[cfe-dev] printf: invalid conversion specifier: 'I' when using "I64d" on Windows

[Ruben Van Boxem]

Hi,

Windows' msvcrt.dll has weird printf format strings that aren't used
anywhere else.

For example this code with Clang 3.1 on MinGW-w64 using GCC 4.6.3 libstdc++
headers:
#define __STDC_FORMAT_MACROS
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <fstream>
int main(int argc,char **argv)
{
   uint64_t val=1234567890;
   printf("%" PRId64"\n",val);
   exit(0);
}

produces this warning:
M:\Development\x64\test>clang++ -std=c++11 test.cpp -c -Wall
test.cpp:11:15: warning: invalid conversion specifier 'I'
      [-Wformat-invalid-specifier]
   printf("%" PRId64"\n",val);
           ~~~^
M:/Development/mingw64/bin/../lib/clang/3.1/../../../x86_64-w64-mingw32/include\inttypes.h:42:17:
note:
      expanded from macro 'PRId64'
#define PRId64 "I64d"
                ^
1 warning generated.

The "I64d" form is the "correct" msvcrt printf format string for this case,
and the define in the mingw-w64 header inttypes.h is used to make the code
correct and thus work around the msvcrt limitations.

Clang (and don't worry, GCC too) warns on this use, while it really
shouldn't, as this is correct on Windows. I understand from a MinGW-w64 dev
that they annotate their printf prototype correctly, but the compiler's
builtin definition conflicts with this, and hence the warning. So I think
the right solution here is to allow the MS printf format strings as well.
This should work for both Visual Studio based and MinGW-w64 based Clang.

I was looking through the code, and found:
http://llvm.org/svn/llvm-project/cfe/trunk/lib/Analysis/PrintfFormatString.cpp
where I think the format string is handled, because printf is defined in
http://llvm.org/svn/llvm-project/cfe/trunk/include/clang/Basic/Builtins.def
as a builtin.
The warning is thrown from
http://llvm.org/svn/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp
as "diag::warn_format_invalid_conversion" I *think*.

Am I right that there should be a modification to PrintfFormatString.cpp
(and maybe ScanfFormatString.cpp as well?) to allow the MS specific format
specifiers as defined here
http://msdn.microsoft.com/en-us/library/56e442dc.aspx ?

I would prepare a patch, but I have no idea if the above is correct and
what exactly (and how) I'd have to add this.

Therefore: any help is much appreciated!

Thanks,

Ruben

PS: please reply to my email directly as well, I'm not subscribed to cfe-dev
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