QAnyStringView 类

QAnyStringView 类提供 Latin-1、UTF-8 或 UTF-16 的统一字符串视图，采用只读子集的 QString API. 更多...

头：	#include <QAnyStringView>
CMake:	find_package(Qt6 REQUIRED COMPONENTS Core) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake:	QT += core
Since:	Qt 6.0

注意： 此类的所有函数可重入 .

公共类型

	difference_type
	size_type

公共函数

	QAnyStringView ()
	QAnyStringView (std::nullptr_t)
	QAnyStringView (const Char * str , qsizetype len )
	QAnyStringView (const Char * first , const Char * last )
	QAnyStringView (const Char (&)[N] string = N)
	QAnyStringView (const Char * str )
	QAnyStringView (const QByteArray & str )
	QAnyStringView (const QString & str )
	QAnyStringView (const Container & str )
QChar	back () const
void	chop (qsizetype n )
QAnyStringView	chopped (qsizetype n ) const
const void *	data () const
bool	empty () const
QAnyStringView	first (qsizetype n ) const
QChar	front () const
bool	isEmpty () const
bool	isNull () const
QAnyStringView	last (qsizetype n ) const
qsizetype	length () const
qsizetype	size () const
qsizetype	size_bytes () const
QAnyStringView	sliced (qsizetype pos ) const
QAnyStringView	sliced (qsizetype pos , qsizetype n ) const
QString	toString () const
void	truncate (qsizetype n )
decltype(auto)	visit (Visitor && v ) const

静态公共成员

int	compare (QAnyStringView lhs , QAnyStringView rhs , Qt::CaseSensitivity cs = Qt::CaseSensitive)

bool	operator!= (QAnyStringView lhs , QAnyStringView rhs )
bool	operator< (QAnyStringView lhs , QAnyStringView rhs )
bool	operator<= (QAnyStringView lhs , QAnyStringView rhs )
bool	operator== (QAnyStringView lhs , QAnyStringView rhs )
bool	operator> (QAnyStringView lhs , QAnyStringView rhs )
bool	operator>= (QAnyStringView lhs , QAnyStringView rhs )

详细描述

A QAnyStringView references a contiguous portion of a string it does not own. It acts as an interface type to all kinds of strings, without the need to construct a QString 首先。

不像 QStringView and QUtf8StringView , QAnyStringView can hold strings of any of the following encodings: UTF-8, UTF-16, and Latin-1. The latter is supported because Latin-1, unlike UTF-8, can be efficiently compared to UTF-16 data: a length mismatch already means the strings cannot be equal. This is not true for UTF-8/UTF-16 comparisons, because UTF-8 is a variable-length encoding.

The string may be represented as an array (or an array-compatible data-structure such as QString , std::basic_string, etc.) of char , char8_t , QChar , ushort , char16_t or (on platforms, such as Windows, where it is a 16-bit type) wchar_t .

QAnyStringView is designed as an interface type; its main use-case is as a function parameter type. When QAnyStringViews are used as automatic variables or data members, care must be taken to ensure that the referenced string data (for example, owned by a QString ) outlives the QAnyStringView on all code paths, lest the string view ends up referencing deleted data.

When used as an interface type, QAnyStringView allows a single function to accept a wide variety of string data sources. One function accepting QAnyStringView thus replaces five function overloads (taking QString , (const QChar*, qsizetype) , QUtf8StringView , QLatin1StringView (but see above), and QChar ), while at the same time enabling even more string data sources to be passed to the function, such as u8"Hello World" ， char8_t 字符串文字。

Like elsewhere in Qt, QAnyStringView assumes char data is encoded in UTF-8, unless it is presented as a QLatin1StringView .

Since Qt 6.4, however, UTF-8 string literals that are pure US-ASCII are automatically stored as Latin-1. This is a compile-time check with no runtime overhead. The feature requires compiling in C++20, or with a recent GCC.

