std::span::subspan

template< std::ptrdiff_t Offset,
          std::ptrdiff_t Count = std::dynamic_extent >
constexpr std::span<element_type, E /* see below */> subspan() const;

constexpr std::span<element_type, std::dynamic_extent> 
    subspan( std::ptrdiff_t Offset,
             std::ptrdiff_t Count = std::dynamic_extent ) const;

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 either less than zero or greater than size();
• Count is less than zero and not std::dynamic_extent;
• Offset + Count is greater than size().

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.

See also