Re: What is the right way to print a UINTN?

["Brian J. Johnson" <bjohnson@sgi.com>]

On 09/27/2016 11:47 AM, Andrew Fish wrote:
>
>> On Sep 27, 2016, at 9:03 AM, Cohen, Eugene <eugene@hp.com> wrote:
>>
>>> Printing UINTN with %x *or* with %d are equally bugs.
>>>
>>> For X64 / AARCH64 / IA64 builds, they are actual bugs (that happen to
>>> work most of the time).
>>
>> Feel free to file a Bugzilla on the extensive usage of this in
>> edk2 [ducking and running]. :)
>>
>>>> I'm envisioning having to create a slide in the future for UEFI
>>>> training about the proper use of UINTNs and describing "If you think
>>>> it may exceed 2^32-1 then upcast to UINT64, otherwise don't worry
>>>> about it" and it makes me squirm.
>>>
>>> It makes me squirm too. I think the slide should recommend the
>>> casting
>>> that I proposed. ;) "There is no conversion specifier dedicated to
>>> UINTN; the portable way to print it is to cast it to UINT64, then print
>>> it with %Lx."
>>
>> This is reasonable although I expect to get asked why a lot of the
>> other code doesn't adhere to this recommendation.
>>
>
> I think this is a historical artifact. The older version of %x in
> the EDK (and early edk2) implied UINTN. We hit an issue with C
> integer math resulting in an int and that seemed to bork some
> toolchains. That is when things changed from UINTN to int. I guess
> the cleanup was practical vs. pedantic.

Thanks for the historical context, Andrew.  It's interesting to hear,
if very unfortunate.

I've written code in the past which uses a #defined value for the
UINTN format character as a way to work around this issue without
casting everything to 64 bits.  Something like:

// Format string for a naturally-sized unsigned integer
#if defined (MDE_CPU_IA32)
#define UINTN_FMT  "0x%08x"
#elif defined (MDE_CPU_X64)
#define UINTN_FMT  "0x%016lx"
#elif ...
   ...
#endif

UINTN Val;
Val = Foo ();
DEBUG((DEBUG_INFO, "Value is " UINTN_FMT "\n", Val));


I guess it's a matter of opinion if that's preferable to adding casts;
in my particular situation, I had to print values with that particular
format string in a lot of places, so it was convenient to #define it
once.

>
> Thanks,
>
> Andrew Fish
>
>> Thanks,
>>
>> Eugene
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-- 

						Brian J. Johnson

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