vector中resize和reserve的区别，代码验证

#include <vector>
using namespace std;

int main()
{
    vector<int>   resizeVect;
    vector<int>   reserveVect;

    resizeVect.resize(50, 2);         //立即分配50个int，每个值为2，默认值为0，如果是class默认构造函数
    vector<int>::iterator iter = resizeVect.begin();
    printf("out put resizeVect value start\n");
    for(; iter != resizeVect.end(); iter++)
    {
        printf("%d ", *iter);
    }
    printf("\nout put resizeVect value end\n");

    printf("resizeVect capacity %d \n", resizeVect.capacity());
    printf("resizeVect size %d \n", resizeVect.size());
    resizeVect.push_back(3);          //添加一个值后,超出了capacity，capacity增加一半
    printf("resizeVect capacity %d \n", resizeVect.capacity());
    printf("resizeVect size %d \n", resizeVect.size());

    printf("\r\n \r\n");

    reserveVect.reserve(50);          //预留capacity为50，但是没有内存，当然也不会有值
    iter = reserveVect.begin();
    printf("out put resizeVect value start\n");
    for(; iter != reserveVect.end(); iter++)
    {
        printf("%d ", *iter);
    }
    printf("\nout put resizeVect value end\n");

    printf("reserveVect capacity %d \n", reserveVect.capacity());
    printf("reserveVect size %d \n", reserveVect.size());
    reserveVect.push_back(3);         //添加一个值后，没有超出capacity，capacity保持不变，size+1
    printf("reserveVect capacity %d \n", reserveVect.capacity());
    printf("reserveVect size %d \n", reserveVect.size());

    system("pause");
    return 1;

}