QString 类

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
						

All functions except isNull () treat null strings the same as empty strings. For example, toUtf8 (). constData () returns a pointer to a '\0' character for a null string ( not a null pointer), and QString () compares equal to QString (""). We recommend that you always use the isEmpty () function and avoid isNull ().

自变量格式

成员函数中的自变量 format 可以指定 (如： arg (), number ())，自变量 format can be one of the following:

A precision is also specified with the argument format . For the 'e', 'E', and 'f' formats, the precision represents the number of digits after the decimal point. For the 'g' and 'G' formats, the precision represents the maximum number of significant digits (trailing zeroes are omitted).

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->setText(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 () needs an extra test).

There are two ways you can access this improved method of string construction. The straightforward way is to include QStringBuilder wherever you want to use it, and use the '%' operator instead of '+' when concatenating strings:

    #include <QStringBuilder>
    QString hello("hello");
    QStringRef el(&hello, 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.

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

成员类型文档编制

typedef QString:: ConstIterator

Qt 样式同义词 QString::const_iterator .

typedef 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.

The SectionFlags type is a typedef for QFlags <SectionFlag>. It stores an OR combination of SectionFlag values.

另请参阅 section ().

enum QString:: SplitBehavior

This enum specifies how the split () function should behave with respect to empty strings.

另请参阅 split ().

typedef QString:: const_iterator

This typedef provides an STL-style const iterator for QString .

另请参阅 QString::iterator .

typedef QString:: const_pointer

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

typedef QString:: const_reference

This typedef provides an STL-style const reference for a QString 元素 ( QChar ).

typedef QString:: const_reverse_iterator

This typedef provides an STL-style const reverse iterator for QString .

该 typedef 在 Qt 5.6 引入。

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

typedef QString:: difference_type

QString::size_type typedef provides an STL-style type for difference between pointers.

typedef QString:: iterator

The QString::iterator typedef provides an STL-style non-const iterator for QString .

另请参阅 QString::const_iterator .

typedef QString:: pointer

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

typedef QString:: reference

This typedef provides an STL-style reference for a QString 元素 ( QChar ).

typedef QString:: reverse_iterator

This typedef provides an STL-style non-const reverse iterator for QString .

该 typedef 在 Qt 5.6 引入。

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

typedef QString:: size_type

The QString::size_type typedef provides an STL-style type for sizes (int).

typedef QString:: value_type

This typedef provides an STL-style value type for QString .

成员函数文档编制

QString:: QString ()

Constructs a null string. Null strings are also empty.

另请参阅 isEmpty ().

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

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

若 unicode is 0, a null string is constructed.

若 size is negative, unicode is assumed to point to a nul-terminated array and its length is determined dynamically. The terminating nul-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 ( QChar ch )

Constructs a string of size 1 containing the character ch .

QString:: QString ( int size , QChar ch )

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

另请参阅 fill ().

QString:: QString ( QLatin1String str )

Constructs a copy of the Latin-1 string str .

另请参阅 fromLatin1 ().

QString:: QString (const QString & other )

构造副本为 other .

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

另请参阅 operator= ().

QString:: QString ( QString && other )

移动构造 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 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 ().

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 ()

销毁字符串。

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

追加字符串 str onto the end of this string.

范例：

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

这如同使用 insert () 函数：

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

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

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

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

此函数重载 append ().

追加 len characters from the QChar array str 到此字符串。

该函数在 Qt 5.0 引入。

QString &QString:: append ( QChar ch )

此函数重载 append ().

追加字符 ch 到此字符串。

QString &QString:: append (const QStringRef & reference )

追加给定字符串 reference to this string and returns the result.

该函数在 Qt 4.4 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 ( 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.

若 fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

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"
						

若 fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

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.

若 fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

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 "C" 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"
						

若 fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

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.

若 fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

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.

若 fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

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.

若 fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

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

此函数重载 arg ().

Argument a is formatted according to the specified format and precision 。见 自变量格式 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"
						

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 "C" locale is used.

若 fillChar is '0' (the number 0, ASCII 48), this function will use the locale's zero to pad. For negative numbers, the zero padding will probably appear before the minus sign.

另请参阅 QLocale::toString ().

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

此函数重载 arg ().

a argument is interpreted as a Latin-1 character.

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

此函数重载 arg ().

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.

