assert(*n - nchars_avail == read_pos - *lineptr);
assert((*lineptr + *n) == (read_pos + nchars_avail));
getstr (lineptr, n, stream, terminator, offset)     char **lineptr;     size_t *n;     FILE *stream;     char terminator;     int offset;{  int nchars_avail;		/* Allocated but unused chars in *LINEPTR.  */  char *read_pos;		/* Where we're reading into *LINEPTR. */  int ret;  if (!lineptr || !n || !stream)    return -1;  if (!*lineptr)    {      *n = MIN_CHUNK;      *lineptr = malloc (*n);      if (!*lineptr)	return -1;    }  nchars_avail = *n - offset;  read_pos = *lineptr + offset;  for (;;)    {      register int c = getc (stream);      /* We always want at least one char left in the buffer, since we	 always (unless we get an error while reading the first char)	 NUL-terminate the line buffer.  */      assert(*n - nchars_avail == read_pos - *lineptr);      if (nchars_avail < 2)	{	  if (*n > MIN_CHUNK)	    *n *= 2;	  else	    *n += MIN_CHUNK;	  nchars_avail = *n + *lineptr - read_pos;	  *lineptr = realloc (*lineptr, *n);	  if (!*lineptr)	    return -1;	  read_pos = *n - nchars_avail + *lineptr;	  assert(*n - nchars_avail == read_pos - *lineptr);	}      if (c == EOF || ferror (stream))	{	  /* Return partial line, if any.  */	  if (read_pos == *lineptr)	    return -1;	  else	    break;	}      *read_pos++ = c;      nchars_avail--;      if (c == terminator)	/* Return the line.  */	break;    }  /* Done - NUL terminate and return the number of chars read.  */  *read_pos = '\0';  ret = read_pos - (*lineptr + offset);  return ret;}