From cppreference.com
size_typesize()const;(noexcept since C++11)
(constexpr since C++20)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
The following code uses size to display the number of elements in a std::vector<int>:
Run this code
#include<cassert>#include<vector>intmain(){std::vector<int>nums;assert(nums.size()==0);nums={1,2,3,4};assert(nums.size()==4);}See also
returns the number of elements that can be held in currently allocated storage
(public member function)
checks whether the container is empty
(public member function)
returns the maximum possible number of elements
(public member function)
changes the number of elements stored
(public member function)
(C++17)(C++20)
returns the size of a container or array
(function template)