若 fillChar is '0' (the number 0, ASCII 48), the locale's zero is used. For negative numbers, zero padding might appear before the minus sign.

QString QString:: arg (const QString & a1 , const QString & a2 ) const

此函数重载 arg ().

这如同 str.arg(a1).arg(a2) , except that the strings a1 and a2 are replaced in one pass. This can make a difference if a1 contains e.g. %1 :

QString str;
str = "%1 %2";
str.arg("%1f", "Hello");        // returns "%1f Hello"
str.arg("%1f").arg("Hello");    // returns "Hellof %2"
						

A similar problem occurs when the numbered place markers are not white space separated:

QString str;
str = "%1%3%2";
str.arg("Hello").arg(20).arg(50); // returns "Hello500"
str = "%1%2%3";
str.arg("Hello").arg(50).arg(20); // returns "Hello5020"
						

Let's look at the substitutions:

• 首先， Hello 替换 %1 so the string becomes "Hello%3%2" .
• Then, 20 替换 %2 so the string becomes "Hello%320" .
• Since the maximum numbered place marker value is 99, 50 替换 %32 .

Thus the string finally becomes "Hello500" .

In such cases, the following yields the expected results:

QString str;
str = "%1%2%3";
str.arg("Hello", QString::number(20), QString::number(50)); // returns "Hello5020"
						

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 ) const

此函数重载 arg ().

这如同调用 str.arg(a1).arg(a2).arg(a3) , except that the strings a1 , a2 and a3 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 ) const

此函数重载 arg ().

这如同调用 str.arg(a1).arg(a2).arg(a3).arg(a4) , except that the strings a1 , a2 , a3 and a4 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 ) const

此函数重载 arg ().

这如同调用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5) , except that the strings a1 , a2 , a3 , a4 ，和 a5 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 ) const

此函数重载 arg ().

这如同调用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6)) , except that the strings a1 , a2 , a3 , a4 , a5 ，和 a6 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 , const QString & a7 ) const

此函数重载 arg ().

这如同调用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7) , except that the strings a1 , a2 , a3 , a4 , a5 , a6 ，和 a7 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 , const QString & a7 , const QString & a8 ) const

此函数重载 arg ().

这如同调用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7).arg(a8) , except that the strings a1 , a2 , a3 , a4 , a5 , a6 , a7 ，和 a8 are replaced in one pass.

QString QString:: arg (const QString & a1 , const QString & a2 , const QString & a3 , const QString & a4 , const QString & a5 , const QString & a6 , const QString & a7 , const QString & a8 , const QString & a9 ) const

此函数重载 arg ().

这如同调用 str.arg(a1).arg(a2).arg(a3).arg(a4).arg(a5).arg(a6).arg(a7).arg(a8).arg(a9) , except that the strings a1 , a2 , a3 , a4 , a5 , a6 , a7 , a8 ，和 a9 are replaced in one pass.

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

Safely builds a formatted string from the format string cformat and an arbitrary list of arguments.

The format string supports the conversion specifiers, length modifiers, and flags provided by printf() in the standard C++ library. The cformat string and %s arguments must be UTF-8 encoded.

注意： %lc escape sequence expects a unicode character of type char16_t ，或 ushort (as returned by QChar::unicode ())。 %ls escape sequence expects a pointer to a zero-terminated array of unicode characters of type char16_t , or ushort (as returned by QString::utf16 ()). This is at odds with the printf() in the standard C++ library, which defines %lc to print a wchar_t and %ls to print a wchar_t* , and might also produce compiler warnings on platforms where the size of wchar_t is not 16 bits.

警告： We do not recommend using QString::asprintf() in new Qt code. Instead, consider using QTextStream or arg (), both of which support Unicode strings seamlessly and are type-safe. Here's an example that uses QTextStream :

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

For translations , especially if the strings contains more than one escape sequence, you should consider using the arg () function instead. This allows the order of the replacements to be controlled by the translator.

该函数在 Qt 5.5 引入。

另请参阅 arg ().

const QChar QString:: at ( int position ) const

Returns the character at the given index position in the string.

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

另请参阅 operator[] ().

iterator QString:: begin ()

返回 STL 样式迭代器 pointing to the first character in the string.

另请参阅 constBegin () 和 end ().

const_iterator QString:: begin () const

此函数重载 begin ().

int 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 ().

