std::span<T,Extent>::subspan - cppreference.com (original) (raw)

Obtains a subview over some consecutive elements of this span, the elements to be included are determined by an element count and an offset.

1. The element count and offset are provided as template arguments, and the subview has a dynamic extent only if both Count and Offset are std::dynamic_extent.

• If Count is std::dynamic_extent, the subview contains all elements starting from the Offsetth.
• Otherwise, the subview contains Count elements starting from the Offsetth.

If Offset <= Extent && (Count == std::dynamic_extent || Count <= Extent - Offset) is false, the program is ill-formed.

| If Offset <= size() && (Count == std::dynamic_extent || Count <= size() - Offset) is false, the behavior is undefined. | (until C++26) | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------- | | If Offset <= size() && (Count == std::dynamic_extent || Count <= size() - Offset) is false: If the implementation is hardened, a contract violation occurs. Moreover, if the contract-violation handler returns under “observe” evaluation semantic, the behavior is undefined. If the implementation is not hardened, the behavior is undefined. | (since C++26) |

1. The element count and offset are provided as function arguments, and the subview always has a dynamic extent.

• If count is std::dynamic_extent, the subview contains all elements starting from the offsetth.
• Otherwise, the subview contains count elements starting from the offsetth.

| If offset <= size() && (count == std::dynamic_extent || count <= size() - offset) is false, the behavior is undefined. | (until C++26) | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------- | | If offset <= size() && (count == std::dynamic_extent || count <= size() - offset) is false: If the implementation is hardened, a contract violation occurs. Moreover, if the contract-violation handler returns under “observe” evaluation semantic, the behavior is undefined. If the implementation is not hardened, the behavior is undefined. | (since C++26) |

[edit] Return value

1. std::span<element_type, FinalExtent>
   (data() + Offset, Count != std::dynamic_extent ? Count : size() - Offset))

[edit] Example

#include #include #include #include #include   void display(std::span 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::puts(""); } }   int main() { char abc[26]; std::ranges::iota(abc, 'A'); display(abc); }

Output:

ABCDEFGHIJKLMNOPQRST BCDEFGHIJKLMNOPQRSTU CDEFGHIJKLMNOPQRSTUV DEFGHIJKLMNOPQRSTUVW EFGHIJKLMNOPQRSTUVWX FGHIJKLMNOPQRSTUVWXY GHIJKLMNOPQRSTUVWXYZ

[edit] See also

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