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Re: cygwin x86_64: mingw64-g++ 6.4.0 (both i686 and x86_64) issue (bug?) with reinterpret_cast




Hi Csaba,

Ok, then the issue are "my" lines of code and the error messages from g++ were not completely clear (and they was confusing me a little bit)...
But I'm still not sure the issue is not in Cygwin package. I mean, my test code was a very simplified (too much simplified) excerpt from squid source code and, there, the link with header file from cygwin package is more clear.
Then, let me post another test file where this link is more clear.

Now the failure is as follow (g++ -std=gnu++11 -c -Wall -pedantic -Wextra test.cpp)

In file included from /usr/i686-w64-mingw32/sys-root/mingw/include/winbase.h:19:0,
                 from /usr/i686-w64-mingw32/sys-root/mingw/include/windows.h:70,
                 from test.cpp:1:
test.cpp:6:45: error: reinterpret_cast from integer to pointer
     static constexpr HANDLE InvalidHandle = INVALID_HANDLE_VALUE;
                                             ^

The issue is now within the macro definition of INVALID_HANDLE_VALUE in file handleapi.h (which could be, from i686-w64-mingw32, x86_64-w64-mingw32 or w32api)

Now I'm wondering what is really wrong:
	does the definition of INVALID_HANDLE_VALUE need to be rewritten in order to be compatible with the "static constexpr" line
	or
	does "my" line of code has to be rewritten in order to be compatible with the INVALID_HANDLE_VALUE definition?

In the latest case, any suggestion will be very welcome...

Paolo.

> Hi Paolo,
> 
> On Mon, Oct 23, 2017 at 4:47 PM, Paolo ZAMBOTTI <paolo.zambotti@xxxxxx> wrote:
> > Hello,
> >
> > I'm having some issues while compiling C++ code with mingw64 c++ compiler (6.4.0) distributed within Cygwin packages.
> > I can guess the issue I'm going to report is not strictly related to Cygwin distribution but I cannot test other mingw64 distributions so let me start reporting the issue here...
> > Once said that, I'm open to any suggestions for better reporting place...
> >
> > I'm not an expert in C and even less in C++ so I hope to not generate stupid noise... but the same code was compiling fine with previous version (5.4) ...
> 
> Note that compilers tend to become more picky with time. The fact that
> this code was compiling fine with GCC 5.4 may well be a bug in GCC 5.4
> 
> $ gcc-630 -std=gnu++11 -c -Wall -pedantic -Wextra fail.cpp
> fail.cpp: In function 'int main(int, char**)':
> fail.cpp:10:34: error: reinterpret_cast from integer to pointer
>    static constexpr void* test1 = (void*)(-1LL);
>                                   ^~~~~~~~~~~~~
> fail.cpp:11:34: error: reinterpret_cast from integer to pointer
>    static constexpr void* test2 = (void*)(-1L);
>                                   ^~~~~~~~~~~~
> 
> $ gcc-7 -std=gnu++11 -c -Wall -pedantic -Wextra fail.cpp
> gcc-7    gcc-710
> csabaraduly@HU-GD-36813:/tmp
> $ gcc-7 -std=gnu++11 -c -Wall -pedantic -Wextra fail.cpp
> fail.cpp: In function 'int main(int, char**)':
> fail.cpp:10:34: error: 'reinterpret_cast<void*>(-1)' is not a constant
> expression
>    static constexpr void* test1 = (void*)(-1LL);
>                                   ^~~~~~~~~~~~~
> fail.cpp:11:34: error: 'reinterpret_cast<void*>(-1)' is not a constant
> expression
>    static constexpr void* test2 = (void*)(-1L);
>                                   ^~~~~~~~~~~~
> 
> $ gcc-8 -std=gnu++11 -c -Wall -pedantic -Wextra fail.cpp
> fail.cpp: In function 'int main(int, char**)':
> fail.cpp:10:34: error: reinterpret_cast from integer to pointer
>    static constexpr void* test1 = (void*)(-1LL);
>                                   ^~~~~~~~~~~~~
> fail.cpp:11:34: error: reinterpret_cast from integer to pointer
>    static constexpr void* test2 = (void*)(-1L);
>                                   ^~~~~~~~~~~~
> 
> $ clang++ -std=gnu++11 -c -Wall -pedantic -Wextra fail.cpp
> fail.cpp:10:26: error: constexpr variable 'test1' must be initialized
> by a constant expression
>   static constexpr void* test1 = (void*)(-1LL);
>                          ^       ~~~~~~~~~~~~~
> fail.cpp:10:34: note: cast that performs the conversions of a
> reinterpret_cast is not allowed in a constant expression
>   static constexpr void* test1 = (void*)(-1LL);
>                                  ^
> fail.cpp:11:26: error: constexpr variable 'test2' must be initialized
> by a constant expression
>   static constexpr void* test2 = (void*)(-1L);
>                          ^       ~~~~~~~~~~~~
> fail.cpp:11:34: note: cast that performs the conversions of a
> reinterpret_cast is not allowed in a constant expression
>   static constexpr void* test2 = (void*)(-1L);
>                                  ^
> 
> I think clang explains it best.
> Note: these were Linux compilers, but your question is not
> Cygwin-specific (and including windows.h is unnecessary).
> 
> Csaba
> -- 
> GCS a+ e++ d- C++ ULS$ L+$ !E- W++ P+++$ w++$ tv+ b++ DI D++ 5++
> The Tao of math: The numbers you can count are not the real numbers.
> Life is complex, with real and imaginary parts.
> "Ok, it boots. Which means it must be bug-free and perfect. " -- Linus Torvalds
> "People disagree with me. I just ignore them." -- Linus Torvalds
#include <windows.h>
#include <stdio.h>

class test {
  private:
    static constexpr HANDLE InvalidHandle = INVALID_HANDLE_VALUE;
    
  public:
    HANDLE get_InvHahndle(void) {
      return InvalidHandle;
    }
};
  

int main (__attribute__((unused)) int argc, __attribute__((unused)) char **argv) {
  test fail;
  
  printf("%llx\n", (long long)(fail.get_InvHahndle()));

return 0;

}
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