get_line_from_instream()

<piece_of_code> .c

char * get_line_from_instream(void) {
  char * line = malloc(100), * linep = line;
  size_t lenmax = 100, len = lenmax;
  int c;

  if (line == NULL)
    return NULL;

  for (;;) {
    c = fgetc(stdin);
    if (c == EOF)
      break;

    if (--len == 0) {
      len = lenmax;
      char * linen = realloc(linep, lenmax *= 2);

      if (linen == NULL) {
        free(linep);
        return NULL;
      }
      line = linen + (line - linep);
      linep = linen;
    }

    if ((*line++ = c) == '\n')
      break;
  }
  *line = '\0';
  return linep;
}

For a better understanding of line26 I've found this reference: http://denniskubes.com/2012/08/14/do-you-know-what-p-does-in-c/