内容

• 公共类型
• 公共函数
• 静态公共成员
• 相关非成员
• 宏
• 详细描述
• 初始化字符串
• 操纵字符串数据
• 查询字符串数据
• 在编码字符串数据和 QString 之间转换
• null 和空字符串之间的区别
• Number Formats
• 更高效的字符串构造
• 最大尺寸和内存不足情况

QString 类

QString 类提供 Unicode 字符串。 更多...

• 所有成员列表，包括继承成员
• 弃用成员

注意： 此类的所有函数 可重入 .

公共类型

公共函数

静态公共成员

相关非成员

宏

详细描述

QString 存储字符串的 16 位 QChar ，其中各 QChar corresponds to one UTF-16 code unit. (Unicode characters with code values above 65535 are stored using surrogate pairs, i.e., two consecutive QChar )。

Unicode 是支持当今使用的大多数书写系统的国际标准。它是 US-ASCII (ANSI X3.4-1986) 和 Latin-1 (ISO 8859-1) 的超集，且所有 US-ASCII/Latin-1 字符可用于相同代码位置。

在幕后，QString 使用 隐式共享 (写时拷贝) 以缩减内存用量并避免不必要的数据拷贝。这还有助于缩减存储 16 位字符而不是 8 位字符的固有开销。

除 QString 外，Qt 还提供 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 是合适的，当需要存储原生二进制数据时，和当内存守恒临界时 (像在嵌入式系统)。

初始化字符串

One way to initialize a QString is simply to pass a const char * 到其构造函数。例如，以下代码创建包含数据 Hello 大小为 5 的 QString：

QString str = "Hello";
					

QString 转换 const char * 数据成 Unicode 使用 fromUtf8 () 函数。

QString 的所有函数都接受 const char * 参数， 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 .

还可以将字符串数据提供成数组化的 QChar ：

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

QString 制作深拷贝对 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.)

另一种方式是设置字符串大小使用 resize () 并逐字符初始化数据。QString 使用基于 0 的索引，就像 C++ 数组。要访问位于特定索引位置的字符，可以使用 operator[] ()。对于非 const 字符串， operator[] () 返回可以用于赋值左侧的字符引用。例如：

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

对于只读访问，替代句法是使用 at () 函数：

QString str;
for (qsizetype i = 0; i < str.size(); ++i) {
    if (str.at(i) >= QChar('a') && str.at(i) <= QChar('f'))
        qDebug() << "Found character in range [a-f]";
}
					

at () 函数可以更快相比 operator[] (), because it never causes a 深拷贝 的出现。另外，使用 first (), last ()，或 sliced () 函数能一次提取几个字符。

QString 可以嵌入 \0 字符 ( QChar::Null )。 size () 函数始终返回整个字符串的大小，包括嵌入 \0 字符。

后于调用 resize () 函数，新近分配字符拥有未定义值。要把字符串中的所有字符设为特定值，使用 fill () 函数。

QString 提供了很多设计用于简化字符串用法的重载。例如，若想要比较 QString 与字符串文字，可以像这样编写代码且它会如期望般工作：

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

还可以把字符串文字传递给接受 QString 作为自变量的函数，援引 QString(const char *) 构造函数。同样，可以传递 QString 的函数接受 const char * 自变量使用 qPrintable () macro which returns the given QString as a const char * 。这相当于调用 <QString>. toLocal8Bit (). constData ().

操纵字符串数据

QString 提供修改字符数据的基本功能： 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 () 函数的前 2 自变量是从哪里开始替换的位置，和应替换的字符数。

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.

insert (), remove () and, when replacing a sub-string with one of different size, replace () 函数可能很慢 ( 线性时间 ) for large strings, because they require moving many characters in the string by at least one position in memory.

若正逐步构建 QString 且提前大概知道 QString 将包含多少个字符，可以调用 reserve ()，要求 QString 预分配一定数量的内存。也可以调用 capacity () 以找出 QString 实际有分配多少内存。

QString 提供 STL 样式迭代器 ( QString::const_iterator and QString::iterator ). In practice, iterators are handy when working with generic algorithms provided by the C++ standard library.

注意： Iterators over a QString, and references to individual characters within one, cannot be relied on to remain valid when any non- const method of the QString is called. Accessing such an iterator or reference after the call to a non- const method leads to undefined behavior. When stability for iterator-like functionality is required, you should use indexes instead of iterators as they are not tied to QString's internal state and thus do not get invalidated.

注意： 由于 隐式共享 , the first non- const operator or function used on a given QString may cause it to, internally, perform a deep copy of its data. This invalidates all iterators over the string and references to individual characters within it. After the first non- const operator, operations that modify QString may completely (in case of reallocation) or partially invalidate iterators and references, but other methods (such as begin () 或 end ()) will not. Accessing an iterator or reference after it has been invalidated leads to undefined behavior.

A frequent requirement is to remove whitespace characters from a string ('\n', '\t', ' ', etc.). If you want to remove whitespace from both ends of a QString, use the trimmed () function. If you want to remove whitespace from both ends and replace multiple consecutive whitespaces with a single space character within the string, use simplified ().

若想要查找 QString 中的特定字符 (或子字符串) 的所有出现，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 提供了很多按数字转换成字符串，和把字符串转换成数字的函数。见 arg () 函数， setNum () 函数， number () 静态函数，和 toInt (), toDouble ()，及类似函数。

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

字符串列表的处理是通过 QStringList 类。可以把字符串分割成字符串列表使用 split () 函数，和把字符串列表联接成单字符串采用可选分隔符使用 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 () 函数。

查询字符串数据

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 ().

要获得实际字符数据指针，调用 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

可以比较 QString 使用重载运算符譬如 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() ,

在编码字符串数据和 QString 之间转换

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

• toLatin1 () 返回 Latin-1 (ISO 8859-1) 编码 8 位字符串。
• toUtf8 () 返回 UTF-8 编码 8 位字符串。UTF-8 是 US-ASCII (ANSI X3.4-1986) 超集，支持透过多字节序列的整个 Unicode 字符集。
• toLocal8Bit () 返回使用系统区域设置编码的 8 位字符串。这如同 toUtf8 () 在 Unix 系统。

要转换自这些编码之一，QString 提供 fromLatin1 (), fromUtf8 ()，和 fromLocal8Bit ()。其它编码的支持是透过 QStringEncoder and QStringDecoder 类。

As mentioned above, QString provides a lot of functions and operators that make it easy to interoperate with const char * strings. But this functionality is a double-edged sword: It makes QString more convenient to use if all strings are US-ASCII or Latin-1, but there is always the risk that an implicit conversion from or to const char * is done using the wrong 8-bit encoding. To minimize these risks, you can turn off these implicit conversions by defining some of the following preprocessor symbols:

• 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 QLatin1String class, for example:

QString url = QLatin1String("https://www.unicode.org/");
					

同样，必须调用 toLatin1 (), toUtf8 ()，或 toLocal8Bit () 明确把 QString 转换成 8 位字符串。

QString Widget::boolToString(bool b)
{


QString


 result;

if

 (b)
result

=


"True"

;

else

result

=


"False"

;

return

 result;
}
								

null 和空字符串之间的区别

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
						

所有函数除了 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

当 QString::arg () '%' 格式说明符包括 'L' locale qualifier, and the base is ten (its default), the default locale is used. This can be set using QLocale::setDefault (). For more refined control of localized string representations of numbers, see QLocale::toString (). All other number formatting done by QString follows the C locale's representation of numbers.

