vector的内存分配行为

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> iVec;
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //1个元素， 容器容量为1

    iVec.push_back(1);
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //2个元素， 容器容量为2

    iVec.push_back(2);
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //3个元素， 容器容量为4

    iVec.push_back(3);
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //4个元素， 容器容量为4

    iVec.push_back(4);
    iVec.push_back(5);
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //5个元素， 容器容量为8

    iVec.push_back(6);
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //6个元素， 容器容量为8

    iVec.push_back(7);
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //7个元素， 容器容量为8

    iVec.push_back(8);
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //8个元素， 容器容量为8

    iVec.push_back(9);
    cout << "size: " << iVec.size() << endl;
    cout << "capacity " << iVec.capacity() << endl << endl; //9个元素， 容器容量为16
    /* 结论:
    vector的存在可以使开发者不必关心内存的申请和释放。但是，vector背后的内存分配是按照2的倍数分配内存的。当当前容量对插入元素不够时，分配一块新的内存，这块内存的容量是原vector容量的2倍大小，然后复制旧内存，释放旧内存，可能多次涉及拷贝构造函数和析构函数，而这也正是vector的劣势所在。*/

    return 0;
}