另请参阅 reserve () 和 squeeze ().

const_iterator QString:: cbegin () const

返回常量 STL 样式迭代器 pointing to the first character in the string.

该函数在 Qt 5.0 引入。

另请参阅 begin () 和 cend ().

const_iterator QString:: cend () const

返回常量 STL 样式迭代器 pointing to the imaginary character after the last character in the list.

该函数在 Qt 5.0 引入。

另请参阅 cbegin () 和 end ().

void QString:: chop ( int n )

移除 n characters from the end of the string.

若 n is greater than or equal to size (), the result is an empty string; if n is negative, it is equivalent to passing zero.

范例：

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

If you want to remove characters from the beginning of the string, use remove () 代替。

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

void QString:: clear ()

Clears the contents of the string and makes it 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
						

该函数在 Qt 4.2 引入。

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

int QString:: compare ( QLatin1String other , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 compare ().

Same as compare(*this, other , cs ).

该函数在 Qt 4.2 引入。

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.

Same as compare(*this, other , cs ).

该函数在 Qt 4.2 引入。

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

此函数重载 compare ().

Performs a comparison of s1 and s2 , using the case sensitivity setting cs .

该函数在 Qt 4.2 引入。

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

此函数重载 compare ().

Performs a comparison of s1 and s2 , using the case sensitivity setting cs .

该函数在 Qt 4.2 引入。

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

此函数重载 compare ().

Compares the string reference, ref , with the string and returns an integer less than, equal to, or greater than zero if the string is less than, equal to, or greater than ref .

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

此函数重载 compare ().

const_iterator QString:: constBegin () const

返回常量 STL 样式迭代器 pointing to the first character in the string.

另请参阅 begin () 和 constEnd ().

const QChar *QString:: constData () const

Returns a pointer to the data stored in the QString . The pointer can be used to access the characters that compose the string.

Note that the pointer remains valid only as long as the string is not modified.

注意： The returned string may not be '\0'-terminated. Use size () to determine the length of the array.

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

const_iterator QString:: constEnd () const

返回常量 STL 样式迭代器 pointing to the imaginary character after the last character in the list.

另请参阅 constBegin () 和 end ().

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

返回 true if this string contains an occurrence of the string 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 if this string contains an occurrence of the character ch ；否则返回 false .

bool QString:: contains ( QLatin1String str , Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 contains ().

返回 true if this string contains an occurrence of the latin-1 string str ；否则返回 false .

该函数在 Qt 5.3 引入。

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

返回 true if this string contains an occurrence of the string reference 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 4.8 引入。

另请参阅 indexOf () 和 count ().

bool QString:: contains (const QRegExp & rx ) const

此函数重载 contains ().

返回 true if the regular expression rx matches somewhere in this string; otherwise returns false .

bool QString:: contains ( QRegExp & rx ) const

此函数重载 contains ().

返回 true if the regular expression rx matches somewhere in this string; otherwise returns false .

If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength , QRegExp::cap ).

该函数在 Qt 4.5 引入。

bool QString:: contains (const QRegularExpression & re ) const

此函数重载 contains ().

返回 true if the regular expression re matches somewhere in this string; otherwise returns false .

该函数在 Qt 5.0 引入。

bool QString:: contains (const QRegularExpression & re , QRegularExpressionMatch * match ) const

此函数重载 contains ().

返回 true if the regular expression re matches somewhere in this string; otherwise returns false .

If the match is successful and match is not a null pointer, it also writes the results of the match into the QRegularExpressionMatch object pointed to by match .

该函数在 Qt 5.1 引入。

另请参阅 QRegularExpression::match ().

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

Returns the number of (potentially overlapping) occurrences of the string str in this string.

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

另请参阅 contains () 和 indexOf ().

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

此函数重载 count ().

Returns the number of occurrences of character ch in the string.

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

另请参阅 contains () 和 indexOf ().

int QString:: count () const

This function overloads count().

如同 size ().

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

此函数重载 count ().

Returns the number of (potentially overlapping) occurrences of the string reference str in this string.

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

该函数在 Qt 4.8 引入。

另请参阅 contains () 和 indexOf ().

int QString:: count (const QRegExp & rx ) const

此函数重载 count ().

Returns the number of times the regular expression rx matches in the string.

This function counts overlapping matches, so in the example below, there are four instances of "ana" or "ama":

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

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

此函数重载 count ().

Returns the number of times the regular expression re matches in the string.

