std::size

 

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Iterator operations advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	Range access begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

Defined in header <iterator>
template < class C > constexpr auto size( const C& c ) -> decltype(c.size());	(1)	(since C++17)
template < class T, size_t N > constexpr size_t size( const T (&array)[N] ) noexcept;	(2)	(since C++17)

Returns the size of the given container c or array array.

1) Returns c.size().

2) Returns N.

Parameters

c	-	a container with a size method
array	-	an array of arbitrary type

Return value

The size of c or array

Notes

In addition to being included in <iterator>, std::size is guaranteed to become available if any of the following headers are included: <array>, <deque>, <forward_list>, <list>, <map>, <regex>, <set>, <span>(since C++20), <string>, <string_view>, <unordered_map>, <unordered_set>, and <vector>.

Possible implementation

First version
template <class C> constexpr auto size(const C& c) -> decltype(c.size()) { return c.size(); }
Second version
template <class T, std::size_t N> constexpr std::size_t size(const T (&array)[N]) noexcept { return N; }

Example

Run this code

#include <iostream>
#include <vector>
#include <iterator>
 
int main() 
{
    std::vector<int> v = { 3, 1, 4 };
    std::cout << std::size(v) << '\n'; 
 
    int a[] = { -5, 10, 15 };
    std::cout << std::size(a) << '\n';
}

Output:

3
3