c++ 将容量设置为容器的长度（shrink_to_fit）

#include <iostream>
#include <vector>
using namespace std;
int main ()
{
    vector<int> myvector (25);
    cout << "1. capacity of myvector: " << myvector.capacity() << '\n';
    for (int i=0; i<20; i++) myvector[i]=i;
    myvector.resize(10);
    cout << "2. capacity of myvector: " << myvector.capacity() << '\n';
    for (int i=0; i<25; i++) cout << myvector[i]<<endl;
    cout<<"\n"<<endl;
    myvector.shrink_to_fit();
    for (int i=0; i<10; i++) cout << myvector[i]<<endl;
    cout << "3. capacity of myvector: " << myvector.capacity() << '\n';
    return 0;
}