QSpan 类

[constexpr noexcept] auto QSpan:: empty () const

[constexpr noexcept] auto QSpan:: isEmpty () const

Returns whether the span is empty, that is, whether size() == 0 .

These functions do the same thing: empty () is provided for STL compatibility and isEmpty () is provided for Qt compatibility.

另请参阅 size () 和 size_bytes ().

[constexpr] auto QSpan:: sliced ( QSpan < T , E > ::size_type pos ) const

[constexpr] auto QSpan:: subspan ( QSpan < T , E > ::size_type pos ) const

返回 variable-sized span of size size() - pos referencing the remainder of this span after dropping the first pos 元素。

pos must be non-negative.

This span must hold at least pos elements ( E >= pos and size () >= pos ), otherwise the behavior is undefined.

These functions do the same thing: subspan () is provided for STL compatibility and sliced () is provided for Qt compatibility.

另请参阅 subspan (), first (QSpan<T,E>::size_type), and last (QSpan<T,E>::size_type).

[constexpr] auto QSpan:: sliced ( QSpan < T , E > ::size_type pos , QSpan < T , E > ::size_type n ) const

[constexpr] auto QSpan:: subspan ( QSpan < T , E > ::size_type pos , QSpan < T , E > ::size_type n ) const

返回 variable-sized span of size n referencing the n elements of this span starting at pos .

Both pos and n must be non-negative.

This span must hold at least pos + n elements ( E >= pos + n and size () >= pos + n ), otherwise the behavior is undefined.

These functions do the same thing: subspan () is provided for STL compatibility and sliced () is provided for Qt compatibility.

另请参阅 subspan (), first (QSpan<T,E>::size_type), and last (QSpan<T,E>::size_type).

[default] QSpan:: QSpan ()

默认构造函数。

This constructor is only present if E is either zero (0) or std::dynamic_extent . In other words: only fixed-zero-sized or variable-sized spans are default-constructible.

另请参阅 extent and Variable-Size and Fixed-Size Spans .

[constexpr] template <typename Range, QSpan<T, E>::if_compatible_range<Range> = true> QSpan:: QSpan ( Range && r )

Constructs a QSpan referencing the data in the supplied range r .

注意： This constructor participates in overload resolution only if Range is a compatible range .

[constexpr] QSpan:: QSpan ( std::initializer_list < QSpan < T , E > ::value_type > il )

Constructs a QSpan referencing the data in the supplied initializer list il .

注意： This constructor participates in overload resolution only if T is const -qualified.

注意： This constructor is noexcept only if E is std::dynamic_extent .

注意： 若 E 不是 std::dynamic_extent and the size of il 不是 E , the behavior is undefined.

另请参阅 Const and Mutable Spans .

[constexpr] template <typename It, QSpan<T, E>::if_compatible_iterator<It> = true> QSpan:: QSpan ( It first , It last )

Constructs a QSpan referencing the data starting at first and having length ( last - first ).

[first, last) must be a valid range.

注意： This constructor participates in overload resolution only if It is a compatible iterator .

[constexpr] template <typename It, QSpan<T, E>::if_compatible_iterator<It> = true> QSpan:: QSpan ( It first , qsizetype count )

Constructs a QSpan referencing the data starting at first and having length count .

[first, count) must be a valid range.

注意： This constructor participates in overload resolution only if It is a compatible iterator .

[constexpr] auto QSpan:: back () const

Returns a reference to the last element in the span.

The span must not be empty, otherwise the behavior is undefined.

另请参阅 operator[] (), front (), size (), empty ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: begin () const

Returns an interator pointing at the beginning of the span.

因为 QSpan iterators are just pointers, this is the same as calling data ().

另请参阅 end (), cbegin (), rbegin (), crbegin (), data ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: cbegin () const

返回 const_iterator pointing to the beginning of the span.

This will return a read-only iterator even if T 不是 const :

QSpan<int> span = ~~~;
*span.begin() = 42; // OK
*span.cbegin() = 42; // ERROR: cannot assign through a const_iterator
				

另请参阅 cend (), begin (), crbegin (), rbegin (), data ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: cend () const

返回 const_iterator pointing to one past the end of the span.

另请参阅 cbegin (), end (), crend (), rend (), data (), size ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: crbegin () const

返回 const_reverse_iterator pointing to the beginning of the reversed span.

另请参阅 crend (), rbegin (), cbegin (), begin ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: crend () const

返回 const_reverse_iterator pointing to one past the end of the reversed span.

另请参阅 crbegin (), rend (), cend (), end ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: data () const

Returns a pointer to the beginning of the span.

The same as calling begin ().

另请参阅 begin (), front ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: end () const

Returns an iterator pointing to one past the end of the span.

因为 QSpan iterators are just pointers, this it the same as calling data() + size() .

另请参阅 begin (), cend (), rend (), crend (), data (), size ()，和 Const and Mutable Spans .

[constexpr noexcept(...)] template <std::size_t Count> auto QSpan:: first () const

返回 fixed-sized span of size Count referencing the first Count elements of *this .

The span must hold at least Count elements ( E >= Count and size () >= Count ), otherwise the behavior is undefined.

注意： This function is noexcept when subspan_always_succeeds_v<Count> is true .

另请参阅 first (QSpan<T,E>::size_type), last ()，和 subspan ().

[constexpr] auto QSpan:: first ( QSpan < T , E > ::size_type n ) const

返回 variable-sized span of size n referencing the first n elements of *this .

n must be non-negative.