QAnyStringViews should be passed by value, not by reference-to-const:

    void myfun1(QAnyStringView sv);        // preferred
    void myfun2(const QAnyStringView &sv); // compiles and works, but slower

QAnyStringView can also be used as the return value of a function, but this is not recommended. QUtf8StringView or QStringView are better suited as function return values. If you call a function returning QAnyStringView, take extra care to not keep the QAnyStringView around longer than the function promises to keep the referenced string data alive. If in doubt, obtain a strong reference to the data by calling toString () to convert the QAnyStringView into a QString .

QAnyStringView 为 文字类型 .

兼容字符类型

QAnyStringView 接受各种字符类型的字符串：

char (有符号和无符号两者)
char8_t (仅 C++20)
char16_t
wchar_t (在此是 16 位类型，如 Windows)
ushort
QChar

The 8-bit character types are interpreted as UTF-8 data (except when presented as a QLatin1StringView ) while the 16-bit character types are interpreted as UTF-16 data in host byte order (the same as QString ).

大小和子字符串

All sizes and positions in QAnyStringView functions are in the encoding's code units (that is, UTF-16 surrogate pairs count as two for the purposes of these functions, the same as in QString , and UTF-8 multibyte sequences count as two, three or four, depending on their length).

另请参阅 QUtf8StringView and QStringView .

成员类型文档编制

QAnyStringView:: difference_type

别名化的 std::ptrdiff_t 。为兼容 STL (标准模板库) 提供。

QAnyStringView:: size_type

别名化的 qsizetype。为兼容 STL (标准模板库) 提供。

成员函数文档编制

`[constexpr]` QAnyStringView:: QAnyStringView ()

构造 null 字符串视图。

另请参阅 isNull ().

`[constexpr]` QAnyStringView:: QAnyStringView ( std::nullptr_t )

构造 null 字符串视图。

另请参阅 isNull ().

`[constexpr]` template <typename Char, if_compatible_char<Char>> QAnyStringView:: QAnyStringView (const Char * str , qsizetype len )

构造字符串视图对 str 按长度 len .

范围 [str,len) must remain valid for the lifetime of this string view object.

传递 nullptr as str 是安全的若 len is 0, too, and results in a null string view.

行为未定义若 len is negative or, when positive, if str is nullptr .

This constructor only participates in overload resolution if Char is a compatible character type.

另请参阅 isNull () 和兼容字符类型 .

`[constexpr]` template <typename Char, if_compatible_char<Char>> QAnyStringView:: QAnyStringView (const Char * first , const Char * last )

构造字符串视图对 first 按长度 ( last - first ).

范围 [first,last) must remain valid for the lifetime of this string view object.

传递 nullptr as first 是安全的若 last is nullptr , too, and results in a null string view.

行为未定义若 last precedes first ，或 first is nullptr and last is not.

This constructor only participates in overload resolution if Char is a compatible character type.

另请参阅 isNull () 和兼容字符类型 .

`[constexpr]` template <typename Char, size_t N> QAnyStringView:: QAnyStringView (const Char (&)[ N ] string = N)

Constructs a string view on the character string literal string . The view covers the array until the first Char(0) is encountered, or N , whichever comes first. If you need the full array, use fromArray() instead.

string must remain valid for the lifetime of this string view object.

This constructor only participates in overload resolution if string is an actual array and Char is a compatible character type.

另请参阅 兼容字符类型 .

`[constexpr]` template <typename Char> QAnyStringView:: QAnyStringView (const Char * str )

构造字符串视图对 str . The length is determined by scanning for the first Char(0) .

str must remain valid for the lifetime of this string view object.

传递 nullptr as str 是安全的且结果在 null 字符串视图中。

This constructor only participates in overload resolution if str is not an array and if Char is a compatible character type.

另请参阅 isNull () 和兼容字符类型 .

QAnyStringView:: QAnyStringView (const QByteArray & str )

构造字符串视图对 str . The data in str is interpreted as UTF-8.

str.data() must remain valid for the lifetime of this string view object.

字符串视图将为 null 当且仅当 str.isNull() .

QAnyStringView:: QAnyStringView (const QString & str )

构造字符串视图对 str .

str.data() must remain valid for the lifetime of this string view object.

字符串视图将为 null 当且仅当 str.isNull() .

