Question

Why does this code produce the warning?

FILE* my_open_file(char* filename)
{
  FILE* fp=fopen(filename,"r");
  if(fp==NULL)
    {
      perror("Error opening file");
      return -1;
    }
  return fp;
}

• asdf.c: In function ‘my_open_file’:
• asdf.c:9: warning: return makes
  pointer from integer without a cast

fp is already a pointer, and not integer as far as I can see.

Answer 1

The compiler doesn’t like return -1, which is of type int—but my_open_file is supposed to return pointer-to-FILE.

Use return NULL; to signal error.