std::string的resize()与reserve()的区别

std::string的resize()与reserve()的区别:

resize()：改变的是size()与capacity()的大小

(1)、比原来的变小之后，后面的会被截断

(2)、比原来的变大之后，后面的会被填充新的东西，不同的编译器可能会不同

reserve()：改变的只是capacity()的大小

程序如下：

#include <math.h>
#include <stdio.h>
#include <string>
#include<iostream>

using namespace std;

int main()
{
    std::string s1("hello");
    std::cout << "s1=" << s1 << " s1.size=" << s1.size() << " s1.capacity=" << s1.capacity() << endl;

    std::cout << "after resize to 2" << endl;
    s1.resize(2); //尺寸由5改变为2，多余字符被截掉了,只剩下he
    std::cout << "s1=" << s1 << " s1.size=" << s1.size() << " s1.capacity=" << s1.capacity() << endl;

    std::cout << "after resize to 100" << endl;
    s1.resize(100);//尺寸由2改变为100,后面的数据被填充了98个a
    std::cout << "s1=" << s1 << " s1.size=" << s1.size() << " s1.capacity=" << s1.capacity() << endl;

    std::cout << "\n";
    std::cout << "===================================================================" << endl;
    std::cout << "\n";

    std::string s2("hello");
    std::cout << "s2=" << s2 << " s2.size=" << s2.size() << " s2.capacity=" << s2.capacity() << endl;

    std::cout << "after reserve to 20" << endl;
    s2.reserve(20);  //只改变capacity()的大小，其他的不变
    std::cout << "s2=" << s2 << " s2.size=" << s2.size() << " s2.capacity=" << s2.capacity() << endl;

    std::cout << "after reserve to 2" << endl;
    s2.reserve(2);   //只改变capacity()的大小，其他的不变
    std::cout << "s2=" << s2 << " s2.size=" << s2.size() << " s2.capacity=" << s2.capacity() << endl;

    return 0;
}

结果：

std::string的resize()与reserve()的区别