vector的reserve方法

#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector<int> v1(10);

    std::cout << "v1 size : " << v1.size() << std::endl;
    std::cout << "v1 capacity : " << v1.capacity() << std::endl;
    
    v1.reserve(20);
    
    std::cout << "v1 size : " << v1.size() << std::endl;
    std::cout << "v1 capacity : " << v1.capacity() << std::endl;
    
    return 0;
}

此函数用来改变容量大小，运行结果如下：

 

 capacity扩大到了20，size不变。