QAnyStringView 類

QAnyStringView 類提供 Latin-1、UTF-8 或 UTF-16 的統一字符串視圖，采用隻讀子集的 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

• 所有成員列錶，包括繼承成員
• 棄用成員
• QAnyStringView 屬於 用於字符串數據的類 .

此類 強烈可比較 .

此類 強烈可比較 采用 char16_t， QChar , const char16_t *, const char *, QByteArray , QByteArrayView , QString , QStringView , QUtf8StringView ，和 QLatin1StringView .

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 (const Char & ch )
	QAnyStringView (const Char (&)[N] string )
	QAnyStringView (const Char * str )
	QAnyStringView (const Container & str )
	QAnyStringView (const QByteArray & str )
	QAnyStringView (const QString & str )
	QAnyStringView (std::nullptr_t)
	QAnyStringView (const Char * first , const Char * last )
	QAnyStringView (const Char * str , qsizetype len )
(從 6.9 起) QString	arg (Args &&... args ) const
QChar	back () const
(從 6.5 起) void	chop (qsizetype n )
(從 6.5 起) QAnyStringView	chopped (qsizetype n ) const
const void *	data () const
bool	empty () const
(從 6.5 起) QAnyStringView	first (qsizetype n ) const
QChar	front () const
bool	isEmpty () const
bool	isNull () const
(從 6.5 起) QAnyStringView	last (qsizetype n ) const
qsizetype	length () const
(從 6.8 起) qsizetype	max_size () const
qsizetype	size () const
qsizetype	size_bytes () const
(從 6.8 起) QAnyStringView &	slice (qsizetype pos , qsizetype n )
(從 6.8 起) QAnyStringView &	slice (qsizetype pos )
(從 6.5 起) QAnyStringView	sliced (qsizetype pos ) const
(從 6.5 起) QAnyStringView	sliced (qsizetype pos , qsizetype n ) const
QString	toString () const
(從 6.5 起) 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)
QAnyStringView	fromArray (const Char (&)[Size] string )

相關非成員

bool	operator!= (const QAnyStringView & lhs , const QAnyStringView & rhs )
bool	operator< (const QAnyStringView & lhs , const QAnyStringView & rhs )
(從 6.7 起) QDebug	operator<< (QDebug d , QAnyStringView s )
bool	operator<= (const QAnyStringView & lhs , const QAnyStringView & rhs )
bool	operator== (const QAnyStringView & lhs , const QAnyStringView & rhs )
bool	operator> (const QAnyStringView & lhs , const QAnyStringView & rhs )
bool	operator>= (const QAnyStringView & lhs , const QAnyStringView & rhs )

詳細描述

QAnyStringView 引用它不擁有的字符串連續部分。它充當所有種類字符串的接口類型，不需要構造 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.

例如，

QAnyStringView str = funcReturningQString(); // return value is a temp
					

would leave str referencing the deleted temporary (which constitutes undefined behavior). This is particularly true for the single-character constructors:

QAnyStringView ch = u' '; // u' ' is a temporary
// oops, ch references deleted temporary
					

In both cases, the solution is to "pin" the temporary to an lvalue and only then create a QAnyStringView from it:

const auto r = funcReturningQString();
QAnyStringView str = r; // ok, `r` outlives `str`
const auto sp = u' ';
QAnyStringView ch = sp; // ok, `sp` outlives `ch`
					

However, using QAnyStringView as the interface type that it is intended to be is always safe, provided the called function's documentation is not asking for a longer lifetime:

void func(QAnyStringView s);
func(u' ');
func(functionReturningQString());
					

This is why QAnyStringView supports these conversions in the first place.

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 為 文字類型 .

兼容字符類型

QAnyStringView 接受各種字符類型的字符串：

• char (有符號和無符號兩者)
• char8_t (僅 C++20)
• char16_t
• wchar_t (在此是 16 位類型，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 ).

