Re: [chrony-dev] GCC issue

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

On Tue, 21 Jan 2014, Dale R. Worley wrote:

> > From: Bill Unruh <unruh@xxxxxxxxxxxxxx>
>
> > > Apparently there is no sequence point with the | operator and the
> > > compiler is free to use any order.
> > >
> > > http://en.wikipedia.org/wiki/Sequence_point
> >
> > Lets hope that
> > r=(fprintf()<0) ;
> > r|=fclose()
> > does not get optimized away by the compiler, and then one runs into the same
> > problem.
>
> My understanding is that the fclose() is required to be executed
> regardless of the value of r at that point -- "|" is not a
> short-circuit operator.
>
> I would like to see the code as:
>
> > r=(fprintf()<0) ;
> > r|=(fclose() == EOF);
>
> fclose() returns 0 on success and EOF on failure, and it's generally
> not a good idea to use "|" on values whose bit-pattern you do not
> understand.

But with the bitwise or, if ANY bit is non zero, the result is nonzero, which
is what you want. So in this case it is fine. No matter what fclose returns,
unless it is zero it is an error.


> Dale

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