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Re: [Qemu-devel] [PATCH 1/3] qmp-event: Avoid qobject_from_jsonf("%"PRId

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH 1/3] qmp-event: Avoid qobject_from_jsonf("%"PRId64)
Date: Wed, 23 Nov 2016 08:04:20 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 11/23/2016 07:56 AM, Eric Blake wrote:
>> In my opinion, the code becomes less readable.
>> We want to convert struct timeval members tv_sec (of type time_t) and
>> tv_usec (of type suseconds_t) here.  Since qobject_from_jsonf() lacks
>> conversion specifiers for time_t and suseconds_t,

Note that printf likewise lacks such conversions, so...

>> we convert to int64_t
>> first, then use PRId64.

...some conversion is necessary no matter what, even if it is to 'long
long' instead of 'int64_t'.  Also, our choice of using -1 as the
sentinel for failures is difficult to portably code if we don't know if
time_t is signed or unsigned (if it is a 32-bit unsigned value, widening
it to long long won't give us our desired value), so it is not as simple
as doing tv.tv_sec = -1; we still need a conditional or temporary.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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