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

["Cohen, Eugene" <eugene@hp.com>]

Laszlo,
 
> I print INTN / UINTN values with:
> - casting them unconditionally to INT64 / UINT64,
> - printing the converted values with the matching conversion
> specifiers,
> such as %Ld (for INT64) and %Lu or %Lx (for UINT64).
> 
> This solution requires a bit more typing, and it is a bit pessimistic
> for 32-bit builds. On the positive side, it is robust / portable, and
> completely valid C.
> 
> It is inspired by the standard C types intmax_t / uintmax_t. If you
> write portable C code and want to print a value of some integer type,
> where the spec only states "signed" or "unsigned integer type", but
> the
> actual type is either implementation defined or unspecified,
> converting
> the value to intmax_t / uintmax_t, and then printing it with %jd vs. %ju
> / %jx, is safe.

Thanks - this makes sense.  If this methodology is consistent with standard C then perhaps it's the best compromise even if it's messy to read.

>From a consistency perspective I see a lot of variation in usage - often UINTNs are printed with %x / %d (technically it should be %u but this is a common error - just compare the number of occurrences of %u in MdeModulePkg versus %d).  This means that the caller is expecting that the value will never exceed 2^32-1 on 64-bit systems since we are doing 64-bit to 32-bit truncation through the cast in the VA_ARG macro.  I'm concerned that this requires the developer to know the constraints on the value in all circumstances which seems dubious - after all that's why we have types in the first place, so the tools can help us do the right thing.

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.

Eugene