From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Thu, 9 Apr 2015 23:07:13 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Message-ID: <20150409210713.GH20752@hermes.click-hack.org>
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Subject: Re: [Xenomai] Why does mqueue.h define mqd_t as unsigned
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To: Phil Mitchell <p.mitch@gmail.com>
Cc: Xenomai Mailing List <xenomai@xenomai.org>

On Thu, Apr 09, 2015 at 04:52:26PM -0400, Phil Mitchell wrote:
> Dear All,
> 
> mqueue.h defines mqd_t as an unsigned long. The function mq_open returns
> type mqd_t and states that -1 is returned in case of error.
> 
> Is mqd_t defined incorrectly or am I missing something?

The specification does not say what mqd_t should be and says that
mq_open returns (mqd_t)-1, not -1, and (unsigned long)-1 is valid,
so, this is valid even if a bit strange. mqd_t is an opaque type for
the user anyway, so its actual type should not matter to you.

But in fact we do not even need a long type since what is returned
is a file descriptor, so, we could have typedef int mqd_t like
glibc.

-- 
					    Gilles.