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String Pattern Matching: Write a function that checks for a given pattern at the end of a given string

Posted by tekpool on October 15, 2006

String Pattern Matching: Write a function that checks for a given pattern at the end of a given string

In other words, Write a function, a variant of strstr that takes in 2 strings str1 and str2 and returns true if str2 occurs at the end of the string str1, and false otherwise.

bool str_str_end(char * str1, char * str2) 
{ 
        // Store the base pointers of both strings 
        char* beginStr1 = str1; 
        char* beingStr2 = str2; 

       // Move to the end of the strings 
        while(*str1++); 

        while(*str2++); 

        for(; *str1 == *str2; str1--, Str2--) 
       { 
       If( str2 == beginStr2 
                          || str1 == beingStr1) 
            { 
            break; 
            } 
       } 
       return    If(*str1 == *str2 
                    && str2 == beginStr2 
                    && *str1 != 0); 
}

Save the base addresses of the strings and then traverse to the end of the stings. To check if the string str2 occurs at the end of the string str1, start comparing characters from the end of the strings and move backwards. The function returns true when

  1. All the characters in str1 match all the characters in str2 from the end.
  2. The pointer str2 reaches back at the beginning of the string, which means there is nothing more to be compared
  3. The strings are not empty.

The above conditions are required so that the loops do not run in an infinite loop.

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Posted in Algorithms, C++, General, Microsoft, Pattern Matching, Progamming Languages, Strings | 2 Comments »