STL中的resize函数与capacity函数

//下面这个程序很有意思，看看发现到第二次的时候svec里面不是1000个元素，这实际上是resize（）函数在作怪！但是最后一步中的capacity如何为3000多的我自己也不太清//楚，如果有知道的可以给我留言：#include <vector>#include <string>#include <iostream>using namespace std;int main(){    vector<string> svec;    svec.reserve(1024);     int n=0;    while(n++<256)   {     string tmp;     svec.push_back(tmp);   }   cout<<"the last size : "<<svec.size()<<endl;   cout<<"the capasity before resize : "<<svec.capacity()<<endl;    svec.resize(svec.size()+svec.size()/2);   cout<<"after resize of the svec:"<<svec.size()<<endl;   cout<<"after read words, capacity : "<<svec.capacity()<<endl;   cout<<endl;   while(n++<1000)   {     string tmp;     svec.push_back(tmp);   }   cout<<"n= "<<n<<endl;   cout<<"the last size : "<<svec.size()<<endl;   cout<<"the capasity before resize : "<<svec.capacity()<<endl;    svec.resize(svec.size()+svec.size()/2);   cout<<"after resize of the svec:"<<svec.size()<<endl;   cout<<"after read words, capacity : "<<svec.capacity()<<endl;   cout<<endl;   while(n++<1048)   {     string tmp;     svec.push_back(tmp);   }   cout<<"the last size : "<<svec.size()<<endl;   cout<<"the capasity before resize : "<<svec.capacity()<<endl;    svec.resize(svec.size()+svec.size()/2);   cout<<"after resize of the svec:"<<svec.size()<<endl;   cout<<"after read  words, capacity : "<<svec.capacity()<<endl;  //最后这一步的capacity（）为什么不是4096？？？ }