当 QString::arg () applies left-padding to numbers, the fill character '0' is treated specially. If the number is negative, its minus sign will appear before the zero-padding. If the field is localized, the locale-appropriate zero character is used in place of '0' . For floating-point numbers, this special treatment only applies if the number is finite.

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).

若选中 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.

更高效的字符串构造

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 QLatin1String . 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 = QLatin1String("vector<") + type + QLatin1String(">::iterator");
    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 () 需要额外测试)。

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 '%' 运算符而不是 '+' 当串联字符串时：

    #include <QStringBuilder>
    QString hello("hello");
    QStringView el = QStringView{ hello }.mid(2, 3);
    QLatin1String 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:

    DEFINES *= QT_USE_QSTRINGBUILDER
						

和 '+' will automatically be performed as the QStringBuilder '%' everywhere.

最大尺寸和内存不足情况

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 .

当内存分配失败时，QString 抛出 std::bad_alloc exception if the application was compiled with exception support. Out of memory conditions in Qt containers are the only case where Qt will throw exceptions. If exceptions are disabled, then running out of memory is undefined behavior.

Note that the operating system may impose further limits on applications holding a lot of allocated memory, especially large, contiguous blocks. Such considerations, the configuration of such behavior or any mitigation are outside the scope of the Qt API.

另请参阅 fromRawData (), QChar , QStringView , QLatin1String ，和 QByteArray .

成员类型文档编制

QString:: ConstIterator

Qt 样式同义词 QString::const_iterator .

QString:: Iterator

Qt 样式同义词 QString::iterator .

enum QString:: NormalizationForm

此枚举描述 Unicode 文本的各种规范化形式。

另请参阅 normalized () 和 Unicode 标准附录 #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 类型是 typedef 对于 QFlags <SectionFlag>. It stores an OR combination of SectionFlag values.

另请参阅 section ().

QString:: const_iterator

另请参阅 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

[since 5.6] QString:: const_reverse_iterator

该 typedef 在 Qt 5.6 引入。

另请参阅 QString::reverse_iterator and QString::const_iterator .

QString:: difference_type

QString:: iterator

另请参阅 QString::const_iterator .

QString:: pointer

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

QString:: reference

[since 5.6] QString:: reverse_iterator

该 typedef 在 Qt 5.6 引入。

另请参阅 QString::const_reverse_iterator and QString::iterator .

QString:: size_type

QString:: value_type

成员函数文档编制

[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 (* this , std::forward < Needle >( needle ), flags ...)) QString:: tokenize ( Needle && sep , Flags ... flags ) const &

Splits the string into substring views wherever sep occurs, and returns a lazy sequence of those strings.

相当于

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

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

见 QStringTokenizer for how sep and flags interact to form the result.

注意： While this function returns QStringTokenizer , you should never, ever, name its template arguments explicitly. If you can use C++17 Class Template Argument Deduction (CTAD), you may write

QStringTokenizer result = sv.tokenize(sep);
						

(without template arguments). If you can't use C++17 CTAD, you must store the return value only in auto 变量：

auto result = sv.tokenize(sep);
						

This is because the template arguments of QStringTokenizer have a very subtle dependency on the specific tokenize () overload from which they are returned, and they don't usually correspond to the type used for the separator.

该函数在 Qt 6.0 引入。

另请参阅 QStringTokenizer and qTokenize ().

[since 5.14] 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 替换 %N with the lowest N (all of them), the second of the args %N with the next-lowest N etc.

Args can consist of anything that implicitly converts to QString , QStringView or QLatin1String .

In addition, the following types are also supported: QChar , QLatin1Char .

该函数在 Qt 5.14 引入。

另请参阅 QString::arg ().

QString:: QString (const QByteArray & ba )

Constructs a string initialized with the byte array ba . The given byte array is converted to Unicode using fromUtf8 (). Stops copying at the first 0 character, otherwise copies the entire byte array.

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.

另请参阅 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 () 函数。

You can disable this constructor by defining QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

注意： Defining QT_RESTRICTED_CAST_FROM_ASCII also disables this constructor, but enables a QString(const char (&ch)[N]) constructor instead. Using non-literal input, or input with embedded NUL characters, or non-7-bit characters is undefined in this case.

另请参阅 fromLatin1 (), fromLocal8Bit ()，和 fromUtf8 ().

[since 5.2] QString:: QString ( QString && other )

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

该函数在 Qt 5.2 引入。

QString:: QString (const QString & other )

构造副本为 other .

此操作花费 常量时间 ，因为 QString 是 隐式共享 . This makes returning a QString from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and that takes 线性时间 .

另请参阅 operator= ().

[since 6.1] template <typename> QString:: QString (const char8_t * str )

Constructs a string initialized with the UTF-8 string str . The given const char8_t pointer is converted to Unicode using the fromUtf8 () 函数。

该函数在 Qt 6.1 引入。

另请参阅 fromLatin1 (), fromLocal8Bit ()，和 fromUtf8 ().

QString:: QString ( QLatin1String str )

Constructs a copy of the Latin-1 string str .

另请参阅 fromLatin1 ().

QString:: QString ( qsizetype size , QChar ch )

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

另请参阅 fill ().

QString:: QString ( QChar ch )

Constructs a string of size 1 containing the character ch .

QString:: QString (const QChar * unicode , qsizetype size = -1)

Constructs a string initialized with the first size characters of the QChar array unicode .

若 unicode 为 0，构造 null 字符串。

若 size 为负， unicode is assumed to point to a \0'-terminated array and its length is determined dynamically. The terminating null character is not considered part of the string.

QString makes a deep copy of the string data. The unicode data is copied as is and the Byte Order Mark is preserved if present.

另请参阅 fromRawData ().

QString:: QString ()

Constructs a null string. Null strings are also empty.

另请参阅 isEmpty ().

QString &QString:: operator= (const QByteArray & ba )

此函数重载 operator=()。

赋值 ba to this string. The byte array is converted to Unicode using the fromUtf8 () function. This function stops conversion at the first NUL character found, or the end of the ba byte array.

可以禁用此运算符通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

[since 5.2] QString &QString:: operator= ( QString && other )

移动赋值 other 到此 QString 实例。

该函数在 Qt 5.2 引入。

QString &QString:: operator= (const QString & other )

赋值 other to this string and returns a reference to this string.

QString:: ~QString ()

销毁字符串。

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

追加字符串 str 到此字符串末尾。

范例：

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

这如同使用 insert () 函数：

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

append() 函数通常非常快 ( 常量时间 )，因为 QString preallocates extra space at the end of the string data so it can grow without reallocating the entire string each time.

另请参阅 operator+= (), prepend ()，和 insert ().