The span must hold at least n elements ( E >= n and size () >= n ), otherwise the behavior is undefined.

另请参阅 first<N> (), last (QSpan<T,E>::size_type), subspan (QSpan<T,E>::size_type), subspan (QSpan<T,E>::size_type, QSpan<T,E>::size_type), and sliced ().

[constexpr] auto QSpan:: front () const

Returns a reference to the first element in the span.

The span must not be empty, otherwise the behavior is undefined.

另请参阅 operator[] (), back (), size (), empty ()，和 Const and Mutable Spans .

[constexpr noexcept(...)] template <std::size_t Count> auto QSpan:: last () const

返回 fixed-sized span of size Count referencing the last Count elements of *this .

The span must hold at least Count elements ( E >= Count and size () >= Count ), otherwise the behavior is undefined.

注意： This function is noexcept when subspan_always_succeeds_v<Count> is true .

另请参阅 last (QSpan<T,E>::size_type), first ()，和 subspan ().

[constexpr] auto QSpan:: last ( QSpan < T , E > ::size_type n ) const

返回 variable-sized span of size n referencing the last n elements of *this .

n must be non-negative.

The span must hold at least n elements ( E >= n and size () >= n ), otherwise the behavior is undefined.

另请参阅 last (), first (QSpan<T,E>::size_type), subspan (QSpan<T,E>::size_type), subspan (QSpan<T,E>::size_type, QSpan<T,E>::size_type), and sliced ().

[constexpr noexcept] auto QSpan:: rbegin () const

返回 reverse_iterator pointing to the beginning of the reversed span.

另请参阅 rend (), crbegin (), begin (), cbegin ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: rend () const

返回 reverse_iterator pointing to one past the end of the reversed span.

另请参阅 rbegin (), crend (), end (), cend ()，和 Const and Mutable Spans .

[constexpr noexcept] auto QSpan:: size () const

Returns the size of the span, that is, the number of elements it references.

另请参阅 size_bytes (), empty ()，和 isEmpty ().

[constexpr noexcept] auto QSpan:: size_bytes () const

Returns the size of the span in bytes, that is, the number of elements multiplied by sizeof(T) .

另请参阅 size (), empty ()，和 isEmpty ().

[constexpr noexcept(...)] template <std::size_t Offset, std::size_t Count> auto QSpan:: subspan () const

Returns a span of size Count referencing the Count elements of this span starting at Offset .

若 *this is a variable-sized span, the return type is a variable-sized span, otherwise it is a fixed-sized span.

This span must hold at least Offset + Count elements ( E >= Offset + Count and size () >= Offset + Count ), otherwise the behavior is undefined.

注意： This function is noexcept when subspan_always_succeeds_v<Offset + Count> is true .

另请参阅 subspan (QSpan<T,E>::size_type, QSpan<T,E>::size_type), subspan(), first (), last ()，和 Variable-Size and Fixed-Size Spans .

[constexpr noexcept(...)] template <std::size_t Offset> auto QSpan:: subspan () const

Returns a span of size E - Offset referencing the remainder of this span after dropping the first Offset 元素。

若 *this is a variable-sized span, the return type is a variable-sized span, otherwise it is a fixed-sized span.

This span must hold at least Offset elements ( E >= Offset and size () >= Offset ), otherwise the behavior is undefined.

注意： This function is noexcept when subspan_always_succeeds_v<Offset> is true .

另请参阅 subspan (QSpan<T,E>::size_type), subspan (), first (), last ()，和 Variable-Size and Fixed-Size Spans .

[constexpr] QSpan < T , E > ::reference QSpan:: operator[] ( QSpan < T , E > ::size_type idx ) const

Returns a reference to the element at index idx in the span.

The index must be in range, that is, idx >= 0 and idx < size (), otherwise the behavior is undefined.

另请参阅 front (), back (), size (), empty ()，和 Const and Mutable Spans .

成员变量文档编制

const std::size_t QSpan:: extent

The second template argument of QSpan<T, E> , that is, E . This is std::dynamic_extent for variable-sized spans .

注意： While all other sizes and indexes in QSpan use qsizetype, this variable, like E , is actually of type size_t , for compatibility with std::span and std::dynamic_extent .

另请参阅 size ().

相关非成员

[noexcept, since 6.8] auto as_bytes ( QSpan < T , E > s )

返回 s 作为 QSpan<const std::byte, E'> whose size () is equal to s.size_bytes() .

若 E is std::dynamic_extent then so is E' 。否则， E' = E * sizeof(T) .

注意： q20::dynamic_extent is a C++17 backport of C++20's std::dynamic_extent .

该函数在 Qt 6.8 引入。

另请参阅 as_writable_bytes (), size_bytes ()，和 Const and Mutable Spans .

[noexcept, since 6.8] auto as_writable_bytes ( QSpan < T , E > s )

返回 s 作为 QSpan<std::byte, E'> whose size () is equal to s.size_bytes() .

若 E is std::dynamic_extent then so is E' 。否则， E' = E * sizeof(T) .

注意： 此函数仅参与重载解析，若 !std::is_const_v<T> .

注意： q20::dynamic_extent is a C++17 backport of C++20's std::dynamic_extent .

该函数在 Qt 6.8 引入。

另请参阅 as_bytes (), size_bytes ()，和 Const and Mutable Spans .