[boost] [Regex] Calling convention for _MANAGED code still somewhat broken when mixing native and managed projects

Subject: [boost] [Regex] Calling convention for _MANAGED code still somewhat broken when mixing native and managed projects
From: Martin B. (0xCDCDCDCD_at_[hidden])
Date: 2011-12-02 00:59:17

Hi there!

Background
----------

The header boost/regex/config.hpp currently contains the following code:

        #if defined(BOOST_MSVC) && (BOOST_MSVC >= 1200) && defined(_MSC_EXTENSIONS)
        #if defined(_DEBUG) || defined(__MSVC_RUNTIME_CHECKS) || defined(_MANAGED)
        #  define BOOST_REGEX_CALL __cdecl
        #else
        #  define BOOST_REGEX_CALL __fastcall
        #endif
        #  define BOOST_REGEX_CCALL __cdecl
        #endif

the `|| defined(_MANAGED)` was added in 2006 (SVN history) to cater for 
the fact that __fastcall does not work on managed C++/CLI (/clr 
compiled) projects.

See, e.g. this: http://lists.boost.org/boost-users/2004/12/9203.php

Problem
-------

This is really quite suboptimal, as with the solution as posted above, 
you need *a separate* lib/dll for managed-C++ and native-C++ Projects.

Especially for the DLL, this is a non-solution, as I can only have one 
DLL for projects/modules that are used in the same application.

_MANAGED is a define set by the VC compiler if the /clr switch is 
present, therefore it is actually never set when compiling the boost 
libraries. Of course you can set it via `define=_MANAGED` and you can 
then use these generated libraries from a C++/CLI project. (Which I have 
done: ... `define=_MANAGED` ... --with-regex ...)

BUT: You can now *not* use these libraries from a non-managed ("native") 
C++ project as that, obviously, doesn't have _MANAGED set, and unlike 
with the boost build, I don't think it's feasible to define this 
wholesale for a native project. (And anyways, I'm rather hesitant to 
define this myself.)

Obviously, I could just edit regex/config.hpp, but that is a maintenance 
nightmare of its own here.

Solution
--------

I *think* what really would be needed would be a define that the user 
could specify, something like this:

        #if defined(_DEBUG) || ... || defined(BOOST_REGEX_NO_FASTCALL)
        #  define BOOST_REGEX_CALL __cdecl
        ...

(I have attached a patch, hope this works.)

Would this make sense?

To add a short rationale: We use C++/CLI projects as bridges between 
managed and native modules of our application. In the C++ part, we use 
boost regexes, and sometimes it would make sense to reuse some native 
code in a C++/CLI bridge module. If this native code uses Boost.Regex, 
this doesn't work currently, as the native code file will also be 
compiled with /clr, and then we have a calling convention mismatch and 
can't use our boost-regex-dll.

cheers,
Martin