linux-kernel - Re: Stray nulls when reading from AF

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Date:	Fri, 7 Sep 2007 13:52:51 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	David Miller <davem@...emloft.net>
cc:	anders.blomdell@...trol.lth.se, linux-kernel@...r.kernel.org
Subject: Re: Stray nulls when reading from AF_UNIX sockets


On Sep 6 2007 12:23, David Miller wrote:
>>     return copied ? : err;
>>   }
>> 
>> Shouldn't this read:
>> 
>>     return copied ? copied : err;
>> 
>> Or am I missing something?
>
>These two statements are equivalent, the first version is
>a shorthand allowed by gcc.

Not only that. With x?x:z, x is evaluated twice,
while with x?:z, x is only evaluated once. That's for stuff when you 
want to, say [dumb example follows],

size_t my_read(..) {
    return read(..) ? : -1
}

and the only other way would be to use a temporary,

size_t my_read(..) {
	size_t x = read(..);
	return x ? x : -1;
}

gcc should be smart enough to also do optimization in the second case..


	Jan
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