Re: Question about ECPGset_noind_null() and ECPGis_noind_null()

Tom Lane <tgl@sss.pgh.pa.us>

From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Dunstan <andrew@dunslane.net>
Cc: Boszormenyi Zoltan <zb@cybertec.at>, Michael Meskes <meskes@postgresql.org>, pgsql-hackers@postgresql.org, Hans-Juergen Schoenig <hs@cybertec.at>
Date: 2009-11-19T20:51:12Z
Lists: pgsql-hackers
Andrew Dunstan <andrew@dunslane.net> writes:
> Boszormenyi Zoltan wrote:
>> Is it *really* a bug? I recalled a comment from my C teacher
>> in '92 or '93 about this exact issue, that the prefix/postfix
>> increment/decrement operators are executed in the
>> statement in an implementation-defined order, 

> Not if they come after a short-circuit operator such as && - after all, 
> that's what short-circuit evaluation implies. If the left hand operand 
> of && is false the right hand should not be evaluated at all.

Yes.  && is a sequence point and the compiler is not allowed to move
side-effects across a sequence point.  What your C teacher was warning
you against was things like
	a[i] = i++;
'=' is not a sequence point so it's undefined which array index
will be stored into.

			regards, tom lane