xfree() -- set ptr to nil (fwd)

["John R. Moore" <jmoore at cygnus dot com>]

Whilst fixing xfree() callsI noticed that xfree() itself has a peculiarity
that needs attention:

The call goes like this:

if (ptr != NULL)
  free(ptr);

Nice, but why not the following:

if (ptr)
  {
     free (ptr);
     prt = NULL);
  }

The latter catches any re-calls to xfree(), unless the compiler sets the
ptr to nil for one (gcc doesn't appear to). Anyhow, it's a good practice
to do this anyhow.

Any opinions?  The only reason I can think not to is to insure that gdb
core dumps on succesive xfree() calls to the same pointer (and hence
insure efficient code, but in that case, why bother with xfree() in the
first place.

John Moore