■本质
                string是c++风格的字符串，而string本质上是一个类
        ■string和char*区别
                char*是一个指针
                string是一个类，类内部封装了char*，管理这个字符串，是一个char*型的容器
        ■特点
                string类内部封装了很多成员方法
              （例如：查找find，拷贝copy，删除delete，替换replace，插入insert）
                string管理char*所分配的内存，不需要担心复制越界取值越界等，由类内进行负责

#include<iostream>
#include<string>
using namespace std;
void text()  //测试代码
{
  string s1; 
  cout << "s1= "<<s1 << endl;
  const char* s = "hello world"; 
  string s2(s);
  cout << "s2= " << s2 << endl;
  const string& str=s2;
  string s3(str);
  cout << "s3= " << s3 << endl;
  string s4(10, 'a');
  cout << "s4= " << s4 << endl;
}
int main()
{
  text();
}

#include<iostream>
#include<string>
using namespace std;
void text()
{
  string str1; 
  str1 = "hello world";
  cout << "str1= " << str1 << endl;
  string str2; 
  str2= str1;
  cout << "str2= " << str2 << endl;
  string str3;
  str3= 'c';
  cout << "str3= " << str3 << endl;
  string str4;
  str4.assign("hello world");
  cout << "str4= " << str4 << endl;
  string str5;
  str5.assign(str4);
  cout << "str5= " << str5 << endl;
  string str6;
  str6.assign("hello world", 5);
  cout << "str6= " << str6 << endl;
  string str7;
  str7.assign(10, 'a');
  cout << "str7= " << str7 << endl;
}
int main()
{
  text();
}

#include<iostream>
#include<string>
using namespace std;
void text()
{
  string str1 = "你好";
  str1 += "世界";
  cout << "str1= " << str1 << endl;
  string str2 = "你好";
  str2 += 'a';
  cout << "str2= " << str2 << endl;
  string  str3 = "";
  str3 += str1;
  cout << "str3= " << str3 << endl;
  string str4 = "hello";
  str4.append("world");
  cout << "str4= " << str4 << endl;
  string str5 = "hello";
  str5.append("world", 5);
  cout << "str5= " << str5 << endl;
  string str6 = "";
  str6.append(str5);
  cout << "str6= " << str6 << endl;
  string str7 = "";
  str7.append(str6, 0, 10);
  cout << "str7= " << str7 << endl;
}
int main()
{
  text();
}

#include<iostream>
#include<string>
using namespace std;
void text1() //查找
{
  string str1 = "helloworld";
  //find 从左往右查找
  int pos1 = str1.find("o");
  cout << "pos1= " << pos1 << endl;
  //rfind 从右往左查找
  int pos2 = str1.rfind("o");
  cout << "pos2= " << pos2 << endl;
}
void text2() //替换
{
  string str2 = "helloworld";
  str2.replace(1,3,"111");
  cout << "str2= " << str2 << endl;
}
int main()
{
  text1();
  text2();
}

#include<iostream>
#include<string>
using namespace std;
void text()
{
  string str1 = "hello";
  string str2 = "helloworld";
  if (str1.compare(str2) == 0) {
  cout << "str1=str2" <<endl;
  }
  else if (str1.compare(str2) > 0) {
  cout << "str1>str2" << endl;
  }
  else {
  cout << "str1<str2" << endl;
  }
}
int main()
{
  text();
}

#include<iostream>
#include<string>
using namespace std;
void text()
{ 
  //用[ ]来获取字符，并且用[ ]来进行修改
  string str1 = "hello";
  for (int i = 0; i < str1.size(); i++)
  {
  cout << str1[i] ;
  }
  cout << endl;
  str1[0] = 'a';
  cout << str1 << endl;
  //用at来获取字符，并且用at来进行修改
  string str2 = "hello";
  for (int i = 0; i < str2.size(); i++)
  {
  cout << str2.at(i);
  }
  cout << endl;
  str2.at(0) = 'a';
  cout << str2 << endl;
}
int main()
{
  text();
}

#include<iostream>
#include<string>
using namespace std;
void text()
{
  string str1 = "hello";
  str1.insert(5,"world"); //在hello第五个字符后插入字符串world
  cout << "str1= " << str1 << endl;
  str1.insert(5, 1, 'x');
  cout << "str1= " << str1 << endl; //在hello在五个字符后插入字符x
  str1.erase(5, 6);
  cout << "str1= " << str1 << endl; //删除hello第五个字符后的内容
}
int main()
{
  text();
}

#include<iostream>
#include<string>
using namespace std;
void text()
{
  string str1 = "hello";
  string str2 = str1.substr(1, 3);
  cout << "str2 = " << str2 << endl;
}
int main()
{
  text();
}