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Subject:	Re: bug in lrint [was: FW: Printing long int in C program under cygwin64]
To:	cygwin AT cygwin DOT com
References:	<d252aaae-b298-6fc8-7e5b-8d8be9f27f21 AT redhat DOT com> <592618e3 DOT 08179d0a DOT 27b5e DOT 4630 AT mx DOT google DOT com>
From:	Eric Blake <eblake AT redhat DOT com>
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Date:	Thu, 25 May 2017 13:17:30 -0500
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From: Eric Blake <eblake AT redhat DOT com>
To: cygwin AT cygwin DOT com
Message-ID: <f38a6091-a097-baec-5f9b-927070cc4d5f AT redhat DOT com>
Subject: Re: bug in lrint [was: FW: Printing long int in C program under
 cygwin64]
References: <d252aaae-b298-6fc8-7e5b-8d8be9f27f21 AT redhat DOT com>
 <592618e3 DOT 08179d0a DOT 27b5e DOT 4630 AT mx DOT google DOT com>
In-Reply-To: <592618e3 DOT 08179d0a DOT 27b5e DOT 4630 AT mx DOT google DOT com>


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On 05/24/2017 06:36 PM, Steven Penny wrote:
> On Wed, 24 May 2017 07:33:27, Eric Blake wrote:
>> Buggy.  size_t should be printed with %zi, not %i (since size_t and int
>> are not necessarily the same type).
>=20
> Aren=E2=80=99t both wrong? By definition %i is a signed integer, and size=
_t is
> unsigned.
> So %zu

Correct.  Newer gcc's -Wformat-signedness will flag the discrepency.

> or %llu would be more correct:

NO. Do NOT use %llu with size_t, because it is not portable to 32-bit
platforms.  That's WHY %zu exists.

> They all seem to do the job though:

Yes. On all modern platforms, you can freely mix signed and unsigned
integers and get correct (when the number is positive and does not
exceed the signed maximum) or at least sane results (2s complement
counterpart for all other values) regardless of which direction you mess
with incorrect signedness.  However, such behavior is technically not
required by the C standard, which is why gcc added -Wformat-signedness.

--=20
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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