetype len )

This function overloads prepend().

前置 len 字符來自 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.

該函數在 Qt 6.0 引入。

QString &QString:: prepend ( QLatin1StringView str )

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。

This function was introduced in Qt 6.5.

QString &QString:: prepend (const char * str )

This function overloads prepend().

前置字符串 str to this string. The const char pointer is converted to Unicode using the fromUtf8 () 函數。

可以禁用此函數通過定義 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.

QString &QString:: prepend (const QByteArray & ba )

This function overloads prepend().

前置字節數組 ba to this string. The byte array is converted to Unicode using the fromUtf8 () 函數。

可以禁用此函數通過定義 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.

void QString:: push_back (const QString & other )

This function is provided for STL compatibility, appending the given other string onto the end of this string. It is equivalent to append(other) .

另請參閱 append ().

void QString:: push_back ( QChar ch )

這是重載函數。

Appends the given ch character onto the end of this string.

void QString:: push_front (const QString & other )

This function is provided for STL compatibility, prepending the given other string to the beginning of this string. It is equivalent to prepend(other) .

另請參閱 prepend ().

void QString:: push_front ( QChar ch )

這是重載函數。

Prepends the given ch character to the beginning of this string.

QString::reverse_iterator QString:: rbegin ()

返迴 STL-style reverse iterator pointing to the first character in the string, in reverse order.

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 begin (), crbegin ()，和 rend ().

QString::const_reverse_iterator QString:: rbegin () const

這是重載函數。

QString &QString:: remove ( qsizetype position , qsizetype n )

移除 n characters from the string, starting at the given position index, and returns a reference to the string.

若指定 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.

另請參閱 insert () 和 replace ().

QString &QString:: remove ( QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Removes every occurrence of the character ch in this string, and returns a reference to this string.

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

QString t = "Ali Baba";
t.remove(QChar('a'), Qt::CaseInsensitive);
// t == "li Bb"
						

這如同 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.

另請參閱 replace ().

QString &QString:: remove ( QLatin1StringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive)

這是重載函數。

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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

這如同 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.

另請參閱 replace ().

QString &QString:: remove (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Removes every occurrence of the given str string in this string, and returns a reference to this string.

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

這如同 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.

另請參閱 replace ().

QString &QString:: remove (const QRegularExpression & re )

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.

另請參閱 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.

This function was introduced in Qt 6.5.

另請參閱 remove ().

[since 6.5] QString &QString:: removeFirst ()

Removes the first character in this string. If the string is empty, this function does nothing.

This function was introduced in Qt 6.5.

另請參閱 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.

This function was introduced in Qt 6.1.

另請參閱 remove ().

[since 6.5] QString &QString:: removeLast ()

Removes the last character in this string. If the string is empty, this function does nothing.

This function was introduced in Qt 6.5.

另請參閱 remove ().

QString::reverse_iterator QString:: rend ()

返迴 STL-style reverse iterator pointing just after the last character in the string, in reverse order.

警告： The returned iterator is invalidated on detachment or when the QString 被修改。

另請參閱 end (), crend ()，和 rbegin ().

QString::const_reverse_iterator QString:: rend () const

這是重載函數。

QString QString:: repeated ( qsizetype times ) const

Returns a copy of this string repeated the specified number of times .

若 times is less than 1, an empty string is returned.

範例：

QString str("ab");
str.repeated(4);            // returns "abababab"
						

QString &QString:: replace ( qsizetype position , qsizetype n , const QString & after )

替換 n characters beginning at index position 采用字符串 after 並返迴此字符串的引用。

注意： 若指定 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.

範例：

QString x = "Say yes!";
QString y = "no";
x.replace(4, 3, y);
// x == "Say no!"
						

另請參閱 insert () 和 remove ().

QString &QString:: replace ( qsizetype position , qsizetype n , QChar after )

此函數重載 replace()。

替換 n characters beginning at index position with the character after 並返迴此字符串的引用。

QString &QString:: replace ( qsizetype position , qsizetype n , const QChar * unicode , qsizetype size )

此函數重載 replace()。

替換 n characters beginning at index position with the first size characters of the QChar array unicode 並返迴此字符串的引用。

QString &QString:: replace ( QChar before , QChar after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 replace()。

Replaces every occurrence of the character before with the character after 並返迴此字符串的引用。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

QString &QString:: replace (const QChar * before , qsizetype blen , const QChar * after , qsizetype alen , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 replace()。

Replaces each occurrence in this string of the first blen 字符的 before with the first alen 字符的 after 並返迴此字符串的引用。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

QString &QString:: replace ( QLatin1StringView before , QLatin1StringView after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

注意： The text is not rescanned after a replacement.

QString &QString:: replace ( QLatin1StringView before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 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 (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

注意： The text is not rescanned after a replacement.

QString &QString:: replace (const QString & before , QLatin1StringView after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 replace()。

Replaces every occurrence of the string before 采用字符串 after 並返迴此字符串的引用。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

注意： The text is not rescanned after a replacement.

QString &QString:: replace (const QString & before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 replace()。

Replaces every occurrence of the string before 采用字符串 after 並返迴此字符串的引用。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

範例：

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.