QString &QString:: append ( QChar ch )

此函数重载 append()。

追加字符 ch 到此字符串。

[since 5.0] QString &QString:: append (const QChar * str , qsizetype len )

此函数重载 append()。

追加 len 字符来自 QChar array str 到此字符串。

该函数在 Qt 5.0 引入。

QString &QString:: append ( QLatin1String str )

此函数重载 append()。

追加 Latin-1 字符串 str 到此字符串。

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

此函数重载 append()。

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

可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

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

此函数重载 append()。

追加字节数组 ba to this string. The given byte array is converted to Unicode using the fromUtf8 () 函数。

可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

QString QString:: arg (const QString & a , int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const

返回字符串副本，替换最小编号位置标记为字符串 a ，即： %1 , %2 , ..., %99 .

fieldWidth specifies the minimum amount of space that argument a shall occupy. If a requires less space than fieldWidth , it is padded to fieldWidth with character fillChar . A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.

此范例展示如何创建 status 字符串为处理文件列表时报告进度：

QString i;           // current file's number
QString total;       // number of files to process
QString fileName;    // current file's name
QString status = QString("Processing file %1 of %2: %3")
                .arg(i).arg(total).arg(fileName);
						

首先， arg(i) 替换 %1 。然后 arg(total) 替换 %2 。最后， arg(fileName) 替换 %3 .

One advantage of using arg() over asprintf () is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest numbered unreplaced place marker, no matter where it appears. Also, if place marker %i appears more than once in the string, the arg() replaces all of them.

If there is no unreplaced place marker remaining, a warning message is output and the result is undefined. Place marker numbers must be in the range 1 to 99.

QString QString:: arg ( qlonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

另请参阅 Number Formats .

QString QString:: arg ( qulonglong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a into a string. base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

另请参阅 Number Formats .

QString QString:: arg ( long a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

a argument is expressed in the given base , which is 10 by default and must be between 2 and 36.

The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a . The conversion uses the default locale. The default locale is determined from the system's locale settings at application startup. It can be changed using QLocale::setDefault (). The 'L' flag is ignored if base is not 10.

QString str;
str = QString("Decimal 63 is %1 in hexadecimal")
        .arg(63, 0, 16);
// str == "Decimal 63 is 3f in hexadecimal"
QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates));
str = QString("%1 %L2 %L3")
        .arg(12345)
        .arg(12345)
        .arg(12345, 0, 16);
// str == "12345 12,345 3039"
						

另请参阅 Number Formats .

QString QString:: arg ( ulong a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a to a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

另请参阅 Number Formats .

QString QString:: arg ( int a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

a argument is expressed in base base , which is 10 by default and must be between 2 and 36. For bases other than 10, a is treated as an unsigned integer.

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

The '%' can be followed by an 'L', in which case the sequence is replaced with a localized representation of a . The conversion uses the default locale, set by QLocale::setDefault (). If no default locale was specified, the system locale is used. The 'L' flag is ignored if base is not 10.

QString str;
str = QString("Decimal 63 is %1 in hexadecimal")
        .arg(63, 0, 16);
// str == "Decimal 63 is 3f in hexadecimal"
QLocale::setDefault(QLocale(QLocale::English, QLocale::UnitedStates));
str = QString("%1 %L2 %L3")
        .arg(12345)
        .arg(12345)
        .arg(12345, 0, 16);
// str == "12345 12,345 3039"
						

另请参阅 Number Formats .

QString QString:: arg ( uint a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36.

另请参阅 Number Formats .

QString QString:: arg ( short a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

另请参阅 Number Formats .

QString QString:: arg ( ushort a , int fieldWidth = 0, int base = 10, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

base argument specifies the base to use when converting the integer a into a string. The base must be between 2 and 36, with 8 giving octal, 10 decimal, and 16 hexadecimal numbers.

另请参阅 Number Formats .

QString QString:: arg ( double a , int fieldWidth = 0, char format = 'g', int precision = -1, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

自变量 a is formatted according to the specified format and precision 。见 Floating-point Formats 了解细节。

fieldWidth specifies the minimum amount of space that a is padded to and filled with the character fillChar . A positive value produces right-aligned text; a negative value produces left-aligned text.

double d = 12.34;
QString str = QString("delta: %1").arg(d, 0, 'E', 3);
// str == "delta: 1.234E+01"
						

另请参阅 QLocale::toString (), QLocale::FloatingPointPrecisionOption ，和 Number Formats .

QString QString:: arg ( char a , int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

a 自变量被解释成 Latin-1 字符。

QString QString:: arg ( QChar a , int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const

此函数重载 arg()。

[since 5.10] QString QString:: arg ( QStringView a , int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const

这是重载函数。

Returns a copy of this string with the lowest-numbered place-marker replaced by string a ，即： %1 , %2 , ..., %99 .

fieldWidth specifies the minimum amount of space that a shall occupy. If a requires less space than fieldWidth , it is padded to fieldWidth with character fillChar . A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.

此范例展示如何创建 status 字符串为处理文件列表时报告进度：

int i;                // current file's number
int total;            // number of files to process
QStringView fileName; // current file's name
QString status = QString("Processing file %1 of %2: %3")
                .arg(i).arg(total).arg(fileName);
						

首先， arg(i) 替换 %1 。然后 arg(total) 替换 %2 。最后， arg(fileName) 替换 %3 .

One advantage of using arg() over asprintf () is that the order of the numbered place markers can change, if the application's strings are translated into other languages, but each arg() will still replace the lowest-numbered unreplaced place-marker, no matter where it appears. Also, if place-marker %i appears more than once in the string, arg() replaces all of them.

If there is no unreplaced place-marker remaining, a warning message is printed and the result is undefined. Place-marker numbers must be in the range 1 to 99.

该函数在 Qt 5.10 引入。

[since 5.10] QString QString:: arg ( QLatin1String a , int fieldWidth = 0, QChar fillChar = QLatin1Char(' ')) const

这是重载函数。

Returns a copy of this string with the lowest-numbered place-marker replaced by string a ，即： %1 , %2 , ..., %99 .

fieldWidth specifies the minimum amount of space that a shall occupy. If a requires less space than fieldWidth , it is padded to fieldWidth with character fillChar . A positive fieldWidth produces right-aligned text. A negative fieldWidth produces left-aligned text.

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.

该函数在 Qt 5.10 引入。

[static, since 5.5] QString QString:: asprintf (const char * cformat , ...)

安全地构建格式化字符串从格式字符串 cformat 和任意自变量列表。

格式字符串支持转换说明符、长度修饰符及由标准 C++ 库 printf() 提供的标志。 cformat 字符串和 %s 自变量必须是 UTF-8 编码。

注意： %lc 转义序列期望 unicode 字符类型为 char16_t ，或 ushort (如返回通过 QChar::unicode ())。 %ls 转义序列期望的指针指向以 0 结尾的数组的 Unicode 字符类型为 char16_t ，或 ushort (如返回通过 QString::utf16 ())。这与标准 C++ 库 printf() 不一致，后者定义的 %lc 会打印 wchar_t 而 %ls 会打印 wchar_t* ，且平台还可能产生编译器警告，若大小请考虑使用请考虑使用请考虑使用请考虑使用请考考虑 wchar_t 不是 16 位。

警告： 不推荐在新 Qt 代码中使用 QString::asprintf()。取而代之，考虑使用 QTextStream or arg ()，两者无缝支持 Unicode 字符串且是类型安全的。这里的范例使用 QTextStream :

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

For translations ，尤其当字符串包含多个转义序列时，应考虑使用 arg () 函数代替。这允许翻译者控制置换次序。

该函数在 Qt 5.5 引入。

另请参阅 arg ().

const QChar QString:: at ( qsizetype position ) const

返回字符按给定索引 position 在字符串中。

position must be a valid index position in the string (i.e., 0 <= position < size ()).

