while reading an old thread I found this bit of code. I was wondering if anyone could explain to me the components of the function declaration. I tried using this code, but I got a warning when i tried to compile it, and a link error while attempting to run it. The warning states that Callback is undefined. And the link error states that there is an unresolved external symbol _Callback. I think Prelude is the one who supplied this code, so maybe that's who I need to ask in order to clarify.

Code:
int ReadLines(const char *Filename, ReadLineFunc Callback) 
{
  FILE *fp = fopen(Filename, "r");
  char	hex2[512];
  char *copy;
  
  if(fp == NULL) {
    fprintf(stderr,"Error, file is not found. \n");
    return -1;
  }

  /* Read each line and print it out */
  while(fgets(hex2, 512, fp) != NULL) {
    copy = malloc ( strlen ( hex2 ) + 1 );
    if ( copy != NULL ) {
      strcpy ( copy, hex2 );
      Callback(copy);
      free ( copy );
      copy = NULL;
    }
  }

  fclose(fp);

  return 0;
}