Patch #2 to Pcomm v1.1

[Paul Allen]

In article <416 at quintus.UUCP> ok at quintus.UUCP (Richard A. O'Keefe) writes:
>In article <13900004 at osiris.cso.uiuc.edu> hood at osiris.cso.uiuc.edu writes:
>>This patch will fix the problem that some people are having with 
>>seqmentation faults (although I'm not convinced the problem isn't
>>in their compiler).
>
>It isn't.  It's the famous *NULL bug.
>
>>! 	if (*lock_path != NULL && lock_path != NULL) {
>
>This only tests whether lock_path is legal *after* trying to use it!

I've now seen a couple postings about this bug, but nobody has got it
right yet!  What has been missed is that C makes no guarantee about the
order of expression evaluation.  The only safe way to perform this test
is using two nested if statements.

I'll be quiet now.
Paul

-- 
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Paul L. Allen                       | paula at boeing.com
Boeing Advanced Technology Center   | ...!uw-beaver!ssc-vax!bcsaic!paula