#846 wprintf, swprintf etc. don't check format specifiers vs. arguments on compile

[David Macek]

Source:

#define __USE_MINGW_ANSI_STDIO 1
#define _UNICODE
#include <stdio.h>
#include <wchar.h>

int wmain(int argc, wchar_t *argv[]) {
    wprintf(L"argc=%d argv[0]=%s", argc, argv[0]);
    return 0;
}

Observed behavior:

> gcc -municode -std=c11 -Wall -Wextra -Werror -pedantic example.c -o example.exe
> example.exe
argc=1 argv[0]=e

Expected behavior:

GCC emits an error during compilation.

Version:

> gcc -v
 Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=D:/msys64/mingw64/lib/gcc/x86_64-w64-mingw32/10.1.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../gcc-10.1.0/configure --prefix=/mingw64 --with-local-prefix=/mingw64/local --build=x86_64-w64-mingw32 --host=x86_64-w64-mingw32 --target=x86_64-w64-mingw32 --with-native-system-header-dir=/mingw64/x86_64-w64-mingw32/include --libexecdir=/mingw64/lib --enable-bootstrap --with-arch=x86-64 --with-tune=generic --enable-languages=c,lto,c++,fortran,ada,objc,obj-c++ --enable-shared --enable-static --enable-libatomic --enable-threads=posix --enable-graphite --enable-fully-dynamic-string --enable-libstdcxx-filesystem-ts=yes --enable-libstdcxx-time=yes --disable-libstdcxx-pch --disable-libstdcxx-debug --disable-isl-version-check --enable-lto --enable-libgomp --disable-multilib --enable-checking=release --disable-rpath --disable-win32-registry --disable-nls --disable-werror --disable-symvers --disable-plugin --with-libiconv --with-system-zlib --with-gmp=/mingw64 --with-mpfr=/mingw64 --with-mpc=/mingw64 --with-isl=/mingw64 --with-pkgversion='Rev3, Built by MSYS2 project' --with-bugurl=https://sourceforge.net/projects/msys2 --with-gnu-as --with-gnu-ld
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.1.0 (Rev3, Built by MSYS2 project)

[Kai Tietz]

Hello,

Well, I would not say that diagnostic is wrong here. As for
wide-character routine '%s' still represents an array of characters,
means here an array of wchar_t. For futher reading please see
https://man7.org/linux/man-pages/man3/wprintf.3.html

Regards,
Kai

Am Fr., 19. Juni 2020 um 10:48 Uhr schrieb David Macek
elieux@users.sourceforge.net:

---

[bugs:#846] wprintf, swprintf etc. don't check format specifiers vs. arguments on compile

Status: open
Group: v1.0 (example)
Created: Fri Jun 19, 2020 08:48 AM UTC by David Macek
Last Updated: Fri Jun 19, 2020 08:48 AM UTC
Owner: nobody

Source:

define __USE_MINGW_ANSI_STDIO 1

define _UNICODE

include <stdio.h></stdio.h>

include <wchar.h></wchar.h>

int wmain(int argc, wchar_t *argv[]) {
wprintf(L"argc=%d argv[0]=%s", argc, argv[0]);
return 0;
}

Observed behavior:

gcc -municode -std=c11 -Wall -Wextra -Werror -pedantic example.c -o example.exe
example.exe
argc=1 argv[0]=e

Expected behavior:

GCC emits an error during compilation.

Version:

gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=D:/msys64/mingw64/lib/gcc/x86_64-w64-mingw32/10.1.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../gcc-10.1.0/configure --prefix=/mingw64 --with-local-prefix=/mingw64/local --build=x86_64-w64-mingw32 --host=x86_64-w64-mingw32 --target=x86_64-w64-mingw32 --with-native-system-header-dir=/mingw64/x86_64-w64-mingw32/include --libexecdir=/mingw64/lib --enable-bootstrap --with-arch=x86-64 --with-tune=generic --enable-languages=c,lto,c++,fortran,ada,objc,obj-c++ --enable-shared --enable-static --enable-libatomic --enable-threads=posix --enable-graphite --enable-fully-dynamic-string --enable-libstdcxx-filesystem-ts=yes --enable-libstdcxx-time=yes --disable-libstdcxx-pch --disable-libstdcxx-debug --disable-isl-version-check --enable-lto --enable-libgomp --disable-multilib --enable-checking=release --disable-rpath --disable-win32-registry --disable-nls --disable-werror --disable-symvers --disable-plugin --with-libiconv --with-system-zlib --with-gmp=/mingw64 --with-mpfr=/mingw64 --with-mpc=/mingw64 --with-isl=/mingw64 --with-pkgversion='Rev3, Built by MSYS2 project' --with-bugurl=https://sourceforge.net/projects/msys2 --with-gnu-as --with-gnu-ld
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.1.0 (Rev3, Built by MSYS2 project)

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[David Macek]

The diagnostic reports an error in the reverse situation, why should it not report both?

#define __USE_MINGW_ANSI_STDIO 1
#include <stdio.h>

int main(int argc, char *argv[]) {
    printf("argc=%d argv[0]=%ls", argc, argv[0]);

    return 0;
}

> gcc -std=c11 -Wall -Wextra -Werror -pedantic narrow.c
a.c: In function 'main':
a.c:7:28: error: format '%ls' expects argument of type 'wchar_t *', but argument 3 has type 'char *' [-Werror=format=]
    7 |  printf("argc=%d argv[0]=%ls", argc, argv[0]);
      |                          ~~^         ~~~~~~~
      |                            |             |
      |                            |             char *
      |                            short unsigned int *
      |                          %s
cc1.exe: all warnings being treated as errors

[David Macek]

I think I may have missed the point here with the example. Let me try again:

#include <stdio.h>

int main(int argc, char *argv[]) {
    wprintf(L"argc=%f argv[0]=%d", argc, argv[0]);
    return 0;
}

> gcc -std=c11 -Wall -Wextra -Werror -pedantic example.c -o example.exe
> example.exe
argc=0.000000 argv[0]=11408304

This surely deserves some warnings. :)