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Date: Tue, 27 May 2008 09:45:18 +0200
From: Marc Olzheim <marcolz@stack.nl>
To: Krassimir Slavchev <krassi@bulinfo.net>
Message-ID: <20080527074518.GA2593@zlo.nu>
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Cc: FreeBSD <freebsd-stable@freebsd.org>
Subject: Re: shmat() return values?
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On Mon, May 26, 2008 at 08:14:38PM +0300, Krassimir Slavchev wrote:
> Hello,
> 
> When I try:
> 
> if ((*shm = shmat(shmid, NULL, 0)) == -1)
> 
> The gcc complains with:
> warning: comparison between pointer and integer
> 
> shmat() is declared in shm.h as:
> void *shmat(int, const void *, int);
> 
> but 'man 4 shmat;
> 
> RETURN VALUES
>      Upon success, shmat() returns the address where the segment is
> attached;
>      otherwise, -1 is returned and errno is set to indicate the error.
> 
> 
> What is the correct return value on failure, -1 or NULL?
> I think it should be NULL?

The return value is a void pointer, with value equivalent to -1,
so (void *)-1

So you can replace it with:

if ((*shm = shmat(shmid, NULL, 0)) == (void*)-1)

Marc