From cppreference.com
size_typesize()constnoexcept;(since C++23)Returns the number of elements in the container adaptor. Equivalent to: return
.keys.size().
Return value
The number of elements in the container adaptor.
Complexity
Constant.
Example
Run this code
#include<cassert>#include<flat_map>intmain(){std::flat_map<int,char>nums{{1,'a'},{1,'b'},{2,'c'},{2,'d'}};assert(nums.size()==2);}See also
checks whether the container adaptor is empty
(public member function)
(C++17)(C++20)
returns the size of a container or array
(function template)
returns the maximum possible number of elements
(public member function)