Question

I’m using this code inside a function to get the shortest and longest string in a file. The length variables and strings are declared outside the loop. The int variables are correctly updated inside and outside the loop, but the char* variables are only updated correctly inside.

on the last printf statement I get:

the string Zulia
 is the longest in a2.txt and has 18 chars

the string Zulia
 is the shortest in a2.txt and has 5 chars

What’s going on here?

fp1 = fopen(fileName, "r"); 

        if (fp1 == NULL)
        {
            printf("Error while opening file: %s\n",fileName); 
            exit (1);
        } 



            int lengthLongestString=1;
            int lengthShortestString=1000; 

            int lengthActualString=0;

            char *longestString; 
            char *shortestString; 
            char *currentString;



        while (fgets(fileLine,  SIZE_OF_LINE, fp1) != NULL)     
        {

            if(((strcmp(fileLine, "\n") != 0)) && (strcmp(fileLine, "\r\n") != 0)){     //Validates against storing empty lines

                lineas[numeroLineas++] = strdup(fileLine);          


                             lengthActualString=strlen(fileLine); 
                             currentString=fileLine;


                             if (lengthActualString>lengthLongestString){



                                  lengthLongestString = lengthActualString;

                                  longestString=fileLine;
                                  printf("the longest string now is %s \n",longestString);

                 } 

                 else if (lengthActualString<lengthShortestString){

                     lengthShortestString = lengthActualString;


                                 shortestString=fileLine; 
                     printf("the shortest string now is %s \n",shortestString);         
                } // END IF


            }// END IF

          } //END WHILE 

          printf("the string %s is the longest in %s and has %d chars\n",longestString, fileName, lengthLongestString );
          printf("the string %s is the shortest in %s and has %d chars\n",shortestString, fileName, lengthShortestString);

Answer 1

longestString and shortestString are pointers. They point somewhere. If you change the contents of somewhere, of course, the stuff the pointers point to has changed 🙂

You need to allocate memory for longestString and shortestString (or define them as arrays rather than pointers) and copy the chars there.