C++ Deque shrink_to_fit()

void shrink_to_fit(); 

#include <iostream>
#include<deque>
using namespace std;
int main()
{
 deque<int> d={1,2,3,4,5};
 cout<<"size :"<<d.size();
 d.resize(3);
 cout<<'\n';
 cout<<"size:"<<d.size();
 d.shrink_to_fit();
 return 0;
}