This function counts overlapping matches, so in the example below, there are four instances of "ana" or "ama":

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

该函数在 Qt 5.0 引入。

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.

该函数在 Qt 5.6 引入。

另请参阅 begin (), rbegin ()，和 rend ().

const_reverse_iterator QString:: crend () const

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

该函数在 Qt 5.6 引入。

另请参阅 end (), rend ()，和 rbegin ().

QChar *QString:: data ()

Returns a pointer to the data stored in the QString . The pointer can be used to access and modify the characters that compose the string.

不像 constData () 和 unicode (), the returned data is always '\0'-terminated.

范例：

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

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

另请参阅 constData () 和 operator[] ().

const QChar *QString:: data () const

这是重载函数。

注意： The returned string may not be '\0'-terminated. Use size () to determine the length of the array.

另请参阅 fromRawData ().

iterator QString:: end ()

返回 STL 样式迭代器 pointing to the imaginary character after the last character in the string.

另请参阅 begin () 和 constEnd ().

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 if the string ends with 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 ().

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

此函数重载 endsWith ().

返回 true if the string ends with the string reference s ；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 4.8 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 if the string ends with c ；否则返回 false .

此函数重载 endsWith ().

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

Sets every character in the string to character ch 。若 size is different from -1 (default), the string is resized to size beforehand.

范例：

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

另请参阅 resize ().

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

构造新的 QString containing a copy of the string CFString.

注意： this function is only available on OS X and iOS.

该函数在 Qt 5.2 引入。

[static] QString QString:: fromLatin1 (const char * str , int size = -1)

返回 QString initialized with the first size characters of the Latin-1 string str .

若 size is -1 (default), it is taken to be strlen( str ).

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

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

这是重载函数。

返回 QString initialized with the Latin-1 string str .

该函数在 Qt 5.0 引入。

[static] QString QString:: fromLocal8Bit (const char * str , int size = -1)

返回 QString initialized with the first size characters of the 8-bit string str .

若 size is -1 (default), it is taken to be strlen( str ).

QTextCodec::codecForLocale () is used to perform the conversion.

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

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

构造新的 QString containing a copy of the string NSString.

注意： this function is only available on OS X and iOS.

该函数在 Qt 5.2 引入。

[static] QString QString:: fromRawData (const QChar * unicode , int 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's 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};
int size = sizeof(unicode) / sizeof(QChar);
QString str = QString::fromRawData(unicode, size);
if (str.contains(pattern) {
    // ...
}
						

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

另请参阅 fromUtf16 () 和 setRawData ().

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

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

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

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

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

该函数在 Qt 5.5 引入。

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

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

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

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] QString QString:: fromUcs4 (const uint * unicode , int size = -1)

返回 QString initialized with the first size characters of the Unicode string unicode (ISO-10646-UCS-4 encoded).

若 size is -1 (default), unicode must be terminated with a 0.

该函数在 Qt 4.2 引入。

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

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

返回 QString initialized with the first size characters of the Unicode string str (ISO-10646-UCS-4 encoded).

若 size is -1 (default), str must be terminated with a 0.

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 , int size = -1)

返回 QString initialized with the first size bytes of the UTF-8 string str .

若 size is -1 (default), it is taken to be strlen( str ).

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 QTextDecoder .

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

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

返回 QString initialized with the first size characters of the Unicode string unicode (ISO-10646-UTF-16 encoded).

若 size is -1 (default), unicode must be terminated with a 0.

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.

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

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

返回 QString initialized with the first size characters of the Unicode string str (ISO-10646-UTF-16 encoded).

若 size is -1 (default), str must be terminated with a 0.

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 , int 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 has to be 0 terminated.

该函数在 Qt 4.2 引入。

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

int QString:: indexOf (const QString & str , int 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 ().

int QString:: indexOf ( QChar ch , int 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.

int QString:: indexOf ( QLatin1String str , int 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.

该函数在 Qt 4.5 引入。

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

int QString:: indexOf (const QStringRef & str , int 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 reference 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.

该函数在 Qt 4.8 引入。

int QString:: indexOf (const QRegExp & rx , int from = 0) const

此函数重载 indexOf ().

Returns the index position of the first match of the regular expression rx in the string, searching forward from index position from . Returns -1 if rx didn't match anywhere.

