std::span<T,Extent>:: subspan

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 ).

The behavior is undefined if either Offset or Count is out of range. This happens if

• Offset is greater than size() , or
• Count is not std::dynamic_extent and Count is greater than size ( ) - Offset .

The extent E of the span returned by (1) is determined as follows:

• If Count is not std::dynamic_extent , Count ;
• Otherwise, if Extent is not std::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);
}

ABCDEFGHIJKLMNOPQRST
BCDEFGHIJKLMNOPQRSTU
CDEFGHIJKLMNOPQRSTUV
DEFGHIJKLMNOPQRSTUVW
EFGHIJKLMNOPQRSTUVWX
FGHIJKLMNOPQRSTUVWXY
GHIJKLMNOPQRSTUVWXYZ

See also