std::span<T,Extent>::subspan
template< std::size_t Offset, std::size_t Count = std::dynamic_extent > constexpr std::span<element_type, E /* see below */> subspan() const; |
(1) | |
constexpr std::span<element_type, std::dynamic_extent> subspan( size_type Offset, size_type Count = std::dynamic_extent ) const; |
(2) |
Obtains a span that is a view over the Count
elements of this span starting at offset Offset
. If Count
is std::dynamic_extent
, the number of elements in the subspan is size() - offset
(i.e., it ends at the end of *this
.).
(1) is ill-formed if.
-
Offset
is greater thanExtent
, or -
Count
is notstd::dynamic_extent
andCount
is greater thanExtent - Offset
.
The behavior is undefined if either Offset
or Count
is out of range. This happens if.
-
Offset
is greater thansize()
, or -
Count
is notstd::dynamic_extent
andCount
is greater thansize() - Offset
.
The extent E
of the span returned by (1) is determined as follows:
- If
Count
is notstd::dynamic_extent
,Count
; - Otherwise, if
Extent
is notstd::dynamic_extent
,Extent - Offset
; - Otherwise,
std::dynamic_extent
.
Return value
The requested subspan r
, such that r.data() == this->data() + Offset
. If Count
is std::dynamic_extent
, r.size() == this->size() - Offset
; otherwise r.size() == Count
.
Example
#include <algorithm> #include <cstdio> #include <numeric> #include <ranges> #include <span> void display(std::span<const char> abc) { const auto columns{ 20U }; const auto rows{ abc.size() - columns + 1 }; for (auto offset{ 0U }; offset < rows; ++offset) { std::ranges::for_each( abc.subspan(offset, columns), std::putchar ); std::putchar('\n'); } } int main() { char abc[26]; std::iota(std::begin(abc), std::end(abc), 'A'); display(abc); }
Output:
ABCDEFGHIJKLMNOPQRST BCDEFGHIJKLMNOPQRSTU CDEFGHIJKLMNOPQRSTUV DEFGHIJKLMNOPQRSTUVW EFGHIJKLMNOPQRSTUVWX FGHIJKLMNOPQRSTUVWXY GHIJKLMNOPQRSTUVWXYZ
See also
obtains a subspan consisting of the first N elements of the sequence (public member function) |
|
obtains a subspan consisting of the last N elements of the sequence (public member function) |
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