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Date: Sun, 23 Nov 2014 14:39:02 -0500
From: Rich Felker <>
Subject: Re: [PATCH] Add stdatomic.h for clang>=3.1 and gcc>=4.1

On Sun, Nov 23, 2014 at 07:01:24PM +0100, Jens Gustedt wrote:
> Am Sonntag, den 23.11.2014, 11:37 -0500 schrieb Rich Felker:
> > But it's a variably-modified type, so sizeof and typeof evaluate the
> > expression when their operand is of this type.  Thus, all you have
> > to do is make an array of objects of this type, and then refer to
> > arr[i++]. This will be an expression with variably-modified type,
> yes, but not a VLA
> > and the evaluation will have unwanted side effects.
> No, I don't think it is evaluated, says:
>   If the type of the operand is a variable length array type, the
>   operand is evaluated;
> observe that it says VLA, and not VM type.
>   otherwise, the operand is not evaluated and the result is an integer
>   constant.
> There are no exception for other VM types. To deduce the size for our
> case here, an evaluation isn't necessary.
> (Hoping that the __typeof__ stuff follows the same rules.)

OK, thanks for clarifying this. In that case I think we're safe as
long as __typeof__ follows the same rules.


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