string

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

int main()
{
    //创建对象
    string s1,s2,s;
    //赋值
    s1="Hello";
    s2=" World";
    s="Hello World";

    //尾部添加
    //'+'  '+='   可添加字符，字符串
    s1 += s2;               //s1="Hello World"
    s1 +=" World";          //s1="Hello World"
    s1 +='W';               //s1="HelloW"
    //append()    只能添加字符串
    s1.append(s2);          //s1="Hello World"
    s1.append(" World");    //s1="Hello World"
    //push_back()  只能添加字符
    s1.push_back('W');       //s1="HelloW"

    //插入 insert()
    s1.insert(0,"World ");    //s1="World Hello"
    s1.insert(0,s2);        //s1=" WorldHello"

    //删除 erase()
    s.erase(5,3);          //s="Hellorld"
    s.erase(s.begin()+2,s.end()-3);  //s="Herld"

    //查找 find() 返回下标值，从0开始
    s.find('o');           //返回4
    s.find("llo");         //返回2,返回第一个字符出现的下标

    //替换  replace()
    s.replace(6,5,"good");    //从第六个开始，将连续的五个字符替换成 good  s="Hello good"
    s.replace(s.find('W'),5,"good");      //s="Hello good"

    //返回长度
    s.size();
    s.length();       //均返回11

    //判断是否为空
    s.empty();        //空，返回1，否则返回0

    //反向排序 reverse()
    reverse(s.begin(),s.end());     //s="dlroW olleH"
    
    return 0;
}

比较  compare()  比对方大返回1，小返回-1，相等返回0

    string str1="green apple";
    string str2="red apple";
    string str3="apple";
    if(str3.compare("apple") == 0)
        cout << str3 << " is an apple!" << endl;
    if(str1.compare(str2) !=0)
        cout << str1 << " is not " << str2 <<endl;
    if(str1.compare(6,5, "apple") == 0)
        cout << "still, " << str1 << " is an apple!" << endl;
    if(str2.compare(str2.size()-5, 5, "apple") == 0)
        cout << "and " << str2 << " is an apple!" <<endl;
    if(str1.compare(6, 5, str2, 4, 5) == 0)
        cout << "therefore, both are apples!" << endl;

string对象作为vector元素  类似字符串数组

    vector <string> str;
    str.push_back("dog");
    str.push_back("and");
    str.push_back("cat");
    cout << s[0] <<endl;             //返回dog
    cout << s[1] <<endl;             //返回and
    cout << s[0][2] <<endl;          //返回g
    cout << s[2][1] <<endl;          //返回a
    cout << s[0].size() <<endl;      //返回3