Re: [Quickfix-developers] Confused by possible bug in Utility.cpp / thread_spawn

[K. F. <kfr...@gm...>]

Hi Mike!

On Tue, Jan 15, 2013 at 1:10 PM, Mike Gatny <mg...@co...> wrote:
> It works with the VS compiler (32-bit, anyway).  Can you post the actual
> error message that mingw-w64 is giving you?

Yes, I'd be happy to post the mingw-w64 error message.

But before I do, I would like to check whether the code looks to you
like it has an error, or whether I'm missing something simple about
relatively basic c++.  (Again the issue is that I see a
pointer-to-pointer-to-function (double pointer) being passed, while a
pointer-to-function (single pointer) is expected.)  Does this look
like an error to you?

Anyway, here's the mingw-w64 error message:

   Utility.cpp: In function 'bool FIX::thread_spawn(unsigned int
(*)(void*), void*, FIX::thread_id&)':
   Utility.cpp:510:56: error: cannot convert 'unsigned int
(**)(void*)' to 'unsigned int (*)(void*)' for argument '3' to
'uintptr_t _beginthreadex(void*, unsigned int, unsigned int
(*)(void*), void*, unsigned int, unsigned int*)'

In a way, I'm not surprised that you don't see the issue with visual
studio, because if you did, you would have changed the code.  So
I wonder whether visual studio might be doing something wrong or
non-standard here.  (I'm not aware of anything, but I'm not that
expert with visual studio.)  Or maybe g++ / mingw-w64 is doing
something non-standard.  But again, when I parse the code by
eye, I come up with a type mismatch.

(Just to note, the linux builds with g++ wouldn't have caught this
because this is in the windows-specific part of the threading code.
I verified -- at least to my eye -- that the analogous posix-threading
part of the code doesn't have this issue.)

By the way, if I "fix" the code by changing

   result = _beginthreadex( NULL, 0, &func, var, 0, &id );

to

   result = _beginthreadex( NULL, 0, func, var, 0, &id );

(that is, removing what appears to be the extra '&' from "&func")
the code compiles under mingw-w64.  I don't know whether the
code runs correctly because I haven't been able to compile all
of the rest of the code.  But I would be worried about just making
this change blindly because there is something going on that I
don't understand.


Thanks for helping me sort this out.


K. Frank