範例：

QString equis = "xxxxxx";
equis.replace("xx", "x");
// equis == "xxx"
						

QString &QString:: replace ( QChar ch , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 replace()。

Replaces every occurrence of the character ch in the string with after 並返迴此字符串的引用。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

QString &QString:: replace ( QChar c , QLatin1StringView after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函數重載 replace()。

Replaces every occurrence of the character c 采用字符串 after 並返迴此字符串的引用。

若 cs is Qt::CaseSensitive (默認)，搜索區分大小寫；否則，搜索不區分大小寫。

注意： The text is not rescanned after a replacement.

QString &QString:: replace (const QRegularExpression & re , const QString & after )

此函數重載 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}."
						

另請參閱 indexOf (), lastIndexOf (), remove (), QRegularExpression ，和 QRegularExpressionMatch .

void QString:: reserve ( qsizetype size )

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();
						

另請參閱 squeeze (), capacity ()，和 resize ().

void QString:: resize ( qsizetype size )

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 ().

範例：

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 () 函數：

若 size 為負，相當於傳遞 0。

QString r = "Hello";
r = r.leftJustified(10, ' ');
// r == "Hello     "
						

另請參閱 truncate (), reserve ()，和 squeeze ().

void QString:: resize ( qsizetype newSize , QChar fillChar )

這是重載函數。

不像 resize (qsizetype), this overload initializes the new characters to fillChar :

QString t = "Hello";
r.resize(t.size() + 10, 'X');
// t == "HelloXXXXXXXXXX"
						

QString QString:: right ( qsizetype n ) const

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.

返迴整個字符串若 n >= size ()，或小於 0。

另請參閱 endsWith (), last (), first (), sliced (), chopped (), chop ()，和 truncate ().

QString QString:: rightJustified ( qsizetype width , QChar fill = u' ', bool truncate = false) const

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"
						

另請參閱 leftJustified ().

QString QString:: section ( QChar sep , qsizetype start , qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const

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"
						

另請參閱 split ().

QString QString:: section (const QString & sep , qsizetype start , qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const

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"
						

另請參閱 split ().

QString QString:: section (const QRegularExpression & re , qsizetype start , qsizetype end = -1, QString::SectionFlags flags = SectionDefault) const

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.

另請參閱 split () 和 simplified ().

QString &QString:: setNum ( int n , int base = 10)

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"
						

格式始終使用 QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.

另請參閱 number ().

QString &QString:: setNum ( short n , int base = 10)

這是重載函數。

QString &QString:: setNum ( ushort n , int base = 10)

這是重載函數。

QString &QString:: setNum ( uint n , int base = 10)

這是重載函數。

QString &QString:: setNum ( long n , int base = 10)

這是重載函數。

QString &QString:: setNum ( ulong n , int base = 10)

這是重載函數。

QString &QString:: setNum ( qlonglong n , int base = 10)

這是重載函數。

QString &QString:: setNum ( qulonglong n , int base = 10)

這是重載函數。

QString &QString:: setNum ( float n , char format = 'g', int precision = 6)

這是重載函數。

Sets the string to the printed value of n , formatted according to the given format and precision , and returns a reference to the string.

格式始終使用 QLocale::C , i.e., English/UnitedStates. To get a localized string representation of a number, use QLocale::toString () with the appropriate locale.

另請參閱 number ().

QString &QString:: setNum ( double n , char format = 'g', int precision = 6)

這是重載函數。

Sets the string to the printed value of n , formatted according to the given format and precision , and returns a reference to the string.

另請參閱 number (), QLocale::FloatingPointPrecisionOption ，和 Number Formats .

QString &QString:: setRawData (const QChar * unicode , qsizetype size )

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.

另請參閱 fromRawData ().

QString &QString:: setUnicode (const QChar * unicode , qsizetype size )

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 .

另請參閱 unicode () 和 setUtf16 ().

QString &QString:: setUtf16 (const ushort * unicode , qsizetype size )

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.

另請參閱 utf16 () 和 setUnicode ().

void QString:: shrink_to_fit ()

此函數為兼容 STL (標準模闆庫) 提供。它相當於 squeeze ().

另請參閱 squeeze ().

QString QString:: simplified () const

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.

空白意味著任何字符其。 QChar::isSpace () 返迴 true 。這包括 ASCII 字符 \t、\n、\v、\f、\r、及 " "。

範例：

QString str = "  lots\t of\nwhitespace\r\n ";
str = str.simplified();
// str == "lots of whitespace";
						

另請參閱 trimmed ().

qsizetype QString:: size () const

Returns the number of characters in this string.

The last character in the string is at position size() - 1.

範例：

QString str = "World";
qsizetype n = str.size();   // n == 5
str.data()[0];              // returns 'W'
str.data()[4];              // returns 'd'
						

另請參閱 isEmpty () 和 resize ().

[since 6.0] QString QString:: sliced ( qsizetype pos , qsizetype n ) const

返迴字符串包含 n characters of this string, starting at position pos .

注意： 行為未定義當 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"
						

該函數在 Qt 6.0 引入。

另請參閱 first (), last (), chopped (), chop ()，和 truncate ().

[since 6.0] QString QString:: sliced ( qsizetype pos ) const

這是重載函數。

Returns a string that contains the portion of this string starting at position pos and extending to its end.