std::ranges::ssize - cppreference.com (original) (raw)

| Defined in header | | | | ----------------------------------------------------------------------------------------------------------- | | ------------------------------------------ | | Defined in header | | | | inline namespace /* unspecified */ { inline constexpr /* unspecified */ ssize = /* unspecified */; } | | (since C++20) (customization point object) | | Call signature | | | | template< class T > requires /* see below */ constexpr auto ssize( T&& t ); | | (since C++20) |

Calculates the number of elements in t in constant time, and converts the result to a signed type.

Given the subexpression of which t denotes the (possibly materialized) result object as E:

• If ranges::size(t) is ill-formed, ranges::ssize(E) is also ill-formed.
• Otherwise, let Signed be _[make-signed-like-t](../ranges.html#make-signed-like-t "cpp/ranges")_ <decltype(ranges::size(t))>:
  • If std::ptrdiff_t is wider than Signed, ranges::ssize(E) is expression-equivalent to static_cast<std::ptrdiff_t>(ranges::size(t)).
  • Otherwise, ranges::ssize(E) is expression-equivalent to static_cast<Signed>(ranges::size(t)).

Customization point objects

The name ranges::ssize denotes a customization point object, which is a const function object of a literal semiregular class type. See CustomizationPointObject for details.

[edit] Notes

If ranges::ssize(e) is valid for an expression e, the return type is a signed-integer-like type.

[edit] Example

#include #include #include #include   int main() { std::array arr{1, 2, 3, 4, 5}; auto s = std::ranges::ssize(arr);   std::cout << "ranges::ssize(arr) = " << s << '\n' << "ranges::ssize is " << (std::is_signed_v<decltype(s)> ? "signed" : "unsigned") << '\n';   std::cout << "reversed arr: ";   for (--s; s >= 0; --s) std::cout << arr[s] << ' ';   std::cout << "\n" "s = " << s << '\n'; }

Output:

ranges::ssize(arr) = 5 ranges::ssize is signed reversed arr: 5 4 3 2 1 s = -1

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also

| | returns an integer equal to the size of a range(customization point object)[edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | specifies that a range knows its size in constant time (concept) [edit] | | | returns the distance between an iterator and a sentinel, or between the beginning and end of a range(algorithm function object)[edit] | | | returns the size of a container or array (function template) [edit] |