Date: Tue, 27 Oct 92 13:20:35 EST
From: DJ Delorie <dj AT athena DOT ctron DOT com>
To: turnbull AT ecolan DOT sbs DOT ohio-state DOT edu
Cc: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: FREEing NULL pointers

> I thought you were always mod ANSI allowed to free a NULL pointer, but
> not an uninitialized or previously free'd one.

Nobody said that djgpp was ANSI.  The sources for free() come from the
BSD free'd sources - no modifications at all.

> This is a serious bug, if true, with the standard library.   Freeing a NULL
> pointer is legal and covered in the definition of the function free.

The SunOS 4.1 man pages state that free() takes a "a pointer to a
block previously allocated by malloc(), calloc(), realloc(), malloc(),
or memalign()."  It also states that free() sets errno to EINVAL if
the pointer passed does not fall into that category (that's a bug in
djgpp).  It does not explicitly state that it's legal to free NULL.

Assuming that free can handle NULL is invalid, unless you are sure
that it's *supposed* to be ANSI compliant.  Trying to free NULL also
implies that your program isn't checking the validity of pointers it
is dealing with.

DJ
dj AT ctron DOT com
Life is a banana.