C++ String //string字符串查找和替换 比较 存取 修改单个字符 插入和删除 string字串

//string字符串查找和替换  比较  存取 修改单个字符 插入和删除  string字串
#include <iostream>
#include<string>

using namespace std;
//查找

void test01()
{
    string str1 = "abcdefg";

    int pos =str1.find("de");

    if (pos == -1)
    {
        cout << "没有找到<<endl;" <<endl;
    }
    else
    {
        cout << "找到字符串的位置，pos=" << pos << endl;
    }

    cout << "pos = " << pos << endl;

    //rfind 和 find 区别
    //rfind从右往左查找    find从左往右查找
    pos = str1.rfind("de");
    cout << "pos" << pos << endl;



}

//替换
void test02()
{
    string str1 = "abcdefg";
    
    //从1号位置起 3个字符 替换为“1111”
    str1.replace(1, 3, "2222");
    cout << "str1 = " << str1 << endl;
}

//比较 
 // = 0    >1    <-1
void test03()
{
    string str3 = "xhello";
    string str4 = "hellllo";

    if (str3.compare(str4) == 0)
    {
        cout << "str1等于 str2" << endl;
    }
    else if (str3.compare(str4) > 0)
    {
        cout << "str3 大于 str4 " << endl;
    }
    else
    {
        cout << "str3 小于 str4 " << endl;
    }

}

//string 字符存取
void test04()
{
    string str = "hello";
    //cout << "str = " << str << endl;

    //第一种通过[]访问单个字符
    for (int i = 0; i < str.size(); i++)
    {
        cout << str[i] << " ";
    }
    cout << endl;

    //第二种通过at访问单个字符
    for (int i = 0; i < str.size(); i++)
    {
        cout << str.at(i) << " ";
    }
    cout << endl;

    //修改单个字符
    str[0] = 'x';
    cout << "str = " << str << endl;

    str.at(1) = 'z';
    cout << "str = " << str << endl;

}

//string 插入和删除

void test05()
{
    string str8 = "hello";

    //插入
    str8.insert(1, "111");
    cout << "str8 = " << str8 << endl;

    //删除
    str8.erase(1, 3);
    cout << "str8 = " << str8 << endl;

}

//string 求字串
void test6()
{
    string str = "ancdef";

    string subStr = str.substr(1, 3);

    cout << "subStr = " << subStr << endl;
}

//使用操作
void test7()
{
    string email = "zhangsan@qq.com";
    //从邮件地址中 获取 用户信息

    int pos = email.find("@"); //8
    cout << "emial pos = " << pos << endl;

    string userName = email.substr(0, pos);
    cout << "userName = " << userName << endl;
}

int main()
{
    //test01();
    //test02();
    //test03();

    //test04();

    //test05();
    //test6();
    test7();
}