From cppreference.com
size_typesize()constnoexcept;(since C++11)Returns the number of elements in the container, i.e., std::distance(begin(),end()).
Return value
The number of elements in the container.
Complexity
Constant.
Example
Run this code
#include<cassert>#include<unordered_map>intmain(){std::unordered_multimap<int,char>nums{{1,'a'},{1,'b'},{2,'c'},{2,'d'}};assert(nums.size()==4);}See also
checks whether the container is empty
(public member function)
returns the maximum possible number of elements
(public member function)
(C++17)(C++20)
returns the size of a container or array
(function template)