`[constexpr]` template <typename Container, if_compatible_container<Container>> QAnyStringView:: QAnyStringView (const Container & str )

构造字符串视图对 str 。长度取自 std::size(str) .

std::data(str) must remain valid for the lifetime of this string view object.

This constructor only participates in overload resolution if 容器 is a container with a compatible character type as value_type .

The string view will be empty if and only if std::size(str) == 0 . It is unspecified whether this constructor can result in a null string view ( std::data(str) would have to return nullptr for this).

另请参阅 isNull () 和 isEmpty ().

`[constexpr]` QChar QAnyStringView:: back () const

返回字符串视图中的最后一个字符。

此函数为兼容 STL (标准模板库) 提供。

警告： 在空字符串视图调用此函数，将构成未定义行为。

另请参阅 front () 和大小和子字符串 .

`[constexpr, since 6.5]` void QAnyStringView:: chop ( qsizetype n )

截取此字符串视图按 n 代码点。

如同 *this = first(size() - n) .

注意： 行为未定义当 n < 0 or n > size ().

该函数在 Qt 6.5 引入。

另请参阅 sliced (), first (), last (), chopped (), truncate ()，和大小和子字符串 .

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: chopped ( qsizetype n ) const

返回子字符串长度 size () - n 起始于此对象的开头。

如同 first(size() - n) .

注意： 行为未定义当 n < 0 or n > size ().

该函数在 Qt 6.5 引入。

另请参阅 sliced (), first (), last (), chop (), truncate ()，和大小和子字符串 .

`[static]` int QAnyStringView:: compare ( QAnyStringView lhs , QAnyStringView rhs , Qt::CaseSensitivity cs = Qt::CaseSensitive)

Returns an integer that compares to zero as lhs compares to rhs .

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

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

`[constexpr]` const void *QAnyStringView:: data () const

Returns a const pointer to the first character in the string view.

注意： The character array represented by the return value is not null-terminated.

另请参阅 size_bytes ().

`[constexpr]` bool QAnyStringView:: empty () const

Returns whether this string view is empty - that is, whether size() == 0 .

此函数为兼容 STL (标准模板库) 提供。

另请参阅 isEmpty (), isNull ()，和 size ().

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: first ( qsizetype n ) const

Returns a string view that contains the first n code points of this string view.

注意： 行为未定义当 n < 0 or n > size ().

该函数在 Qt 6.5 引入。

另请参阅 last (), sliced (), chopped (), chop (), truncate ()，和大小和子字符串 .

`[constexpr]` QChar QAnyStringView:: front () const

Returns the first character in the string view.

此函数为兼容 STL (标准模板库) 提供。

警告： 在空字符串视图调用此函数，将构成未定义行为。

另请参阅 back () 和大小和子字符串 .

`[constexpr]` bool QAnyStringView:: isEmpty () const

Returns whether this string view is empty - that is, whether size() == 0 .

This function is provided for compatibility with other Qt containers.

另请参阅 empty (), isNull ()，和 size ().

`[constexpr]` bool QAnyStringView:: isNull () const

Returns whether this string view is null - that is, whether data() == nullptr .

This functions is provided for compatibility with other Qt containers.

另请参阅 empty (), isEmpty ()，和 size ().

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: last ( qsizetype n ) const

Returns a string view that contains the last n code points of this string view.

注意： 行为未定义当 n < 0 or n > size ().

该函数在 Qt 6.5 引入。

另请参阅 first (), sliced (), chopped (), chop (), truncate ()，和大小和子字符串 .

`[constexpr]` qsizetype QAnyStringView:: length () const

如同 size ().

This function is provided for compatibility with other Qt containers.

另请参阅 size ().

`[constexpr]` qsizetype QAnyStringView:: size () const

Returns the size of this string view, in the encoding's code points.

另请参阅 empty (), isEmpty (), isNull (), size_bytes ()，和大小和子字符串 .

`[constexpr]` qsizetype QAnyStringView:: size_bytes () const

Returns the size of this string view, but in bytes, not code-points.

You can use this function together with data () for hashing or serialization.

此函数为兼容 STL (标准模板库) 提供。

另请参阅 size () 和 data ().

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: sliced ( qsizetype pos ) const

Returns a string view starting at position pos in this object, and extending to its end.

