[Originally sent to Cygwin mailing list]
When printf/scanf functions from MinGW runtime are selected via
__USE_MINGW_ANSI_STDIO, then format string checking is broken. This only
affects the C++ compiler:
$ cygcheck -f /usr/bin/i686-w64-mingw32-g++
mingw64-i686-gcc-g++-4.5.3-4
$ cat testfmt.c
#define __USE_MINGW_ANSI_STDIO 1
#include <stdio.h>
void myprintf(const char *, ...)
__attribute__((format(gnu_printf,1,2)));
int main()
{
long long x = 42;
printf("%lld\n", x); // C++: Bogus warning
myprintf("%lld\n", x); // No warning (OK)
printf("%I64d\n", x); // Warning (OK)
return 0;
}
$ i686-w64-mingw32-gcc -Wformat -c testfmt.c
testfmt.c: In function 'main':
testfmt.c:12:3: warning: format '%I64d' expects type 'int', but argument
2 has type 'long long int'
$ i686-w64-mingw32-g++ -Wformat -c testfmt.c
testfmt.c: In function 'int main()':
testfmt.c:10:21: warning: unknown conversion type character 'l' in format
testfmt.c:10:21: warning: too many arguments for format
testfmt.c:12:22: warning: format '%I64d' expects type 'int', but
argument 2 has type 'long long int'
Interestingly the bogus warning only occurs for standard functions like
printf(). These are replaced by inline functions in MinGW stdio.h if
__USE_MINGW_ANSI_STDIO is set. Probably a subtle bug in the handling of
functions known by the compiler.
Downgrading to previous version fixes the problem:
$ cygcheck -f /usr/bin/i686-w64-mingw32-g++
mingw64-i686-gcc-g++-4.5.3-3
$ i686-w64-mingw32-g++ -Wformat -c testfmt.c
testfmt.c: In function 'int main()':
testfmt.c:12:22: warning: format '%I64d' expects type 'int', but
argument 2 has type 'long long int'
Another observation: Include files from C++ standard library (e.g.
<string>) now silently set __USE_MINGW_ANSI_STDIO:
/usr/lib/gcc/i686-w64-mingw32/4.5.3/include/c++/i686-w64-mingw32/bits/os_defines.h:
...
#undef __USE_MINGW_ANSI_STDIO
#define __USE_MINGW_ANSI_STDIO 1
Is this done to ensure that iostream templates use the correct
FILE/stdio version?
(This was also not present in previous version 4.5.3-3).
Christian
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