C++ Vector怎么样释放内存，通过swap（）函数

#include <vector>
#include <iostream>
using namespace std;
main()
{
vector<double>it;
double a[100000];
for(int i=0;i<100000;i++)
{
a[i]=i;
}
cout << "未放元素时容器大小为: " << it.size() << "容器容量为: " << it.capacity() << endl; //未放元素
for(int i=0;i<100000;i++)
{
it. push_back(a[i]);
}
cout << "放元素后容器大小为: " << it.size() << "容器容量为: " << it.capacity() << endl; //放元素
it.clear();
cout << "clear后容器大小为: " << it.size() << "容器容量为: " << it.capacity() << endl; //clear
vector<double>().swap(it);
cout << "swap后容器大小为: " << it.size() << "容器容量为: " << it.capacity() << endl; //swap

return 0;
}