C++ std::string::compare()用法及代碼示例

compare()是字符串類的公共成員函數。它將字符串對象(或子字符串)的值與其參數指定的字符序列進行比較。
compare()可以為每個字符串處理多個參數，以便可以通過其索引和長度指定子字符串。

返回類型：compare()返回一個整數值，而不是布爾值。

string::compare(的不同語法)：

1. 語法1：比較字符串* this和字符串str。

   int string::compare (const string& str) const
   返回：
   0: if both strings are equal.
   A value < 0:if *this is shorter than str or,
   first character that doesn't match is smaller than str.
   A value > 0: if *this is longer than str or,
   first character that doesn't match is greater
   

   // CPP code for demonstrating  
   // string::compare (const string& str) const 
     
   #include<iostream> 
   using namespace std; 
     
   void compareOperation(string s1, string s2) 
   { 
       // returns a value < 0 (s1 is smaller then s2) 
       if((s1.compare(s2)) < 0) 
           cout << s1 << " is smaller than " << s2 << endl; 
     
       // returns 0(s1, is being comapared to itself) 
       if((s1.compare(s1)) == 0) 
           cout << s1 << " is equal to " << s1 << endl; 
       else
           cout << "Strings didn't match "; 
         
   } 
     
   // Driver Code 
   int main() 
   { 
       string s1("Geeks"); 
       string s2("forGeeks"); 
       compareOperation(s1, s2); 
         
       return 0;  
   }

   輸出：

   Geeks is smaller than forGeeks
   Geeks is equal to Geeks
   

2. 語法2：最多比較字符串* this的len個字符，以索引idx和字符串str開頭。

   int string::compare (size_type idx, size_type len, const string& str) const
   Throws out_of_range if index > size().
   

   // CPP code to demonstrate  
   // int string::compare (size_type idx, size_type len,  
   // const string& str) const 
     
   #include<iostream> 
   using namespace std; 
     
   void compareOperation(string s1, string s2) 
   { 
       // Compares 5 characters from index number 3 of s2 with s1 
       if((s2.compare(3, 5, s1)) == 0) 
           cout << "Here, "<< s1 << " are " << s2; 
     
       else
           cout << "Strings didn't match "; 
   } 
   // Driver Code 
   int main() 
   { 
       string s1("Geeks"); 
       string s2("forGeeks"); 
       compareOperation(s1, s2); 
          
     return 0;  
   }

   輸出：

   Here, Geeks are forGeeks
   

3. 語法3：比較最多*個字符串的len個字符，此字符以索引idx開頭，最多比較以字符串str_idx開頭的字符串str的str_len個字符。

   int string::compare (size_type idx, size_type len, const string& 
   str, size_type str_idx, size_type str_len) const
   Throws out_of_range if idx > size().
   Throws out_of_range if str_idx > str.size().
   

   // CPP code to demonstrate  
   // int string::compare (size_type idx, size_type len, const string&  
   // str, size_type str_idx, size_type str_len) const 
     
   #include<iostream> 
   using namespace std; 
     
   void compareOperation(string s1, string s2) 
   { 
       // Compares 5 characters from index number 0 of s1 with 
       // 5 characters from index 3 of s2 
       if((s1.compare(0, 5, s2, 3, 5)) == 0) 
           cout << "Welcome to " << s1 << s2 << " World"; 
     
       else
           cout << "Strings didn't match "; 
   } 
   // Driver Code 
   int main() 
   { 
       string s1("Geeks"); 
       string s2("forGeeks"); 
       compareOperation(s1, s2); 
          
     return 0;  
   }

   輸出：

   Welcome, to GeeksforGeeks World
   

4. 語法4：將字符串* this的字符與C-string cstr的字符進行比較。

   int string::compare (const char* cstr) const

   // CPP code to demonstrate 
   // int string::compare (const char* cstr) const 
     
   #include<iostream> 
   using namespace std; 
     
   void compareOperation(string s1, string s2) 
   { 
       // returns < 0 (s1 < "GeeksforGeeks") 
       if((s1.compare("GeeksforGeeks")) < 0) 
           cout << s1 << " is smaller than string " << "GeeksforGeeks";  
     
       //returns 0 (s2 is "forgeeks") 
       if((s2.compare("forGeeks")) == 0) 
           cout << endl << s2 << " is equal to string " << s2;  
     
       else
           cout << "Strings didn't match "; 
         
   } 
   // Driver Code 
   int main() 
   { 
       string s1("Geeks"); 
       string s2("forGeeks"); 
       compareOperation(s1, s2); 
          
     return 0;  
   }

   輸出：

   Geeks is smaller than string GeeksforGeeks
   forGeeks is equal to string forGeeks
   

5. 語法5：最多比較字符串* this的len個字符，從索引idx到C-string cstr的所有字符。

   int string::compare (size_type idx, size_type len, const char* cstr) const
   

   請注意，cstr可能不是空指針(NULL)。

   // CPP code to demonstrate  
   // int string::compare (size_type idx, size_type len,  
   // const char* cstr) const 
   #include<iostream> 
   using namespace std; 
     
   void compareOperation(string s1) 
   { 
       // Compares 5 characters from 0 index of s1 with "Geeks" 
       if((s1.compare(0, 5, "Geeks")) == 0) 
           cout << s1 << " are " << "awesome people";  
         
       else
           cout << "Strings didn't match "; 
      
   } 
     
   // Driver Code 
   int main() 
   { 
       string s1("Geeks"); 
       compareOperation(s1); 
          
     return 0;  
   }

   輸出：

   Geeks are awesome people
   

6. 語法6：最多比較字符串* this的len個字符，從索引idx開始，以字符數組chars的chars_len字符開頭。

   int string::compare (size_type idx, size_type len, const char* chars, 
   size_type chars_len)const

   請注意，字符必須至少包含chars_len字符。字符可以具有任意值。因此，“ \ 0”沒有特殊含義。

   // CPP code to demonstrate  
   // int string::compare (size_type idx, size_type len,  
   // const char* chars, size_type chars_len)const 
     
   #include<iostream> 
   using namespace std; 
     
   void compareOperation(string s1, string s2) 
   { 
       // Compares 5 characters from 0 index of s1 with  
       // 5 characters of string "Geeks" 
       if((s1.compare(0, 5, "Geeks", 5)) == 0) 
           cout << "This is " << s1 <<  s2 ;  
      
       else
           cout << "Strings didn't match "; 
   } 
     
   // Driver Code 
   int main() 
   { 
       string s1("Geeks"); 
       string s2("forGeeks"); 
       compareOperation(s1, s2); 
          
     return 0;  
   }

   輸出：

   This is GeeksforGeeks