注意： 行为未定义当 pos < 0 or pos > size ().

该函数在 Qt 6.5 引入。

另请参阅 first (), last (), chopped (), chop (), truncate ()，和大小和子字符串 .

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: sliced ( qsizetype pos , qsizetype n ) const

Returns a string view containing n code points of this string view, starting at position pos .

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

该函数在 Qt 6.5 引入。

另请参阅 first (), last (), chopped (), chop (), truncate ()，和大小和子字符串 .

QString QAnyStringView:: toString () const

Returns a deep copy of this string view's data as a QString .

The return value will be a null QString if and only if this string view is null.

`[constexpr, since 6.5]` void QAnyStringView:: truncate ( qsizetype n )

Truncates this string view to n 代码点。

如同 *this = first(n) .

注意： 行为未定义当 n < 0 or n > size ().

该函数在 Qt 6.5 引入。

另请参阅 sliced (), first (), last (), chopped (), chop ()，和大小和子字符串 .

`[constexpr]` template <typename Visitor> decltype ( auto ) QAnyStringView:: visit ( Visitor && v ) const

调用 v with either a QUtf8StringView , QLatin1String ，或 QStringView , depending on the encoding of the string data this string-view references.

This is how most functions taking QAnyStringView fork off into per-encoding functions:

void processImpl(QLatin1String s) { ~~~ }
void processImpl(QUtf8StringView s) { ~~~ }
void processImpl(QStringView s) { ~~~ }
void process(QAnyStringView s)
{
    s.visit([](auto s) { processImpl(s); });
}

Here, we're reusing the same name, s , for both the QAnyStringView object, as well as the lambda's parameter. This is idiomatic code and helps track the identity of the objects through visit() calls, for example in more complex situations such as

bool equal(QAnyStringView lhs, QAnyStringView rhs)
{
    // assuming operator==(QAnyStringView, QAnyStringView) didn't, yet, exist:
    return lhs.visit([rhs](auto lhs) {
        rhs.visit([lhs](auto rhs) {
            return lhs == rhs;
        });
    });
}

visit() requires that all lambda instantiations have the same return type. If they differ, you get a compile error, even if there is a common type. To fix, you can use explicit return types on the lambda, or cast in the return statements:

// wrong:
QAnyStringView firstHalf(QAnyStringView input)
{
    return input.visit([](auto input) {   // ERROR: lambdas return different types
        return input.sliced(0, input.size() / 2);
    });
}
// correct:
QAnyStringView firstHalf(QAnyStringView input)
{
    return input.visit([](auto input) -> QAnyStringView { // OK, explicit return type
        return input.sliced(0, input.size() / 2);
    });
}
// also correct:
QAnyStringView firstHalf(QAnyStringView input)
{
    return input.visit([](auto input) {
        return QAnyStringView(input.sliced(0, input.size() / 2)); // OK, cast to common type
    });
}

QAnyStringView 类

公共类型

公共函数

静态公共成员

相关非成员

详细描述

兼容字符类型

大小和子字符串

成员类型文档编制

QAnyStringView:: difference_type

QAnyStringView:: size_type

成员函数文档编制

[constexpr] QAnyStringView:: QAnyStringView ()

[constexpr] QAnyStringView:: QAnyStringView ( std::nullptr_t )

[constexpr] template <typename Char, if_compatible_char<Char>> QAnyStringView:: QAnyStringView (const Char * str , qsizetype len )

[constexpr] template <typename Char, if_compatible_char<Char>> QAnyStringView:: QAnyStringView (const Char * first , const Char * last )

[constexpr] template <typename Char, size_t N> QAnyStringView:: QAnyStringView (const Char (&)[ N ] string = N)

[constexpr] template <typename Char> QAnyStringView:: QAnyStringView (const Char * str )

QAnyStringView:: QAnyStringView (const QByteArray & str )

QAnyStringView:: QAnyStringView (const QString & str )

[constexpr] template <typename Container, if_compatible_container<Container>> QAnyStringView:: QAnyStringView (const Container & str )

[constexpr] QChar QAnyStringView:: back () const

[constexpr, since 6.5] void QAnyStringView:: chop ( qsizetype n )