另请参阅 operator[] ().

[since 5.10] QChar QString:: back () const

返回字符串中的最后一个字符。如同 at(size() - 1) .

此函数为兼容 STL (标准模板库) 提供。

警告： 在空字符串调用此函数，将构成未定义行为。

该函数在 Qt 5.10 引入。

另请参阅 front (), at ()，和 operator[] ().

[since 5.10] QChar &QString:: back ()

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

此函数为兼容 STL (标准模板库) 提供。

警告： 在空字符串调用此函数，将构成未定义行为。

该函数在 Qt 5.10 引入。

另请参阅 front (), at ()，和 operator[] ().

QString::iterator QString:: begin ()

返回 STL 样式迭代器 指向字符串中的首个字符。

警告： 返回迭代器不验证当分离时或当 QString 被修改。

另请参阅 constBegin () 和 end ().

QString::const_iterator QString:: begin () const

此函数重载 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.

另请参阅 reserve () 和 squeeze ().

[since 5.0] QString::const_iterator QString:: cbegin () const

返回常量 STL 样式迭代器 指向字符串中的首个字符。

警告： 返回迭代器不验证当分离时或当 QString 被修改。

该函数在 Qt 5.0 引入。

另请参阅 begin () 和 cend ().

[since 5.0] QString::const_iterator QString:: cend () const

返回常量 STL 样式迭代器 仅仅指向字符串中最后一个字符的后面。

警告： 返回迭代器不验证当分离时或当 QString 被修改。

该函数在 Qt 5.0 引入。

另请参阅 cbegin () 和 end ().

void QString:: chop ( qsizetype n )

移除 n 个字符从字符串末尾起。

若 n >= size ()，结果为空字符串；若 n 为负，相当于传递 0。

范例：

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

若想要移除字符从 beginning 对于字符串，使用 remove () 代替。

另请参阅 truncate (), resize (), remove ()，和 QStringView::chop ().

[since 5.10] QString QString:: chopped ( qsizetype len ) const

返回字符串包含 size () - len leftmost characters of this string.

注意： 行为未定义若 len 为负或大于 size ().

该函数在 Qt 5.10 引入。

另请参阅 endsWith (), first (), last (), sliced (), chop ()，和 truncate ().

void QString:: clear ()

清零字符串内容，并使之为 null。

另请参阅 resize () 和 isNull ().

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

比较 s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .

若 cs is Qt::CaseSensitive , the 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
						

另请参阅 operator== (), operator< (), operator> ()，和 Comparing Strings .

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

此函数重载 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 ( QLatin1String other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 compare()。

如同 compare(*this, other , cs ).

[since 5.12] int QString:: compare ( QStringView s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 compare()。

履行比较为此与 s ，使用区分大小写设置 cs .

该函数在 Qt 5.12 引入。

[since 5.14] int QString:: compare ( QChar ch , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 compare()。

履行比较为此与 ch ，使用区分大小写设置 cs .

该函数在 Qt 5.14 引入。

[static] int QString:: compare (const QString & s1 , QLatin1String s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函数重载 compare()。

履行比较为 s1 and s2 ，使用区分大小写设置 cs .

[static] int QString:: compare ( QLatin1String s1 , const QString & s2 , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函数重载 compare()。

履行比较为 s1 and s2 ，使用区分大小写设置 cs .

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

此函数重载 compare()。

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

此函数重载 compare()。

QString::const_iterator QString:: constBegin () const

返回常量 STL 样式迭代器 指向字符串中的首个字符。

警告： 返回迭代器不验证当分离时或当 QString 被修改。

另请参阅 begin () 和 constEnd ().

const QChar *QString:: constData () const

返回指针指向的数据存储在 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： 返回字符串不能以 \0 结尾。使用 size () 以确定数组的长度。

另请参阅 data (), operator[] ()，和 fromRawData ().

QString::const_iterator QString:: constEnd () const

返回常量 STL 样式迭代器 仅仅指向字符串中最后一个字符的后面。

警告： 返回迭代器不验证当分离时或当 QString 被修改。

另请参阅 constBegin () 和 end ().

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

返回 true 若此字符串包含出现的字符串 str ；否则返回 false .

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

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

另请参阅 indexOf () 和 count ().

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

此函数重载 contains()。

返回 true 若此字符串包含出现字符 ch ；否则返回 false .

[since 5.3] bool QString:: contains ( QLatin1String str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 contains()。

返回 true 若此字符串包含出现的 latin-1 字符串 str ；否则返回 false .

该函数在 Qt 5.3 引入。

[since 5.14] bool QString:: contains ( QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 contains()。

返回 true 若此字符串包含出现的字符串视图 str ；否则返回 false .

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

该函数在 Qt 5.14 引入。

另请参阅 indexOf () 和 count ().

[since 5.1] bool QString:: contains (const QRegularExpression & re , QRegularExpressionMatch * rmatch = nullptr) const

返回 true 若正则表达式 re 匹配此字符串中的某些地方；否则返回 false .

若匹配成功且 rmatch 不是 nullptr ，它还把匹配结果写入 QRegularExpressionMatch 对象指向的 rmatch .

该函数在 Qt 5.1 引入。

另请参阅 QRegularExpression::match ().

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

返回 (潜在重叠) 出现数对于字符串 str 在此字符串中。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

另请参阅 contains () 和 indexOf ().

qsizetype QString:: count () const

此函数重载 count()。

如同 size ().

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

此函数重载 count()。

返回出现数对于字符 ch 在字符串中。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

另请参阅 contains () 和 indexOf ().

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

此函数重载 count()。

返回 (潜在重叠) 出现数对于字符串视图 str 在此字符串中。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

该函数在 Qt 6.0 引入。

另请参阅 contains () 和 indexOf ().

[since 5.0] qsizetype QString:: count (const QRegularExpression & re ) const

此函数重载 count()。

返回次数对于正则表达式 re 匹配在字符串中。

由于历史原因，此函数计算重叠匹配，因此下文范例有 4 个 ana 或 ama 实例：

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

此行为不同于简单遍历字符串中的匹配使用 QRegularExpressionMatchIterator .

该函数在 Qt 5.0 引入。

另请参阅 QRegularExpression::globalMatch ().

[since 5.6] QString::const_reverse_iterator QString:: crbegin () const

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

警告： 返回迭代器不验证当分离时或当 QString 被修改。

该函数在 Qt 5.6 引入。

另请参阅 begin (), rbegin ()，和 rend ().

[since 5.6] QString::const_reverse_iterator QString:: crend () const

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

警告： 返回迭代器不验证当分离时或当 QString 被修改。

该函数在 Qt 5.6 引入。

另请参阅 end (), rend ()，和 rbegin ().

