#include<iostream>
using namespace std;

#include<string>
//string的构造函数
//
//* `string(); `                          //创建一个空的字符串 例如: string str;
//`string(const char* s); `            //使用字符串s初始化
//* `string(const string& str); `    //使用一个string对象初始化另一个string对象
//* `string(int n, char c); `           //使用n个字符c初始化 

void test01() {
    string s1;//默认构造

    const char* str = "hello world";
    string s2(str);

    cout << "s2= " << s2 << endl;

    string s3(s2);

    cout << "s3= " << s3 << endl;
    string s4(10,'a');
    cout << "s4= " << s4 << endl;
}
int main() {

    test01();
    system("pause");
    return 0;
}

#include<iostream>
using namespace std;
#include<string>

//string 赋值操作
//*`string& operator=(const char* s); `             //char*类型字符串 赋值给当前的字符串
//* `string& operator=(const string &s); `         //把字符串s赋给当前的字符串
//* `string& operator=(char c); `                          //字符赋值给当前的字符串
//* `string& assign(const char *s); `                  //把字符串s赋给当前的字符串
//* `string& assign(const char *s, int n); `     //把字符串s的前n个字符赋给当前的字符串
//* `string& assign(const string &s); `              //把字符串s赋给当前字符串
//* `string& assign(int n, char c); `                  //用n个字符c赋给当前字符串

void test01()
{
    string str1;
    str1 = "hello world";
    cout << "str1=" << str1 << endl;

    string str2;
    str2 = str1;
    cout << "str2=" << str2<< endl;

    string str3;
    str3 = 'a';
    cout << "str3=" << str3 << endl;

    string str4;
    str4.assign("hello C++");
    cout << "str4=" << str4 << endl;


    string str5;
    str5.assign("hello C++",5);
    cout << "str5=" << str5 << endl;

    string str6;
    str6.assign(str5);
    cout << "str6=" << str6 << endl;

    string str7;
    str7.assign(10,'w');
    cout << "str7=" << str7 << endl;
}
int main()
{
    test01();
    system("pause");
    return 0;

}

#include<iostream>
using namespace std;
#include<string>
//字符串拼接

//* `string& operator+=(const char* str); `                   //重载+=操作符
//* `string& operator+=(const char c); `                         //重载+=操作符
//* `string& operator+=(const string& str); `                //重载+=操作符
//* `string& append(const char *s); `                               //把字符串s连接到当前字符串结尾
//* `string& append(const char *s, int n); `                 //把字符串s的前n个字符连接到当前字符串结尾
//* `string& append(const string &s); `                           //同operator+=(const string& str)
//* `string& append(const string &s, int pos, int n); `/ / 字符串s中从pos开始的n个字符连接到字符串结尾


void test01() 
{
    string str1 = "我";
    str1 += "爱玩游戏";

    cout << "str1=" << str1 << endl;

    str1 += ':';

    cout << "str1=" << str1 << endl;

    string str2 = "LOL DNF";

    str1 += str2;
    cout << "str1=" << str1 << endl;

    string str3 = "I";
    str3.append("love");
    cout << "str3=" << str3 << endl;

    str3.append(" game abcde",4);
    cout << "str3=" << str3 << endl;

    str3.append(str2);
    cout << "str3=" << str3 << endl;

    str3.append(str2,0,3);
    cout << "str3=" << str3 << endl;
}
int main()
{
    test01();
    system("pause");
    return 0;

}

```C++
//查找和替换
void test01()
{
    //查找
    string str1 = "abcdefgde";

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

    if (pos == -1)
    {
        cout << "未找到" << endl;
    }
    else
    {
        cout << "pos = " << pos << endl;
    }
    

    pos = str1.rfind("de");

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

}

void test02()
{
    //替换
    string str1 = "abcdefgde";
    str1.replace(1, 3, "1111");

    cout << "str1 = " << str1 << endl;
}

int main() {

    //test01();
    //test02();

    system("pause");

    return 0;
}
```

总结：

* find查找是从左往后，rfind从右往左
* find找到字符串后返回查找的第一个字符位置，找不到返回-1
* replace在替换时，要指定从哪个位置起，多少个字符，替换成什么样的字符串

//字符串比较
void test01()
{

    string s1 = "hello";
    string s2 = "aello";

    int ret = s1.compare(s2);

    if (ret == 0) {
        cout << "s1 等于 s2" << endl;
    }
    else if (ret > 0)
    {
        cout << "s1 大于 s2" << endl;
    }
    else
    {
        cout << "s1 小于 s2" << endl;
    }

}

int main() {

    test01();

    system("pause");

    return 0;
}
```

总结：字符串对比主要是用于比较两个字符串是否相等，判断谁大谁小的意义并不是很大

```C++
void test01()
{
    string str = "hello world";

    for (int i = 0; i < str.size(); i++)
    {
        cout << str[i] << " ";
    }
    cout << endl;

    for (int i = 0; i < str.size(); i++)
    {
        cout << str.at(i) << " ";
    }
    cout << endl;


    //字符修改
    str[0] = 'x';
    str.at(1) = 'x';
    cout << str << endl;
    
}

int main() {

    test01();

    system("pause");

    return 0;
}
```

总结：string字符串中单个字符存取有两种方式，利用 [ ] 或 at

#### 3.1.8 string插入和删除

**功能描述：**

* 对string字符串进行插入和删除字符操作

**函数原型：**

* `string& insert(int pos, const char* s);  `                //插入字符串
* `string& insert(int pos, const string& str); `        //插入字符串
* `string& insert(int pos, int n, char c);`                //在指定位置插入n个字符c
* `string& erase(int pos, int n = npos);`                    //删除从Pos开始的n个字符 





**示例：**

```C++
//字符串插入和删除
void test01()
{
    string str = "hello";
    str.insert(1, "111");
    cout << str << endl;

    str.erase(1, 3);  //从1号位置开始3个字符
    cout << str << endl;
}

int main() {

    test01();

    system("pause");

    return 0;
}
```

**总结：**插入和删除的起始下标都是从0开始











#### 3.1.9 string子串

**功能描述：**

* 从字符串中获取想要的子串



**函数原型：**

* `string substr(int pos = 0, int n = npos) const;`   //返回由pos开始的n个字符组成的字符串




**示例：**

```C++
//子串
void test01()
{

    string str = "abcdefg";
    string subStr = str.substr(1, 3);
    cout << "subStr = " << subStr << endl;

    string email = "hello@sina.com";
    int pos = email.find("@");
    string username = email.substr(0, pos);
    cout << "username: " << username << endl;

}

int main() {

    test01();

    system("pause");

    return 0;
}
```

**总结：**灵活的运用求子串功能，可以在实际开发中获取有效的信息