[constexpr, since 6.5] QAnyStringView QAnyStringView:: chopped ( qsizetype n ) const

[static] int QAnyStringView:: compare ( QAnyStringView lhs , QAnyStringView rhs , Qt::CaseSensitivity cs = Qt::CaseSensitive)

[constexpr] const void *QAnyStringView:: data () const

[constexpr] bool QAnyStringView:: empty () const

[constexpr, since 6.5] QAnyStringView QAnyStringView:: first ( qsizetype n ) const

[constexpr] QChar QAnyStringView:: front () const

[constexpr] bool QAnyStringView:: isEmpty () const

[constexpr] bool QAnyStringView:: isNull () const

[constexpr, since 6.5] QAnyStringView QAnyStringView:: last ( qsizetype n ) const

[constexpr] qsizetype QAnyStringView:: length () const

[constexpr] qsizetype QAnyStringView:: size () const

[constexpr] qsizetype QAnyStringView:: size_bytes () const

[constexpr, since 6.5] QAnyStringView QAnyStringView:: sliced ( qsizetype pos ) const

[constexpr, since 6.5] QAnyStringView QAnyStringView:: sliced ( qsizetype pos , qsizetype n ) const

QString QAnyStringView:: toString () const

[constexpr, since 6.5] void QAnyStringView:: truncate ( qsizetype n )

[constexpr] template <typename Visitor> decltype ( auto ) QAnyStringView:: visit ( Visitor && v ) const

相关非成员

bool operator!= ( QAnyStringView lhs , QAnyStringView rhs )

bool operator< ( QAnyStringView lhs , QAnyStringView rhs )

bool operator<= ( QAnyStringView lhs , QAnyStringView rhs )

bool operator== ( QAnyStringView lhs , QAnyStringView rhs )

bool operator> ( QAnyStringView lhs , QAnyStringView rhs )

bool operator>= ( QAnyStringView lhs , QAnyStringView rhs )

内容

`[constexpr]` QAnyStringView:: QAnyStringView ()

`[constexpr]` QAnyStringView:: QAnyStringView ( std::nullptr_t )

`[constexpr]` template <typename Char, if_compatible_char<Char>> QAnyStringView:: QAnyStringView (const Char * str , qsizetype len )

`[constexpr]` template <typename Char, if_compatible_char<Char>> QAnyStringView:: QAnyStringView (const Char * first , const Char * last )

`[constexpr]` template <typename Char, size_t N> QAnyStringView:: QAnyStringView (const Char (&)[ N ] string = N)

`[constexpr]` template <typename Char> QAnyStringView:: QAnyStringView (const Char * str )

`[constexpr]` template <typename Container, if_compatible_container<Container>> QAnyStringView:: QAnyStringView (const Container & str )

`[constexpr]` QChar QAnyStringView:: back () const

`[constexpr, since 6.5]` void QAnyStringView:: chop ( qsizetype n )

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: chopped ( qsizetype n ) const

`[static]` int QAnyStringView:: compare ( QAnyStringView lhs , QAnyStringView rhs , Qt::CaseSensitivity cs = Qt::CaseSensitive)

`[constexpr]` const void *QAnyStringView:: data () const

`[constexpr]` bool QAnyStringView:: empty () const

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: first ( qsizetype n ) const

`[constexpr]` QChar QAnyStringView:: front () const

`[constexpr]` bool QAnyStringView:: isEmpty () const

`[constexpr]` bool QAnyStringView:: isNull () const

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: last ( qsizetype n ) const

`[constexpr]` qsizetype QAnyStringView:: length () const

`[constexpr]` qsizetype QAnyStringView:: size () const

`[constexpr]` qsizetype QAnyStringView:: size_bytes () const

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: sliced ( qsizetype pos ) const

`[constexpr, since 6.5]` QAnyStringView QAnyStringView:: sliced ( qsizetype pos , qsizetype n ) const

`[constexpr, since 6.5]` void QAnyStringView:: truncate ( qsizetype n )

`[constexpr]` template <typename Visitor> decltype ( auto ) QAnyStringView:: visit ( Visitor && v ) const