容器vector的一点疑问：capacity()函数不可控？

#include "stdafx.h"

#include <vector>

#include <iostream>



using std::cout;

using std::endl;

using std::vector;



template<typename ContainersType>

void printContainersData(ContainersType containers)

{

	ContainersType::iterator begin = containers.begin();

	ContainersType::iterator end = containers.end();

	for (; begin!=end; begin++)

	{

		cout<<*begin<<' ';

	}

	cout<<endl;

}



int _tmain(int argc, _TCHAR* argv[])

{

	//定义空Vector

	vector<short>vContainers1;//vContainers1.capacity()结果为13 为什么?

	//vector<short>vContainers1(4);//vContainers1.capacity()结果为19 为什么?

	//vector<short>vContainers1(5);//vContainers1.capacity()结果为15 为什么?



	//向Vector中输入元素

	for (short index = 0; index<10; index++)

	{

		vContainers1.push_back(index);

	}



	cout<<"为空Vector赋值，结果为：\n";

	cout<<"vContainers1：";

	printContainersData(vContainers1);	

	cout<<vContainers1.capacity());//容器为空时capacity()不可控?

	cout<<endl;



	return 0;

}