Re: [patch] Use inttypes macros for size_t format string

[Tilo Eckert <tilo.eckert@xxxxxxx>]

Am 23.01.2020 um 10:00 schrieb Andreas Schneider:
> On Wednesday, 22 January 2020 17:40:04 CET Tilo Eckert wrote:
>> Am 22.01.2020 um 13:56 schrieb g4-lisz@xxxxxxxxxxxx:
>>> For Windows I can find documentation of "z" as supported spezifier:
>>> https://docs.microsoft.com/en-us/cpp/c-runtime-library/format-specificatio
>>> n-syntax-printf-and-wprintf-functions?view=vs-2019#size-prefixes-for-print
>>> f-and-wprintf-format-type-specifiers
>>>
>>> But not sure since when this is supported.
>>
>> Apparently, %zu is supported since VS 2015 (or 2013?), %Iu is the older
>> MS-specific alternative. Support for ANSI C99 still seems not to be 100%
>> complete in VS.
>>
>>> But anway: What is the advantage of using typecasts instead of a format
>>> spezifier macro (see my patch)? You still have to use OS specific type
>>> casts. Or I'm understanding this wrong?
>>
>> There is no printf format specifier macro for size_t in standard
>> headers. The PRIdS macro in priv.h defines a format specifier for
>> printing a ssize_t. We would need a PRIuS macro (`Iu` on Windows, `zu`
>> everywhere else) as you suggested in an earlier email because size_t is
>> unsigned. However, I'm not 100% certain whether this works in all build
>> environments. If you get this macro wrong, not all compilers will warn
>> you about a bad format string.
>>
>> A safe, headache-free, C89 compatible, but not as pretty alternative
>> that will not break in compiler environments of the last 20+ years:
>> printf("%llu", (long long unsigned) size)
> 
> I would prefer to go with:
> 
> -Dsnprintf=__mingw_snprintf -Dvsnprintf=__mingw_vsnprintf
> 
> 
> The question is if we should document how to do it with mingw and suggest a 
> toolchain file having this set, or if we add this to our cmake or priv.h in 
> case of MinGW ...

This is not a MinGW problem, but a general Windows one as I already
tried to explain. Format specifier %zu is not supported in VS versions
older than 5 years because MS didn't bother to make their printf
implementation comply to C99 for a long time. Hence, we should use
MS-proprietary %Iu on Windows or avoid using %z at all to make format
strings compatible with MinGW and VS.

Regards,
Tilo