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

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< cpp‎ | container‎ | span

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( std::size_t Offset, std::size_t 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`.).

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

- `Offset` is greater than `size()`;
- `Count` is not `std::dynamic_extent` and `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

first | obtains a subspan consisting of the first N elements of the sequence (public member function)
last | obtains a subspan consisting of the last N elements of the sequence (public member function)

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