QChar *QString:: data ()

返回指针指向的数据存储在 QString . The pointer can be used to access and modify the characters that compose the string.

不像 constData () 和 unicode ()，返回数据始终以 \0 结尾。

范例：

QString str = "Hello world";
QChar *data = str.data();
while (!data->isNull()) {
    qDebug() << data->unicode();
    ++data;
}
						

Note that the pointer remains valid only as long as the string is not modified by other means. For read-only access, constData () 更快，因为它从不导致 深拷贝 的出现。

另请参阅 constData () 和 operator[] ().

const QChar *QString:: data () const

这是重载函数。

注意： 返回字符串不能以 \0 结尾。使用 size () 以确定数组的长度。

另请参阅 fromRawData ().

QString::iterator QString:: end ()

返回 STL 样式迭代器 仅仅指向字符串中最后一个字符的后面。

警告： 返回迭代器不验证当分离时或当 QString 被修改。

另请参阅 begin () 和 constEnd ().

QString::const_iterator QString:: end () const

此函数重载 end()。

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

返回 true 若字符串结尾为 s ；否则返回 false .

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

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

另请参阅 startsWith ().

[since 5.10] bool QString:: endsWith ( QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 endsWith()。

返回 true 若字符串结尾为字符串视图 str ；否则返回 false .

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

该函数在 Qt 5.10 引入。

另请参阅 startsWith ().

bool QString:: endsWith ( QLatin1String s , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 endsWith()。

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

返回 true 若字符串结尾为 c ；否则返回 false .

此函数重载 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 referred to by last before the erase.

该函数在 Qt 6.1 引入。

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

将字符串中的每个字符设为字符 ch 。若 size 不同于 -1 (默认)，重置字符串大小到 size 事先。

范例：

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

另请参阅 resize ().

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

返回字符串包含前 n 个字符对于此字符串。

注意： 行为未定义当 n < 0 or n > size ().

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

该函数在 Qt 6.0 引入。

另请参阅 last (), sliced (), startsWith (), chopped (), chop ()，和 truncate ().

[static, since 5.2] QString QString:: fromCFString ( CFStringRef string )

构造新的 QString 包含副本 string CFString.

注意： 此函数只可用于 macOS 和 iOS。

该函数在 Qt 5.2 引入。

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

返回 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。

另请参阅 toLatin1 (), fromUtf8 ()，和 fromLocal8Bit ().

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

这是重载函数。

返回 QString 初始采用 Latin-1 字符串 str .

该函数在 Qt 6.0 引入。

[static, since 5.0] template <typename> QString QString:: fromLatin1 (const QByteArray & str )

这是重载函数。

返回 QString 初始采用 Latin-1 字符串 str .

该函数在 Qt 5.0 引入。

[static] QString QString:: fromLocal8Bit (const char * str , qsizetype size )

返回 QString 初始采用前 size 个字符对于 8 位字符串 str .

若 size is -1 , strlen(str) 被使用，取而代之。

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

另请参阅 toLocal8Bit (), fromLatin1 ()，和 fromUtf8 ().

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

这是重载函数。

返回 QString initialized with the 8-bit string str .

该函数在 Qt 6.0 引入。

[static, since 5.0] template <typename> QString QString:: fromLocal8Bit (const QByteArray & str )

这是重载函数。

返回 QString initialized with the 8-bit string str .

该函数在 Qt 5.0 引入。

[static, since 5.2] QString QString:: fromNSString (const NSString * string )

构造新的 QString 包含副本 string NSString.

注意： 此函数只可用于 macOS 和 iOS。

该函数在 Qt 5.2 引入。

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

构造 QString that uses the first size Unicode characters in the array unicode . The data in unicode is not copied. The caller must be able to guarantee that unicode will not be deleted or modified as long as the QString (or an unmodified copy of it) exists.

Any attempts to modify the QString or copies of it will cause it to create a deep copy of the data, ensuring that the raw data isn't modified.

Here is an example of how we can use a QRegularExpression on raw data in memory without requiring to copy the data into a QString :

QRegularExpression pattern("\u00A4");
static const QChar unicode[] = {
        0x005A, 0x007F, 0x00A4, 0x0060,
        0x1009, 0x0020, 0x0020};
qsizetype size = sizeof(unicode) / sizeof(QChar);
QString str = QString::fromRawData(unicode, size);
if (str.contains(pattern) {
    // ...
}
						

警告： A string created with fromRawData() is not '\0'-terminated, unless the raw data contains a '\0' character at position size 。这意味着 unicode () will not return a '\0'-terminated string (although utf16 () does, at the cost of copying the raw data).

另请参阅 fromUtf16 () 和 setRawData ().

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

返回副本为 str string. The given string is converted to Unicode using the fromUtf8 () 函数。

另请参阅 fromLatin1 (), fromLocal8Bit (), fromUtf8 ()，和 QByteArray::fromStdString ().

[static, since 5.5] QString QString:: fromStdU16String (const std::u16string & str )

返回副本为 str string. The given string is assumed to be encoded in UTF-16.

该函数在 Qt 5.5 引入。

另请参阅 fromUtf16 (), fromStdWString ()，和 fromStdU32String ().

[static, since 5.5] QString QString:: fromStdU32String (const std::u32string & str )

返回副本为 str string. The given string is assumed to be encoded in UCS-4.

该函数在 Qt 5.5 引入。

另请参阅 fromUcs4 (), fromStdWString ()，和 fromStdU16String ().

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

返回副本为 str string. The given string is assumed to be encoded in utf16 if the size of wchar_t is 2 bytes (e.g. on windows) and ucs4 if the size of wchar_t is 4 bytes (most Unix systems).

另请参阅 fromUtf16 (), fromLatin1 (), fromLocal8Bit (), fromUtf8 (), fromUcs4 (), fromStdU16String ()，和 fromStdU32String ().

[static, since 5.3] QString QString:: fromUcs4 (const char32_t * unicode , qsizetype size = -1)

返回 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.

该函数在 Qt 5.3 引入。

另请参阅 toUcs4 (), fromUtf16 (), utf16 (), setUtf16 (), fromWCharArray ()，和 fromStdU32String ().

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

返回 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 .

另请参阅 toUtf8 (), fromLatin1 ()，和 fromLocal8Bit ().

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

这是重载函数。

返回 QString initialized with the UTF-8 string str .

该函数在 Qt 6.0 引入。

[static, since 5.0] template <typename> QString QString:: fromUtf8 (const QByteArray & str )

这是重载函数。

返回 QString initialized with the UTF-8 string str .

该函数在 Qt 5.0 引入。

[static, since 6.1] template <typename> QString QString:: fromUtf8 (const char8_t * str )

这是重载函数。

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

该函数在 Qt 6.1 引入。

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

这是重载函数。

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

该函数在 Qt 6.0 引入。

[static, since 5.3] QString QString:: fromUtf16 (const char16_t * unicode , qsizetype size = -1)

返回 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 *, int) or QString (const QChar *) if possible.

QString makes a deep copy of the Unicode data.

