Basic usage of string in C++

Basic usage of string in C++

1. Initialization

• There are two main ways to initialize, one is to use the equal sign for copy initialization, and the other is to directly initialize without using the equal sign.

•     string str1;               //生成空字符串
      string str2("123456789");  //生成"1234456789"的复制品
      string str3("12345", 0, 3);//结果为"123"
      string str4("0123456", 5);  //结果为"01234"
      string str5(5, '1');       //结果为"11111"
      string str6(str2, 2);      //结果为"3456789"
  

2. Insert

    string str = "123456789";
    //在字符串str的数组下标为6的位置上面插入2个字符x
    str.insert(6,2,'x'); //结果为str:123456xx789
	 string str1("x");  
str.insert(6,str1); //结果为str:123456x789

    string str10 = "1234589";
    string str11 = "67";
     //在str的数组下标为5的位置插入 str11从0位置开始的2个数
    str10.insert(5,str11,0,2);//结果为str10:123456789
	str10.insert(5,str11,2);//表示插入str11开始的两个数

• Note: If you directly use the following code to insert, an error will be reported and an error will be prompted.

  error: invalid conversion from 'char' to 'const char ' *, needs to be defined as const type.

  str.insert(6,'x'); 
  

3. Replacement

• Replacement is similar to insertion

•     string str = "123456789";
      string str12 = "321";
      //删除str从0开始的三个数，然后插入str12从0开始的三个数
      str.replace(0,3,str12,0,3);//结果为str:321456789
   //删除str从0开始的三个数，然后插入str12
      str.replace(0,3,str12);//结果为str:321456789
  

4. Add

• To add, use the keyword append or directly use '+' connection.

      string str = "123456789";
      string str12 = "321";
    str.append(str12,0,3);//str:123456789321
  

5. Assignment

//s.assign(n,ch)             将n个ch字符赋值给字符串s
//s.assign(str,pos,n)        将字符串str从pos开始的n个字符赋值给字符串s

6. Delete

   string str = "123456789";
      str.erase(8,1);//结果为str:12345678

7. Exchange

    string str10 = "1234589";
    string str11 = "67";
      swap(str10,str11);//str10:67  str11:1234589
 swap(str11[0],str11[1]);//str11:76

8. Reversal

string str = "abcdefghijklmn";
reverse(str.begin(),str.end());       // str = "nmlkjihgfedcba"

9. Search

• rfind is to find the position of the last occurrence (opposite of find).

    string str20 = "123456789";
    string key = "2";
    //s.find(str)            查找字符串str在当前字符串s中第一次出现的位置
    int pos1 = str20.find(key);  //pos1:1 ,未查找到返回-1
//从3位置开始查找
int pos1 = str20.find(key,3);  //pos1:-1,未查找到返回-1

• find_xxx_of function

• string str = "The early birds catch the warm";            //长度30
  string key = "aeiou";
  
  

  // s.find_first_of(str)                查找字符串str中的任意字符在当前字符串s中第一次出现的位置
  int pos1 = str.find_first_of(key);              C  // 2
  
  //s.find_first_of(str,pos)             查找字符串str中的任意字符在当前字符串s的[pos,end]中第一次出现的位置
  int pos2 = str.find_first_of(key, 10);            // 11
  
  //s.find_first_of(cstr,pos,n)          查找字符串str前n个任意字符在当前字符串s的[pos,end]中第一次出现的位置
  //此处不可将"aeiou"替换为key
  int pos3 = str.find_first_of("aeiou", 7, 2);      // 17
  
  //s.find_first_of(ch,pos)              查找字符ch在当前字符串s的[pos,end]中第一次出现的位置
  int pos4 = str.find_first_of('r', 0);             // 6