范例：

QString str = "the minimum";
str.indexOf(QRegExp("m[aeiou]"), 0);       // returns 4
						

int QString:: indexOf ( QRegExp & rx , int from = 0) const

此函数重载 indexOf ().

Returns the index position of the first match of the regular expression rx in the string, searching forward from index position from . Returns -1 if rx didn't match anywhere.

If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength , QRegExp::cap ).

范例：

QString str = "the minimum";
str.indexOf(QRegExp("m[aeiou]"), 0);       // returns 4
						

该函数在 Qt 4.5 引入。

int QString:: indexOf (const QRegularExpression & re , int from = 0) const

此函数重载 indexOf ().

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.

范例：

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

该函数在 Qt 5.0 引入。

int QString:: indexOf (const QRegularExpression & re , int from , QRegularExpressionMatch * rmatch ) const

这是重载函数。

Returns the index position of the first match of the regular expression re in the string, searching forward from index position from . Returns -1 if re didn't match anywhere.

If the match is successful and rmatch is not a null pointer, it also writes the results of the match into the QRegularExpressionMatch object pointed to by rmatch .

范例：

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 ( int position , const QString & str )

Inserts the string str at the given index position and returns a reference to this string.

范例：

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

若给定 position 大于 size (), the array is first extended using resize ().

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

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

此函数重载 insert ().

Inserts the first size characters of the QChar array unicode at the given index position in the string.

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

此函数重载 insert ().

插入 ch at the given index position in the string.

QString &QString:: insert ( int position , const QStringRef & str )

此函数重载 insert ().

Inserts the string reference str at the given index position and returns a reference to this string.

若给定 position 大于 size (), the array is first extended using resize ().

该函数在 Qt 5.5 引入。

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

此函数重载 insert ().

Inserts the Latin-1 string str at the given index position .

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

此函数重载 insert ().

Inserts the C string str at the given index position and returns a reference to this string.

若给定 position 大于 size (), the array is first extended using resize ().

This function is not available when QT_NO_CAST_FROM_ASCII is defined.

该函数在 Qt 5.5 引入。

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

此函数重载 insert ().

Inserts the byte array str at the given index position and returns a reference to this string.

若给定 position 大于 size (), the array is first extended using resize ().

This function is not available when QT_NO_CAST_FROM_ASCII is defined.

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 ().

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 QStringRef::isRightToLeft ().

int QString:: lastIndexOf (const QString & str , int from = -1, 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 (default), 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
						

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

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

此函数重载 lastIndexOf ().

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

int QString:: lastIndexOf ( QLatin1String str , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 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 (default), 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
						

该函数在 Qt 4.5 引入。

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

int QString:: lastIndexOf (const QStringRef & str , int from = -1, Qt::CaseSensitivity cs = Qt::CaseSensitive) const

此函数重载 lastIndexOf ().

Returns the index position of the last occurrence of the string reference str in this string, searching backward from index position from 。若 from is -1 (default), 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.

该函数在 Qt 4.8 引入。

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

int QString:: lastIndexOf (const QRegExp & rx , int from = -1) const

此函数重载 lastIndexOf ().

Returns the index position of the last match of the regular expression rx in the string, searching backward from index position from . Returns -1 if rx didn't match anywhere.

范例：

QString str = "the minimum";
str.lastIndexOf(QRegExp("m[aeiou]"));      // returns 8
						

int QString:: lastIndexOf ( QRegExp & rx , int from = -1) const

此函数重载 lastIndexOf ().

Returns the index position of the last match of the regular expression rx in the string, searching backward from index position from . Returns -1 if rx didn't match anywhere.

If there is a match, the rx regular expression will contain the matched captures (see QRegExp::matchedLength , QRegExp::cap ).

范例：

QString str = "the minimum";
str.lastIndexOf(QRegExp("m[aeiou]"));      // returns 8
						

该函数在 Qt 4.5 引入。

int QString:: lastIndexOf (const QRegularExpression & re , int from = -1) const

此函数重载 lastIndexOf ().

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

范例：

QString str = "the minimum";
str.lastIndexOf(QRegularExpression("m[aeiou]"));      // returns 8
						

该函数在 Qt 5.0 引入。

int QString:: lastIndexOf (const QRegularExpression & re , int from , QRegularExpressionMatch * rmatch ) const

这是重载函数。

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

If the match is successful and rmatch is not a null pointer, it also writes the results of the match into the QRegularExpressionMatch object pointed to by rmatch .