该函数在 Qt 5.3 引入。

另请参阅 utf16 (), setUtf16 ()，和 fromStdU16String ().

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

返回副本为 string , where the encoding of string depends on the size of wchar. If wchar is 4 bytes, the string is interpreted as UCS-4, if wchar is 2 bytes it is interpreted as UTF-16.

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

另请参阅 fromUtf16 (), fromLatin1 (), fromLocal8Bit (), fromUtf8 (), fromUcs4 ()，和 fromStdWString ().

[since 5.10] QChar QString:: front () const

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

此函数为兼容 STL (标准模板库) 提供。

警告： 在空字符串调用此函数，将构成未定义行为。

该函数在 Qt 5.10 引入。

另请参阅 back (), at ()，和 operator[] ().

[since 5.10] QChar &QString:: front ()

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

此函数为兼容 STL (标准模板库) 提供。

警告： 在空字符串调用此函数，将构成未定义行为。

该函数在 Qt 5.10 引入。

另请参阅 back (), at ()，和 operator[] ().

qsizetype QString:: indexOf ( QLatin1String 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 (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

QString x = "sticky question";
QString y = "sti";
x.indexOf(y);               // returns 0
x.indexOf(y, 1);            // returns 10
x.indexOf(y, 10);           // returns 10
x.indexOf(y, 11);           // returns -1
						

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

另请参阅 lastIndexOf (), contains ()，和 count ().

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

此函数重载 indexOf()。

Returns the index position of the first occurrence of the character ch in the string, searching forward from index position from . Returns -1 if ch could not be found.

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 (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

QString x = "sticky question";
QString y = "sti";
x.indexOf(y);               // returns 0
x.indexOf(y, 1);            // returns 10
x.indexOf(y, 10);           // returns 10
x.indexOf(y, 11);           // returns -1
						

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

另请参阅 lastIndexOf (), contains ()，和 count ().

[since 5.14] qsizetype QString:: indexOf ( QStringView str , qsizetype from = 0, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 indexOf()。

Returns the index position of the first occurrence of the string view str in this string, searching forward from index position from . Returns -1 if str 找不到。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

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

该函数在 Qt 5.14 引入。

另请参阅 QStringView::indexOf (), lastIndexOf (), contains ()，和 count ().

[since 5.5] 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 ，它还把匹配结果写入 QRegularExpressionMatch 对象指向的 rmatch .

范例：

QString str = "the minimum";
str.indexOf(QRegularExpression("m[aeiou]"), 0);       // returns 4
QString str = "the minimum";
QRegularExpressionMatch match;
str.indexOf(QRegularExpression("m[aeiou]"), 0, &match);       // returns 4
// match.captured() == mi
						

该函数在 Qt 5.5 引入。

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

插入字符串 str at the given index position 并返回此字符串的引用。

范例：

QString str = "Meal";
str.insert(1, QString("ontr"));
// str == "Montreal"
						

This string grows to accommodate the insertion. If position is beyond the end of the string, space characters are appended to the string to reach this position , followed by str .

另请参阅 append (), prepend (), replace ()，和 remove ().

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 并返回此字符串的引用。

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 .

该函数在 Qt 6.0 引入。

QString &QString:: insert ( qsizetype position , QLatin1String str )

This function overloads insert().

Inserts the Latin-1 string 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 5.5] QString &QString:: insert ( qsizetype position , const char * str )

This function overloads insert().

Inserts the C string str at the given index position 并返回此字符串的引用。

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 有定义。

该函数在 Qt 5.5 引入。

[since 5.5] 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 并返回此字符串的引用。

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 有定义。

该函数在 Qt 5.5 引入。

bool QString:: isEmpty () const

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

范例：

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

另请参阅 size ().

[since 5.12] bool QString:: isLower () const

返回 true if the string is lowercase, that is, it's identical to its toLower () folding.

Note that this does not mean that the string does not contain uppercase letters (some uppercase letters do not have a lowercase folding; they are left unchanged by toLower ()). For more information, refer to the Unicode standard, section 3.13.

该函数在 Qt 5.12 引入。

另请参阅 QChar::toLower () 和 isUpper ().

bool QString:: isNull () const

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

范例：

QString().isNull();             // returns true
QString("").isNull();           // returns false
QString("abc").isNull();        // returns false
						

Qt makes a distinction between null strings and empty strings for historical reasons. For most applications, what matters is whether or not a string contains any data, and this can be determined using the isEmpty () 函数。

另请参阅 isEmpty ().

bool QString:: isRightToLeft () const

返回 true if the string is read right to left.

另请参阅 QStringView::isRightToLeft ().

[since 5.12] bool QString:: isUpper () const

返回 true if the string is uppercase, that is, it's identical to its toUpper () folding.

Note that this does not mean that the string does not contain lowercase letters (some lowercase letters do not have a uppercase folding; they are left unchanged by toUpper ()). For more information, refer to the Unicode standard, section 3.13.

该函数在 Qt 5.12 引入。

另请参阅 QChar::toUpper () 和 isLower ().

[since 5.15] bool QString:: isValidUtf16 () const

返回 true if the string contains valid UTF-16 encoded data, or false 否则。

Note that this function does not perform any special validation of the data; it merely checks if it can be successfully decoded from UTF-16. The data is assumed to be in host byte order; the presence of a BOM is meaningless.

该函数在 Qt 5.15 引入。

另请参阅 QStringView::isValidUtf16 ().

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

Returns the string that contains the last n 个字符对于此字符串。

注意： 行为未定义当 n < 0 or n > size ().

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

该函数在 Qt 6.0 引入。

另请参阅 first (), sliced (), endsWith (), chopped (), chop ()，和 truncate ().

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 from is -2, at the next to last character and so on. Returns -1 if str 找不到。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1
						

注意： When searching for a 0-length str , the match at the end of the data is excluded from the search by a negative from , even though -1 is normally thought of as searching from the end of the string: the match at the end is after the last character, so it is excluded. To include such a final empty match, either give a positive value for from or omit the from parameter entirely.

另请参阅 indexOf (), contains ()，和 count ().

qsizetype QString:: lastIndexOf ( QChar ch , qsizetype from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the character ch , searching backward from position from .

[since 6.2] qsizetype QString:: lastIndexOf ( QLatin1String 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 (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1
						

该函数在 Qt 6.2 引入。

另请参阅 indexOf (), contains ()，和 count ().

qsizetype QString:: lastIndexOf ( QLatin1String str , qsizetype from , 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, searching backward from index position from 。若 from is -1, the search starts at the last character; if from is -2, at the next to last character and so on. Returns -1 if str 找不到。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1
						

注意： When searching for a 0-length str , the match at the end of the data is excluded from the search by a negative from , even though -1 is normally thought of as searching from the end of the string: the match at the end is after the last character, so it is excluded. To include such a final empty match, either give a positive value for from or omit the from parameter entirely.

另请参阅 indexOf (), contains ()，和 count ().

[since 6.2] qsizetype QString:: lastIndexOf (const QString & str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the string str in this string. Returns -1 if str 找不到。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

QString x = "crazy azimuths";
QString y = "az";
x.lastIndexOf(y);           // returns 6
x.lastIndexOf(y, 6);        // returns 6
x.lastIndexOf(y, 5);        // returns 2
x.lastIndexOf(y, 1);        // returns -1
						

该函数在 Qt 6.2 引入。

另请参阅 indexOf (), contains ()，和 count ().

