Lefteris Lefteris - 1 year ago 224
C Question

printf and %llx in GCC under Windows 64x

I am trying to get rid of a bogus warning in my program. Under windows 64 (under linux there is no such warning) this statement:


generates the following warning:

warning: unknown conversion type character 'l' in format [-Wformat]|

The output appears to be correct and the warning should not be there. The most relevant gcc related post I can find is this bug report back from 2008 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37768

If I understand correctly according to that, this warning stems from the fact that under the hood gcc calls MSVC printf which is not C99 compliant and can't understand the unsigned long long format in printf. From the same page the suggested solution is to use something called gnu_printf. I tried to google that but I did not find a header to include.

So the question is how should this be handled in order to be portable? I just want to get rid of the warning in a correct and non-sloppy way.

EDIT: For those looking at the question in the future, thanks to the link provided by the answerer the portable answer would be to use the header file inttypes.h.

Here is more information about it:

And the correct way to call printf would be with:


Answer Source

As I'm guessing you probably already know, from http://comments.gmane.org/gmane.comp.gnu.mingw.w64.general/4670 (note: dead link; see the Internet Archive's copy),

the issue is that formatter-width specifier %ll isn't supported for all msvcrt-DLL versions, therefore gcc warns about its use. The variant for specifying 64-bit integer-scalar-width in formatter for msvcrt in a backward-compatible way is by using %I64.

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