范例：

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

该函数在 Qt 5.5 引入。

QString QString:: left ( int n ) const

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

The entire string is returned if n is greater than or equal to size (), or less than zero.

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

另请参阅 right (), mid ()，和 startsWith ().

QString QString:: leftJustified ( int 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 ().

QStringRef QString:: leftRef ( int n ) const

Returns a substring reference to the n leftmost characters of the string.

若 n is greater than or equal to size (), or less than zero, a reference to the entire string is returned.

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

该函数在 Qt 4.4 引入。

另请参阅 left (), rightRef (), midRef ()，和 startsWith ().

int 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.

On macOS and iOS this function compares according the "Order for sorted lists" setting in the International preferences panel.

另请参阅 compare () 和 QLocale .

int QString:: localeAwareCompare (const QString & other ) const

此函数重载 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) .

int QString:: localeAwareCompare (const QStringRef & other ) const

此函数重载 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 4.5 引入。

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

此函数重载 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 4.5 引入。

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

Returns a string that contains n characters of this string, starting at the specified position index.

Returns a null string if the position index exceeds the length of the string. If there are less than n characters available in the string starting at the given position ，或者若 n is -1 (default), the function returns all characters that are available from the specified position .

范例：

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

另请参阅 left () 和 right ().

QStringRef QString:: midRef ( int position , int n = -1) const

Returns a substring reference to n characters of this string, starting at the specified position .

若 position exceeds the length of the string, a null reference is returned.

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 from the specified position onwards.

范例：

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

该函数在 Qt 4.4 引入。

另请参阅 mid (), leftRef ()，和 rightRef ().

QString QString:: normalized ( 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 ( uint n , int base = 10)

这是重载函数。

[static] QString QString:: number ( int 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 equivalent of the number n , formatted according to the specified format and precision 。见 自变量格式 了解细节。

不像 QLocale::toString (), this function does not honor the user's locale settings.

另请参阅 setNum () 和 QLocale::toString ().

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.

范例：

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

另请参阅 append () 和 insert ().

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

此函数重载 prepend ().

前置 len characters from the QChar array str to this string and returns a reference to this string.

该函数在 Qt 5.5 引入。

QString &QString:: prepend ( QChar ch )

此函数重载 prepend ().

前置字符 ch 到此字符串。

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

此函数重载 prepend ().

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

该函数在 Qt 5.5 引入。

QString &QString:: prepend ( QLatin1String str )

此函数重载 prepend ().

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

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

此函数重载 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 )

此函数重载 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.

reverse_iterator QString:: rbegin ()

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

该函数在 Qt 5.6 引入。

另请参阅 begin (), crbegin ()，和 rend ().

const_reverse_iterator QString:: rbegin () const

这是重载函数。

该函数在 Qt 5.6 引入。

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

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

If the specified position index is within the string, but position + n is beyond the end of the string, the string is truncated at the specified position .

QString s = "Montreal";
s.remove(1, 4);
// s == "Meal"
						

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) .

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) .

另请参阅 replace ().

QString &QString:: remove (const QRegExp & rx )

Removes every occurrence of the regular expression rx in the string, and returns a reference to the string. For example:

QString r = "Telephone";
r.remove(QRegExp("[aeiou]."));
// r == "The"
						

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

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

Removes every occurrence of the regular expression re in the string, and returns a reference to the string. For example:

QString r = "Telephone";
r.remove(QRegularExpression("[aeiou]."));
// r == "The"
						

该函数在 Qt 5.0 引入。

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

reverse_iterator QString:: rend ()

返回 STL-style reverse iterator pointing to one past the last character in the string, in reverse order.

该函数在 Qt 5.6 引入。

另请参阅 end (), crend ()，和 rbegin ().

const_reverse_iterator QString:: rend () const

这是重载函数。

该函数在 Qt 5.6 引入。

QString QString:: repeated ( int 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"
						

该函数在 Qt 4.5 引入。

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

替换 n characters beginning at index position with the string after and returns a reference to this string.

注意： If the specified position index is within the string, but position + n goes outside the strings range, then n will be adjusted to stop at the end of the string.

范例：

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

另请参阅 insert () 和 remove ().

QString &QString:: replace ( int position , int n , const QChar * unicode , int 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 and returns a reference to this string.

