一 代码

#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;class TEST{
public:TEST(){std::cout << "construct t" << std::endl;}
};int main()
{std::cout << "hello,world" <<std::endl;std::vector<TEST> vt;vt.reserve(5);int n = vt.size();std::cout << n << std::endl;vt.resize(10);n = vt.size();std::cout << n << std::endl;return 0;
}

// 输出
hello,world
0
construct t
construct t
construct t
construct t
construct t
construct t
construct t
construct t
construct t
construct t
10
请按任意键继续. . .

二 区别

reserve: 仅改变容量，不改变元素数量和值；不调用构造函数；
resive: 改变容量，改变元素数量，调用构造函数