From cppreference.com
Defined in header
Defined in header
inlinenamespace/* unspecified */{inlineconstexpr/* unspecified */ssize=/* unspecified */;}(since C++20)
(customization point object)Call signature
template<classT>requires/* see below */constexprautossize(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
of which t denotes the (possibly
) result object as E:
If ranges::size(t) is ill-formed, ranges::ssize(E) is also ill-formed.
Otherwise, let Signed be
<decltype(ranges::size(t))>: If
is wider than Signed, ranges::ssize(E) is
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
of a
class type. See
for details.
Notes
If ranges::ssize(e) is valid for an expression e, the return type is a
.
Example
Run this code
#include<array>#include<iostream>#include<ranges>#include<type_traits>intmain(){std::arrayarr{1,2,3,4,5};autos=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 Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++20 ranges::size worked for some non-range types but ranges::ssize did not made work See also
(C++20)
returns an integer equal to the size of a range
(customization point object)
(C++20)
specifies that a range knows its size in constant time
(concept)
(C++20)
returns the distance between an iterator and a sentinel, or between the beginning and end of a range
(algorithm function object)
(C++17)(C++20)
returns the size of a container or array
(function template)