请你回答一下STL里resize和reserve的区别？

Answer 1

resize()：改变当前容器内含有元素的数量(size())，eg: vector v; v.resize(len);v的size变为len,如果原来v的size小于len，那么容器新增（len-size）个元素，元素的值为默认为0.当v.push_back(3);之后，则是3是放在了v的末尾，即下标为len，此时容器是size为len+1；

 

#include <iostream>
#include <vector>
using namespace std;
int main() {
    vector<int> a;
    a.reserve(100);
    a.resize(50);
    cout<<a.size()<<"  "<<a.capacity()<<endl;
        //50  100
    a.resize(150);
    cout<<a.size()<<"  "<<a.capacity()<<endl;
        //150  200
    a.reserve(50);
    cout<<a.size()<<"  "<<a.capacity()<<endl;
        //150  200
    a.resize(50);
    cout<<a.size()<<"  "<<a.capacity()<<endl;
        //50  200    
}