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

此函数重载 replace ().

替换 n characters beginning at index position with the character after and returns a reference to this string.

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 and returns a reference to this string.

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

QString &QString:: replace (const QChar * before , int blen , const QChar * after , int 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 and returns a reference to this string.

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

该函数在 Qt 4.5 引入。

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 with the string after and returns a reference to this string.

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.

该函数在 Qt 4.5 引入。

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 with the string after and returns a reference to this string.

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.

该函数在 Qt 4.5 引入。

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 with the string after and returns a reference to this string.

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.

该函数在 Qt 4.5 引入。

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 with the string after 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 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 and returns a reference to this string.

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 with the string after and returns a reference to this string.

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.

该函数在 Qt 4.5 引入。

QString &QString:: replace (const QRegExp & rx , const QString & after )

此函数重载 replace ().

Replaces every occurrence of the regular expression rx in the string with after . Returns a reference to the string. For example:

QString s = "Banana";
s.replace(QRegExp("a[mn]"), "ox");
// s == "Boxoxa"
						

For regular expressions containing capturing parentheses , occurrences of \1 , \2 , ..., in after are replaced with rx .cap(1), cap(2), ...

QString t = "A <i>bon mot</i>.";
t.replace(QRegExp("<i>([^<]*)</i>"), "\\emph{\\1}");
// t == "A \\emph{bon mot}."
						

另请参阅 indexOf (), lastIndexOf (), remove ()，和 QRegExp::cap ().

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 ( int size )

试图分配内存为至少 size characters. If you know in advance how large the string will be, you can call this function, and if you resize the string often you are likely to get better performance. If size is an underestimate, the worst that will happen is that the QString will be a bit slower.

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 change the size of the string, call 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;
int maxSize;
bool condition;
QChar nextChar;
result.reserve(maxSize);
while (condition)
    result.append(nextChar);
result.squeeze();
						

另请参阅 squeeze () 和 capacity ().

void QString:: resize ( int 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 are removed from the end.

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 (int, QChar ) overload.

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

若 size is negative, it is equivalent to passing zero.

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

另请参阅 truncate () 和 reserve ().

void QString:: resize ( int size , QChar fillChar )

这是重载函数。

不像 resize (int), 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 ( int n ) const

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

The entire string is returned if n is greater than or equal to size (), or less than zero.

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

另请参阅 left (), mid ()，和 endsWith ().

QString QString:: rightJustified ( int width , QChar fill = QLatin1Char( ' ' ), bool truncate = false) const

Returns a string of size () width that contains the 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 ().

QStringRef QString:: rightRef ( int n ) const

Returns a substring reference to the n rightmost characters of the string.

若 n is greater than or equal to size (), or less than zero, a reference to the entire string is returned.

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

该函数在 Qt 4.4 引入。

另请参阅 right (), leftRef (), midRef ()，和 endsWith ().

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

此函数重载 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 ().

QString QString:: section (const QRegExp & reg , int start , int end = -1, SectionFlags flags = SectionDefault) const

此函数重载 section ().

This string is treated as a sequence of fields separated by the regular expression, reg .

QString line = "forename\tmiddlename  surname \t \t phone";
QRegExp sep("\\s+");
str = line.section(sep, 2, 2); // str == "surname"
str = line.section(sep, -3, -2); // str == "middlename  surname"
						

警告： Using this QRegExp version is much more expensive than the overloaded string and character versions.

另请参阅 split () 和 simplified ().

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

此函数重载 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. For bases other than 10, n is treated as an unsigned integer.

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.

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

这是重载函数。

QString &QString:: setNum ( short 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.

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.

format can be 'e', 'E', 'f', 'g' or 'G' (see 自变量格式 for an explanation of the formats).

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.

QString &QString:: setRawData (const QChar * unicode , int 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.

该函数在 Qt 4.7 引入。

另请参阅 fromRawData ().

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

Resizes the string to size characters and copies unicode into the string.

若 unicode is 0, nothing is copied, but the string is still resized to size .

另请参阅 unicode () 和 setUtf16 ().

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

Resizes the string to size characters and copies unicode into the string.

若 unicode is 0, 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 ().

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.

Whitespace means any character for which QChar::isSpace () 返回 true . This includes the ASCII characters '\t', '\n', '\v', '\f', '\r', and ' '.

范例：

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

另请参阅 trimmed ().

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