Question

I have a function that returns the first n characters until a specified character is reached. I want to pass a ptr to be set to the next word in the string; how do I accomplish this? Here is my current code.

char* extract_word(char* ptrToNext, char* line, char parseChar)
// gets a substring from line till a space is found
// POST: word is returned as the first n characters read until parseChar occurs in line
//      FCTVAL == a ptr to the next word in line
{
   int i = 0;
   while(line[i] != parseChar && line[i] != '\0' && line[i] != '\n')
   {
      i++;
   }

   printf("line + i + 1: %c\n", *(line + i + 1));  //testing and debugging

   ptrToNext = (line + i + 1);    // HELP ME WITH THIS! I know when the function returns
                                  //   ptrToNext will have a garbage value because local
                                  //   variables are declared on the stack

   char* temp = malloc(i + 1);

   for(int j = 0; j < i; j++)
   {
      temp[j] = line[j];
   }
   temp[i+1] = '\0';

   char* word = strdup(temp);
   return word;
}

Answer 1

You’d pass an argument that is a pointer to pointer to char; then in the function, you can change the value of the pointed-to pointer. In other words

char * line = ...;
char * next;
char * word = extract_word(&next, line, 'q');

And inside your function…

// Note that "*" -- we're dereferencing ptrToNext so
// we set the value of the pointed-to pointer.
*ptrToNext = (line + i + 1);