[since 6.2] qsizetype QString:: lastIndexOf ( QStringView str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

This function overloads lastIndexOf().

Returns the index position of the last occurrence of the string view str in this string. Returns -1 if str 找不到。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

该函数在 Qt 6.2 引入。

另请参阅 indexOf (), contains ()，和 count ().

[since 5.14] 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 from is -2, at the next to last character and so on. Returns -1 if str 找不到。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

注意： When searching for a 0-length str , the match at the end of the data is excluded from the search by a negative from , even though -1 is normally thought of as searching from the end of the string: the match at the end is after the last character, so it is excluded. To include such a final empty match, either give a positive value for from or omit the from parameter entirely.

该函数在 Qt 5.14 引入。

另请参阅 indexOf (), contains ()，和 count ().

[since 6.2] qsizetype QString:: lastIndexOf (const QRegularExpression & re , QRegularExpressionMatch * rmatch = nullptr) const

This function overloads lastIndexOf().

Returns the index position of the last match of the regular expression re in the string. Returns -1 if re didn't match anywhere.

若匹配成功且 rmatch 不是 nullptr ，它还把匹配结果写入 QRegularExpressionMatch 对象指向的 rmatch .

范例：

QString str = "the minimum";
str.lastIndexOf(QRegularExpression("m[aeiou]"));      // returns 8
QString str = "the minimum";
QRegularExpressionMatch match;
str.lastIndexOf(QRegularExpression("m[aeiou]"), -1, &match);      // returns 8
// match.captured() == mu
						

注意： Due to how the regular expression matching algorithm works, this function will actually match repeatedly from the beginning of the string until the end of the string is reached.

该函数在 Qt 6.2 引入。

[since 5.5] 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 from is -2, at the next to last character and so on. Returns -1 if re didn't match anywhere.

若匹配成功且 rmatch 不是 nullptr ，它还把匹配结果写入 QRegularExpressionMatch 对象指向的 rmatch .

范例：

QString str = "the minimum";
str.lastIndexOf(QRegularExpression("m[aeiou]"));      // returns 8
QString str = "the minimum";
QRegularExpressionMatch match;
str.lastIndexOf(QRegularExpression("m[aeiou]"), -1, &match);      // returns 8
// match.captured() == mu
						

注意： Due to how the regular expression matching algorithm works, this function will actually match repeatedly from the beginning of the string until the position from is reached.

注意： When searching for a regular expression re that may match 0 characters, the match at the end of the data is excluded from the search by a negative from , even though -1 is normally thought of as searching from the end of the string: the match at the end is after the last character, so it is excluded. To include such a final empty match, either give a positive value for from or omit the from parameter entirely.

该函数在 Qt 5.5 引入。

QString QString:: left ( qsizetype n ) const

Returns a substring that contains the n leftmost characters of the string.

若知道 n 不可以超出边界，使用 first () 代替在新代码中，因为它更快。

返回整个字符串若 n >= size ()，或小于 0。

另请参阅 first (), last (), startsWith (), chopped (), chop ()，和 truncate ().

QString QString:: leftJustified ( qsizetype width , QChar fill = QLatin1Char(' '), 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"
						

另请参阅 rightJustified ().

qsizetype QString:: length () const

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

另请参阅 resize ().

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

比较 s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

另请参阅 compare (), QLocale ，和 Comparing Strings .

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) .

另请参阅 Comparing Strings .

[since 6.0] int QString:: localeAwareCompare ( QStringView other ) const

This function overloads localeAwareCompare().

Compares this string with the other string and returns an integer less than, equal to, or greater than zero if this string is less than, equal to, or greater than the other 字符串。

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

如同 localeAwareCompare(*this, other) .

该函数在 Qt 6.0 引入。

另请参阅 Comparing Strings .

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

This function overloads localeAwareCompare().

比较 s1 with s2 and returns an integer less than, equal to, or greater than zero if s1 is less than, equal to, or greater than s2 .

The comparison is performed in a locale- and also platform-dependent manner. Use this function to present sorted lists of strings to the user.

该函数在 Qt 6.0 引入。

另请参阅 Comparing Strings .

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

返回字符串包含 n 个字符对于此字符串，起始于指定 position 索引。

若知道 position and n 不可以超出边界，使用 sliced () 代替在新代码中，因为它更快。

返回 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 .

另请参阅 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 根据指定 base .

The base is 10 by default and must be between 2 and 36. For bases other than 10, n is treated as an unsigned integer.

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

long a = 63;
QString s = QString::number(a, 16);             // s == "3f"
QString t = QString::number(a, 16).toUpper();     // t == "3F"
						

另请参阅 setNum ().

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

[static] QString QString:: number ( double n , char format = 'g', int precision = 6)

Returns a string representing the floating-point number n .

Returns a string that represents n , formatted according to the specified format and precision .

For formats with an exponent, the exponent will show its sign and have at least two digits, left-padding the exponent with zero if needed.

另请参阅 setNum (), QLocale::toString (), QLocale::FloatingPointPrecisionOption ，和 Number Formats .

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

范例：

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

另请参阅 append () 和 insert ().

QString &QString:: prepend ( QChar ch )

This function overloads prepend().

前置字符 ch 到此字符串。

[since 5.5] QString &QString:: prepend (const QChar * str , qsizetype len )

This function overloads prepend().

前置 len 字符来自 QChar array str to this string and returns a reference to this string.

该函数在 Qt 5.5 引入。

[since 6.0] QString &QString:: prepend ( QStringView str )

This function overloads prepend().

Prepends the string view str to the beginning of this string and returns a reference to this string.

该函数在 Qt 6.0 引入。

QString &QString:: prepend ( QLatin1String str )

This function overloads prepend().

Prepends the Latin-1 string str 到此字符串。

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 () 函数。

可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

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

This function overloads prepend().

前置字节数组 ba to this string. The byte array is converted to Unicode using the fromUtf8 () 函数。

可以禁用此函数通过定义 QT_NO_CAST_FROM_ASCII when you compile your applications. This can be useful if you want to ensure that all user-visible strings go through QObject::tr (), for example.

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) .

另请参阅 append ().

void QString:: push_back ( QChar ch )

这是重载函数。

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) .

另请参阅 prepend ().

void QString:: push_front ( QChar ch )

这是重载函数。

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

[since 5.6] QString::reverse_iterator QString:: rbegin ()

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

警告： 返回迭代器不验证当分离时或当 QString 被修改。

该函数在 Qt 5.6 引入。

另请参阅 begin (), crbegin ()，和 rend ().

[since 5.6] QString::const_reverse_iterator QString:: rbegin () const

这是重载函数。

该函数在 Qt 5.6 引入。

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 .

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.

另请参阅 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 (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

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

这如同 replace(ch, "", cs) .

Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze () after the last change to the string's size.

另请参阅 replace ().

[since 5.11] QString &QString:: remove ( QLatin1String str , Qt::CaseSensitivity cs = Qt::CaseSensitive)

这是重载函数。

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

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

这如同 replace(str, "", cs) .

Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze () after the last change to the string's size.

该函数在 Qt 5.11 引入。

另请参阅 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 (default), the search is case sensitive; otherwise the search is case insensitive.

这如同 replace(str, "", cs) .

Element removal will preserve the string's capacity and not reduce the amount of allocated memory. To shed extra capacity and free as much memory as possible, call squeeze () after the last change to the string's size.

另请参阅 replace ().

[since 5.0] 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.

该函数在 Qt 5.0 引入。

另请参阅 indexOf (), lastIndexOf ()，和 replace ().

[since 6.1] template <typename Predicate> QString &QString:: removeIf ( Predicate pred )

Removes all elements for which the predicate pred returns true from the string. Returns a reference to the string.

该函数在 Qt 6.1 引入。

另请参阅 remove ().

[since 5.6] QString::reverse_iterator QString:: rend ()

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

警告： 返回迭代器不验证当分离时或当 QString 被修改。

该函数在 Qt 5.6 引入。

另请参阅 end (), crend ()，和 rbegin ().

[since 5.6] QString::const_reverse_iterator QString:: rend () const

这是重载函数。

该函数在 Qt 5.6 引入。

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.

范例：

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

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

替换 n characters beginning at index position 采用字符串 after 并返回此字符串的引用。

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.

范例：

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

另请参阅 insert () 和 remove ().

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

此函数重载 replace()。

替换 n characters beginning at index position with the character after 并返回此字符串的引用。

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

此函数重载 replace()。

替换 n characters beginning at index position with the first size characters of the QChar array unicode 并返回此字符串的引用。

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

此函数重载 replace()。

Replaces every occurrence of the character before with the character after 并返回此字符串的引用。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

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

此函数重载 replace()。

Replaces each occurrence in this string of the first blen 字符的 before with the first alen 字符的 after 并返回此字符串的引用。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace ( QLatin1String before , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函数重载 replace()。

Replaces every occurrence of the string before 采用字符串 after 并返回此字符串的引用。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

注意： The text is not rescanned after a replacement.

QString &QString:: replace ( QLatin1String before , const QString & after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函数重载 replace()。

Replaces every occurrence of the string before 采用字符串 after 并返回此字符串的引用。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

注意： The text is not rescanned after a replacement.

QString &QString:: replace (const QString & before , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函数重载 replace()。

Replaces every occurrence of the string before 采用字符串 after 并返回此字符串的引用。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

注意： The text is not rescanned after a replacement.

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

此函数重载 replace()。

Replaces every occurrence of the string before 采用字符串 after 并返回此字符串的引用。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

范例：

QString str = "colour behaviour flavour neighbour";
str.replace(QString("ou"), QString("o"));
// str == "color behavior flavor neighbor"
						

注意： The replacement text is not rescanned after it is inserted.

范例：

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

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

此函数重载 replace()。

Replaces every occurrence of the character ch in the string with after 并返回此字符串的引用。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

QString &QString:: replace ( QChar c , QLatin1String after , Qt::CaseSensitivity cs = Qt::CaseSensitive)

此函数重载 replace()。

Replaces every occurrence of the character c 采用字符串 after 并返回此字符串的引用。

若 cs is Qt::CaseSensitive (default), the search is case sensitive; otherwise the search is case insensitive.

注意： The text is not rescanned after a replacement.

[since 5.0] QString &QString:: replace (const QRegularExpression & re , const QString & after )

此函数重载 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}."
						

该函数在 Qt 5.0 引入。

另请参阅 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();
						

另请参阅 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 ().

范例：

QString s = "Hello world";
s.resize(5);
// s == "Hello"
s.resize(8);
// s == "Hello???" (where ? stands for any character)
						

If you want to append a certain number of identical characters to the string, use the resize (qsizetype, QChar ) overload.

If you want to expand the string so that it reaches a certain width and fill the new positions with a particular character, use the leftJustified () 函数：

若 size 为负，相当于传递 0。

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

另请参阅 truncate (), reserve ()，和 squeeze ().

[since 5.7] void QString:: resize ( qsizetype size , QChar fillChar )

这是重载函数。

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

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

该函数在 Qt 5.7 引入。

QString QString:: right ( qsizetype n ) const

Returns a substring that contains the n rightmost characters of the string.

若知道 n 不可以超出边界，使用 last () 代替在新代码中，因为它更快。

返回整个字符串若 n >= size ()，或小于 0。

另请参阅 endsWith (), last (), first (), sliced (), chopped (), chop ()，和 truncate ().

QString QString:: rightJustified ( qsizetype width , QChar fill = QLatin1Char(' '), 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"
						

另请参阅 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.

flags argument can be used to affect some aspects of the function's behavior, e.g. whether to be case sensitive, whether to skip empty fields and how to deal with leading and trailing separators; see SectionFlags .

QString str;
QString csv = "forename,middlename,surname,phone";
QString path = "/usr/local/bin/myapp"; // First field is empty
QString::SectionFlag flag = QString::SectionSkipEmpty;
str = csv.section(',', 2, 2);   // str == "surname"
str = path.section('/', 3, 4);  // str == "bin/myapp"
str = path.section('/', 3, 3, flag); // str == "myapp"
						

若 start or end is negative, we count fields from the right of the string, the right-most field being -1, the one from right-most field being -2, and so on.

str = csv.section(',', -3, -2);  // str == "middlename,surname"
str = path.section('/', -1); // str == "myapp"
						

另请参阅 split ().

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"
						

另请参阅 split ().

[since 5.0] 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.

该函数在 Qt 5.0 引入。

另请参阅 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"
						

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

另请参阅 number ().

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

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

这是重载函数。

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

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

另请参阅 number ().

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

这是重载函数。

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

另请参阅 number (), QLocale::FloatingPointPrecisionOption ，和 Number Formats .

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.

另请参阅 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 .

另请参阅 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.

另请参阅 utf16 () 和 setUnicode ().

[since 5.10] void QString:: shrink_to_fit ()

此函数为兼容 STL (标准模板库) 提供。它相当于 squeeze ().

该函数在 Qt 5.10 引入。

另请参阅 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.

空白意味着任何字符其。 QChar::isSpace () 返回 true 。这包括 ASCII 字符 \t、\n、\v、\f、\r、及 " "。

范例：

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

另请参阅 trimmed ().

qsizetype QString:: size () const

Returns the number of characters in this string.

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

范例：

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

另请参阅 isEmpty () 和 resize ().

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

返回字符串包含 n characters of this string, starting at position pos .

注意： 行为未定义当 pos < 0, n < 0, or pos + n > size ().

QString x = "Nine pineapples";
QString y = x.sliced(5, 4);            // y == "pine"
QString z = x.sliced(5);               // z == "pineapples"
						

该函数在 Qt 6.0 引入。

另请参阅 first (), last (), chopped (), chop ()，和 truncate ().

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

这是重载函数。

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

注意： 行为未定义当 pos < 0 or pos > size ().

该函数在 Qt 6.0 引入。

另请参阅 first (), last (), sliced (), chopped (), chop ()，和 truncate ().