QAnyStringView Class

The QAnyStringView class provides a unified view on Latin-1, UTF-8, or UTF-16 strings with a read-only subset of the QString API. 更多...

頭：	#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： 此類的所有函數可重入 .

公共類型

	difference_type
	size_type

公共函數

	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

靜態公共成員

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 )

詳細描述

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 is a 文字類型 .

Compatible Character Types

QAnyStringView accepts strings over a variety of character types:

char (both signed and unsigned)
char8_t (C++20 only)
char16_t
wchar_t (where it's a 16-bit type, e.g. 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 ).

Sizes and Sub-Strings

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).

另請參閱 QUtf8StringView and QStringView .

成員類型文檔編製

QAnyStringView:: difference_type

彆名化的 std::ptrdiff_t 。為兼容 STL (標準模闆庫) 提供。

QAnyStringView:: size_type

彆名化的 qsizetype。為兼容 STL (標準模闆庫) 提供。

成員函數文檔編製

`[constexpr]` QAnyStringView:: QAnyStringView ()

構造 null 字符串視圖。

另請參閱 isNull ().

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

構造 null 字符串視圖。

另請參閱 isNull ().

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

構造字符串視圖對 str 按長度 len .

範圍 [str,len) 必須在此字符串視圖對象的壽命內保持有效。

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

行為未定義若 len is negative or, when positive, if str is nullptr .

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

另請參閱 isNull () 和 Compatible Character Types .

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

構造字符串視圖對 first 按長度 ( last - first ).

範圍 [first,last) 必須在此字符串視圖對象的壽命內保持有效。

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

行為未定義若 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.

另請參閱 isNull () 和 Compatible Character Types .

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

構造字符串視圖按字符串文字 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 必須在此字符串視圖對象的壽命內保持有效。

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

另請參閱 Compatible Character Types .

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

構造字符串視圖對 str . The length is determined by scanning for the first Char(0) .

str 必須在此字符串視圖對象的壽命內保持有效。

傳遞 nullptr as str 是安全的且結果在 null 字符串視圖中。

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

另請參閱 isNull () 和 Compatible Character Types .

QAnyStringView:: QAnyStringView (const QByteArray & str )

構造字符串視圖對 str . The data in str is interpreted as UTF-8.

str.data() 必須在此字符串視圖對象的壽命內保持有效。

字符串視圖將為 null 當且僅當 str.isNull() .

QAnyStringView:: QAnyStringView (const QString & str )

構造字符串視圖對 str .

str.data() 必須在此字符串視圖對象的壽命內保持有效。

字符串視圖將為 null 當且僅當 str.isNull() .

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

構造字符串視圖對 str 。長度取自 std::size(str) .

std::data(str) 必須在此字符串視圖對象的壽命內保持有效。

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).

另請參閱 isNull () 和 isEmpty ().

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

Returns the last character in the string view.

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串視圖調用此函數，將構成未定義行為。

另請參閱 front () 和 Sizes and Sub-Strings .

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

截取此字符串視圖按 n code points.

如同 *this = first(size() - n) .

注意： 行為未定義當 n < 0 or n > size ().

This function was introduced in Qt 6.5.

另請參閱 sliced (), first (), last (), chopped (), truncate ()，和 Sizes and Sub-Strings .

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

返迴子字符串長度 size () - n 起始於此對象的開頭。

如同 first(size() - n) .

注意： 行為未定義當 n < 0 or n > size ().

This function was introduced in Qt 6.5.

另請參閱 sliced (), first (), last (), chop (), truncate ()，和 Sizes and Sub-Strings .

`[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.

另請參閱 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.

另請參閱 size_bytes ().

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

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

此函數為兼容 STL (標準模闆庫) 提供。

另請參閱 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： 行為未定義當 n < 0 or n > size ().

This function was introduced in Qt 6.5.

另請參閱 last (), sliced (), chopped (), chop (), truncate ()，和 Sizes and Sub-Strings .

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

Returns the first character in the string view.

此函數為兼容 STL (標準模闆庫) 提供。

警告： 在空字符串視圖調用此函數，將構成未定義行為。

另請參閱 back () 和 Sizes and Sub-Strings .

`[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.

另請參閱 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.

另請參閱 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： 行為未定義當 n < 0 or n > size ().

This function was introduced in Qt 6.5.

另請參閱 first (), sliced (), chopped (), chop (), truncate ()，和 Sizes and Sub-Strings .

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

如同 size ().

This function is provided for compatibility with other Qt containers.

另請參閱 size ().

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

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

另請參閱 empty (), isEmpty (), isNull (), size_bytes ()，和 Sizes and Sub-Strings .

`[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.

此函數為兼容 STL (標準模闆庫) 提供。

另請參閱 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： 行為未定義當 pos < 0 or pos > size ().

This function was introduced in Qt 6.5.

另請參閱 first (), last (), chopped (), chop (), truncate ()，和 Sizes and Sub-Strings .

`[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： 行為未定義當 pos < 0, n < 0, or pos + n > size ().

This function was introduced in Qt 6.5.

另請參閱 first (), last (), chopped (), chop (), truncate ()，和 Sizes and Sub-Strings .

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 code points.

如同 *this = first(n) .

注意： 行為未定義當 n < 0 or n > size ().

This function was introduced in Qt 6.5.

另請參閱 sliced (), first (), last (), chopped (), chop ()，和 Sizes and Sub-Strings .

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

調用 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 Class

公共類型

公共函數

靜態公共成員

相關非成員

詳細描述

Compatible Character Types

Sizes and Sub-Strings

成員類型文檔編製

QAnyStringView:: difference_type

QAnyStringView:: size_type

成員函數文檔編製

[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

相關非成員

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 )

內容

`[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