The following character types are only supported by the single-character constructor:

• QLatin1Char
• QChar::SpecialCharacter
• wchar_t (where it's a 32-bit type, i.e. Unix) (since 6.10)
• char32_t

These character types are internally decomposed into a UTF-16 sequence (using QChar::fromUcs4 () for the last).

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).

另請參閱 使用哪個字符串類？ , QUtf8StringView ，和 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 noexcept] QAnyStringView:: QAnyStringView ()

構造 null 字符串視圖。

另請參閱 isNull ().

[constexpr noexcept] template <typename Char, QAnyStringView::if_compatible_char<Char> = true> QAnyStringView:: QAnyStringView (const Char & ch )

Constructs a string view on the single character ch . The length is usually 1 (but see below).

In general, you must assume that a QAnyStringView thus created will start to reference stale data at the end of the full-expression , when temporaries are deleted. That means that using it to pass a single character to a QAnyStringView-taking function is ok and safe (as long as the function documentation doesn't ask for a lifetime longer than the initial call):

int to_int(QAnyStringView);
int res = to_int(u'9'); // OK, data stays around for the duration of the call
					

But keeping the object around longer is undefined behavior:

QAnyStringView ch = u'9';
int res = to_int(ch); // (silent) ERROR: ch references deleted data
					

If you need this, prefer

const auto nine = u'9';
QAnyStringView ch(nine); // ok, references `nine`, which outlives `ch`
int res = to_int(ch); // 9
					

The above is true for all directly supported 兼容字符類型 .

若 ch is not one of these types, but merely converts to QChar ，如 QChar::SpecialCharacter or QLatin1Char , the QAnyStringView will bind to a temporary object that will have been deleted at the end of the full expression, just like in the second example.

若 ch cannot be represented in a single UTF-16 code unit (e.g. because it's a char32_t value), this constructor decomposes ch into two UFT-16 code units. The resulting QAnyStringView will have a size () of 2 in that case, and the temporary buffer in which the decomposition is stored is deleted at the end of the full-expression, similar to

[](char32_t ch, auto &&tmp = QChar::fromUcs4(ch)) {
    return QAnyStringView(tmp);
}
					

The equivalent safe version in this case would be

const auto decomposed = QChar::fromUcs4(ch);
QAnyStringView ch(decomposed);
					

另請參閱 QChar::fromUcs4 () 和 兼容字符類型 .

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

構造字符串視圖按字符串文字 string 。視圖覆蓋數組，直到第 1 個 Char(0) 被遇到，或 N ，以先到的為準。若需要完整數組，使用 fromArray () 代替。

string 必須在此字符串視圖對象的壽命內保持有效。

約束

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

另請參閱 兼容字符類型 .

[constexpr noexcept] 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。

約束

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

另請參閱 isNull () 和 兼容字符類型 .

[constexpr noexcept] template <typename Container, QAnyStringView::if_compatible_container<Container> = true> QAnyStringView:: QAnyStringView (const 容器 & 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。

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).

約束

Participates in overload resolution only if Container is a container with a compatible character type as value_type .

另請參閱 isNull () 和 isEmpty ().

[noexcept] 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() .

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

構造 null 字符串視圖。

另請參閱 isNull ().

[constexpr] template <typename Char, QAnyStringView::if_compatible_char<Char> = true> 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.

約束

Participates in overload resolution only if Char is a compatible character type.

另請參閱 isNull () 和 兼容字符類型 .

[constexpr] template <typename Char, QAnyStringView::if_compatible_char<Char> = true> 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 .

約束

Participates in overload resolution only if Char is a compatible character type.

另請參閱 isNull () 和 兼容字符類型 .

[since 6.9] template <typename... Args> QString QAnyStringView:: arg ( Args &&... args ) const

Replaces occurrences of %N in this string with the corresponding argument from args . The arguments are not positional: the first of the args 替換 %N with the lowest N (all of them), the second of the args the %N with the next-lowest N etc.

Args can consist of anything that implicitly converts to QAnyStringView .

