Date: Mon, 03 Nov 2014 00:04:20 +0800 From: Julian Elischer <julian@freebsd.org> To: Rick Macklem <rmacklem@uoguelph.ca>, Ian Lepore <ian@FreeBSD.org> Cc: Freebsd hackers list <freebsd-hackers@freebsd.org> Subject: Re: how to kernel printf a int64_t? Message-ID: <54565604.2030208@freebsd.org> In-Reply-To: <1123726553.4004621.1414932491616.JavaMail.root@uoguelph.ca> References: <1123726553.4004621.1414932491616.JavaMail.root@uoguelph.ca>
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On 11/2/14, 8:48 PM, Rick Macklem wrote:
> Ian Lepore wrote:
>> On Sun, 2014-11-02 at 11:20 +0800, Julian Elischer wrote:
>>> On 11/2/14, 10:14 AM, Rick Macklem wrote:
>>>> Julian Elischer wrote:
>>>>> On 10/31/14, 1:09 PM, Tim Kientzle wrote:
>>>>>
>>>>>
>>>>> On Oct 30, 2014, at 2:01 PM, Rick Macklem <rmacklem@uoguelph.ca>
>>>>> wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I feel kinda dumb asking this, but...
>>>>> int64_t i;
>>>>>
>>>>> printf("%qd\n", (u_quad_t)i);
>>>>>
>>>>> works but looks dorky, to put it technically;-).
>>>>> Is there a better way to printf() a int64_t in the kernel? I
>>>>> often
>>>>> use the following to print large integers:
>>>>>
>>>>> printf(“%jd\n”, (intmax_t)i); the "cannonical' way is to
>>>>> use
>>>>> PRIu64 and friends, but some people seem to have a problem
>>>>> with
>>>>> doing that.
>>>>>
>>>> Ok, so now I need to ask another dumb question.
>>>> How do you do this in the kernel?
>>>> (I can see them defines in <machine/_inttypes.h>, but including
>>>> that
>>>> doesn't help, which isn't surprising since PRIu64 is in a
>>>> string
>>>> and won't be recognized as a macro.)
>>> you use it with string concatenation.
>>> like:
>>>
>>> printf (" this is a 64 it unsigned value: %" PRIu64 " and I
>>> just
>>> printed it\n", thingy64);
>>>
>>> After substitution the compiler sees
>>> " this is a 64 it unsigned value: %" "llu" " and I just printed
>>> it\n"
>>> which simplifies to:
>>> " this is a 64 it unsigned value: %llu and I just printed it\n"
>>>
>>> due to concatenation. (note I didn't actually look what PRIu64
>>> evaluates to)
>>>
>>>
>> Which is exactly the explanation for why "some people seem to have a
>> problem with doing that." "Some people" would be "anyone who thinks
>> it
>> should be possible to read code as well as write it." This may be
>> more
>> correct in some pedantic sense, but %j and a cast is more readable.
>>
> Yes, thanks. I'll admit to thinking exactly the same thing.
> I guess I'll use %j.
then your code could be wrong in some cases..
PRIu64 specifies that the value will always be 64 bits (unsigned) on
every architecture.
If that's NOT true then yes, use a type (e.g. %d) that varies here and
there.
If your value will ALWAYS be 64 but then PRIu64 describes what it is
much better than
%j, because you need to know what %j expects on every architecture your
code may ever run on.
In my own opinion, PRIu64 is much more readable than %j because the size
and expected signed/unsigned characterisitics are right there, where
%randomletter is exactly that.. completely random, requiring that the
reader go
consult a man page first before reading code for any given architecture.
>
> Thanks everyone for your help, rick
>
>> -- Ian
>>
>>>> Oh, and is intmax_t going to be int64_t on all arches?
>>>>
>>>> Thanks, rick
>>>>
>>>>> Tim
>>>>>
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>>>>
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>>
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>
>
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