shrink_to_fit   //只适用于vector,string,deque
capacity  reserve    //只适用于vector,string 

c.shrink_to_fit()   //请将capacity()减少为与size相同大小
c.capacity()        //不重新分配内存空间的话，c可以保存多少元素
c.reserve(n)        //分配至少能容纳n个元素的内存空间

capacity和size

#include<iostream>
#include<vector>

using namespace std;

int main()
{
    vector<int> ivec;
    //size应该为0；capacity的值依赖于具体实现
    cout<<" ivec : size: "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;
    //向ivec添加24个元素
    for(vector<int>::size_type ix=0 ; ix != 24 ; ++ix)
        ivec.push_back(ix);

    //size应该为24；capacity应该大于或等于24，具体值依赖于标准库实现
    cout<<" ivec: size: "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;
}

 ivec: size: 0 capacity: 0

 ivec: size: 24 capacity: 32

ivec.reserve(50);       //将capacity至少设定为50，可能会更大
    //size应该为24；capacity应该大于等于50，具体值依赖于标准库
    cout<<" ivec :size: "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

 ivec: size: 24 capacity: 50

    //添加元素用光多余容量
    while(ivec.size() != ivec.capacity())
            ivec.push_back(0);
    //capacity应该未改变,size和capacity不相等
    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

 ivec: size: 50 capacity: 50

 ivec.push_back(42); //添加一个元素
    //size的值现在应是51；capacity应该大于51，看以来的标准库
     cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

 ivec: size: 51 capacity: 100

    ivec.shrink_to_fit();   //要求归还内存
    //size未变capacity应该看具体实现
    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

 ivec: size: 51 capacity: 51

    vector<int> ivec;
    //size应该为0；capacity的值依赖于具体实现
    //添加256个单词
    for(vector<int>::size_type ix=0 ; ix != 256 ; ++ix)
    {
        ivec.push_back(ix);
    }
    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

    ivec.resize(500);   //吧它capacity设定为至少500
    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

    ivec.shrink_to_fit();       //返回内存

    for(int ix=0 ; ix != 12 ; ++ix)
        ivec.push_back(ix);

    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

/**
* 功能:vector对象时如何增长的
* 时间:2014年6月12日07:43:54
* 作者:cutter_point
*/

/*
shrink_to_fit   //只适用于vector,string,deque
capacity  reserve    //只适用于vector,string

c.shrink_to_fit()   //请将capacity()减少为与size相同大小
c.capacity()        //不重新分配内存空间的话，c可以保存多少元素
c.reserve(n)        //分配至少能容纳n个元素的内存空间
*/

#include<iostream>
#include<vector>

using namespace std;

int main()
{

    /*
    vector<int> ivec;
    //size应该为0；capacity的值依赖于具体实现
    cout<<" ivec : size: "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;
    //向ivec添加24个元素
    for(vector<int>::size_type ix=0 ; ix != 24 ; ++ix)
        ivec.push_back(ix);

    //size应该为24；capacity应该大于或等于24，具体值依赖于标准库实现
    cout<<" ivec: size: "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

    ivec.reserve(50);       //将capacity至少设定为50，可能会更大
    //size应该为24；capacity应该大于等于50，具体值依赖于标准库
    cout<<" ivec :size: "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

    //添加元素用光多余容量
    while(ivec.size() != ivec.capacity())
            ivec.push_back(0);
    //capacity应该未改变,size和capacity不相等
    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

    ivec.push_back(42); //添加一个元素
    //size的值现在应是51；capacity应该大于51，看以来的标准库
     cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

    ivec.shrink_to_fit();   //要求归还内存
    //size未变capacity应该看具体实现
    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;
        */

    vector<int> ivec;
    //size应该为0；capacity的值依赖于具体实现
    //添加256个单词
    for(vector<int>::size_type ix=0 ; ix != 256 ; ++ix)
    {
        ivec.push_back(ix);
    }
    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

    ivec.resize(500);   //吧它capacity设定为至少500
    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;

    ivec.shrink_to_fit();       //返回内存

    for(int ix=0 ; ix != 12 ; ++ix)
        ivec.push_back(ix);

    cout<<" ivec : size : "<<ivec.size()
        <<" capacity: "<<ivec.capacity()<<endl;



    return 0;
}