該函數在 Qt 6.9 引入。

另請參閱 QString::arg (Args&&...).

[constexpr] QChar QAnyStringView:: back () const

返迴字符串視圖中的最後一個字符。

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 大小和子字符串 .

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

截取此字符串視圖按 n 代碼點。

如同 *this = first(size() - n) .

注意： 行為未定義當 n < 0 or n > size ().

該函數在 Qt 6.5 引入。

另請參閱 sliced (), first (), last (), chopped (), truncate (), slice ()，和 大小和子字符串 .

[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 ().

該函數在 Qt 6.5 引入。

另請參閱 sliced (), first (), last (), chop (), truncate (), slice ()，和 大小和子字符串 .

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

比較字符串視圖 lhs with the string view rhs 並返迴負整數若 lhs 小於 rhs ，正整數若大於 rhs ，和 0 若它們相等。

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 noexcept] 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 noexcept] 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:: 第一 ( 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 ().

該函數在 Qt 6.5 引入。

另請參閱 last (), sliced (), chopped (), chop (), truncate (), slice ()，和 大小和子字符串 .

[static constexpr noexcept] template <typename Char, size_t Size, QAnyStringView::if_compatible_char<Char> = true> QAnyStringView QAnyStringView:: fromArray (const Char (&)[ Size ] string )

Constructs a string view on the full character string literal string , including any trailing Char(0) . If you don't want the null-terminator included in the view then you can chop () it off when you are certain it is at the end. Alternatively you can use the constructor overload taking an array literal which will create a view up to, but not including, the first null-terminator in the data.

string 必須在此字符串視圖對象的壽命內保持有效。

This function will work with any array literal if Char is a compatible character type. The compatible character types are: QChar , ushort , char16_t and (on platforms, such as Windows, where it is a 16-bit type) wchar_t .

[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 大小和子字符串 .

[constexpr noexcept] 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 noexcept] 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 ().

該函數在 Qt 6.5 引入。

另請參閱 first (), sliced (), chopped (), chop (), truncate (), slice ()，和 大小和子字符串 .

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

如同 size ().

This function is provided for compatibility with other Qt containers.

另請參閱 size ().

[constexpr noexcept, since 6.8] qsizetype QAnyStringView:: max_size () const

此函數為兼容 STL (標準模闆庫) 提供。

It returns the maximum number of elements that the string view can theoretically represent. In practice, the number can be much smaller, limited by the amount of memory available to the system.

注意： The returned value is calculated based on the currently used character type, so calling this function on two different views may return different results.

該函數在 Qt 6.8 引入。

[constexpr noexcept] 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 大小和子字符串 .

[constexpr noexcept] 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 6.8] QAnyStringView &QAnyStringView:: slice ( qsizetype pos , qsizetype n )

Modifies this string view to start at position pos , extending for n 代碼點。

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

該函數在 Qt 6.8 引入。

另請參閱 sliced (), first (), last (), chopped (), chop (), truncate ()，和 大小和子字符串 .

[constexpr, since 6.8] QAnyStringView &QAnyStringView:: slice ( qsizetype pos )

Modifies this string view to start at position pos , extending to its end.

注意： 行為未定義當 pos < 0 or pos > size ().

這是重載函數。

該函數在 Qt 6.8 引入。

另請參閱 sliced (), first (), last (), chopped (), chop (), truncate ()，和 大小和子字符串 .

[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 ().

該函數在 Qt 6.5 引入。

另請參閱 first (), last (), chopped (), chop (), truncate (), slice ()，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： 行為未定義當 pos < 0, n < 0, or pos + n > size ().

該函數在 Qt 6.5 引入。

另請參閱 first (), last (), chopped (), chop (), truncate (), slice ()，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 代碼點。

如同 *this = first(n) .

注意： 行為未定義當 n < 0 or n > size ().

該函數在 Qt 6.5 引入。

另請參閱 sliced (), first (), last (), chopped (), chop ()，和 大小和子字符串 .

[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
    });
}