# Coding Ruby Extension with C++ on Win32 **URL:** \ **Category:** Ruby\ **Created:** [January 28, 2008, 8:53am UTC](https://www.ruby-forum.com/t/coding-ruby-extension-with-c-on-win32/127322 "2008-01-28T08:53:08Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 28, 2008, 8:53am UTC](https://www.ruby-forum.com/t/coding-ruby-extension-with-c-on-win32/127322/1 "2008-01-28T08:53:08Z")
Here are some hurdles that I overcame when coding a Ruby Extension in C++ on Win32. Feel free to add to this or to comment. I hope it will help someone someday. (If you ask WHY?, my answer is: I’m very comfy with STL). 1. For Win32, mkmf generates makefiles for Visual Studio. In other words, “make” won’t work for you on Win32, you have to type “nmake”. I used VC6. And to use C++, the files you compile must be named “.cpp”, not “.c” so that they are compiled as c++ files instead of c files. Perhaps .cc extension works, I didn’t try. 2. Your static functions cannot be passed down to rb\_define\_method, rb\_define\_global\_function etc. The solution is not obvious. My first thought, extern “C”, \_\_cdecl/\_\_stdcall etc, does not do _anything_ to solve it. You have to do the following (found somewhere on net): // first a typedef typedef VALUE (\*HOOK)(…); // then do a reinterpret\_cast: rb\_define\_method(rb\_cYadaYada, “initialize”, reinterpret\_cast(yadayada\_initialize), 2); 1. Destructors in the functions are not called if ruby long jumps out! This happens when you raise an exception. Here is an example using the classical Lock-A-Mutex when the object is created, and Unlock-A-Mutex when the destructor is called: Lock my\_lock(mutex); connected = rb\_iv\_get(self, “@connected”); if(connected != Qtrue) { rb\_raise(rb\_eRuntimeError, YadaYada is not connected"); } When the exception is raised, the destructor of my\_lock WILL NOT BE CALLED so the Mutex is not unlocked. Nasty! 1. You have to #include before \. Otherwise you will get a lot of compile errors when #include:ing . This might apply to other include files, but it seemed not to apply to and . Cheers/D ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [January 28, 2008, 4:40pm UTC](https://www.ruby-forum.com/t/coding-ruby-extension-with-c-on-win32/127322/2 "2008-01-28T16:40:43Z")
On Mon, 28 Jan 2008 02:50:39 -0500, daniel Ã¥kerud wrote: > not “.c” so that they are compiled as c++ files instead of c files. > rb\_define\_method(rb\_cYadaYada, “initialize”, > > other include files, but it seemed not to apply to and . > > Cheers/D Try writing the whole OO interface in C++, and letting SWIG do the mapping into ruby for you. SWIG knows (with appropriate includes) about std::vector (which maps to Array) and std::string (which maps to String). –Ken ---
**Author:** ![daniel\_SSSSkerud](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/8e8cbc/32.png) [@daniel\_SSSSkerud](https://www.ruby-forum.com/u/daniel_SSSSkerud)\ **Post date:** [February 21, 2008, 3:45pm UTC](https://www.ruby-forum.com/t/coding-ruby-extension-with-c-on-win32/127322/3 "2008-02-21T15:45:51Z")
On Mon, Jan 28, 2008 at 04:50:39PM +0900, daniel ?kerud wrote: > // first a typedef > typedef VALUE (\*HOOK)(…); > // then do a reinterpret\_cast: > rb\_define\_method(rb\_cYadaYada, “initialize”, > reinterpret\_cast(yadayada\_initialize), 2); The problem is not that the methods are static; it’s that they don’t have the same signature as the rb\_define\_method function expects. You can cast to the right type using the RUBY\_METHOD\_FUNC() macro (this is what Rice does - see [http://rice.rubyforge.org](http://rice.rubyforge.org) - though it doesn’t work with a compiler as old as VC6). Some compilers also check the calling convention (e.g. comeau). Unfortunately, C++ provides no mechanism to specify both the calling convention _and_ the linkage, so if your compiler uses a different calling convention for C and C++ code, you _have_ to make your wrapper functions extern “C” (which is a nuisance, since it means it’s impossible to have internal linkage and C calling convention on such compilers). > 1. Destructors in the functions are not called if ruby long jumps out! This > happens when you raise an exception. IIRC the C++ standard does not specify what happens if you longjmp over code with objects on the stack that have destructors with non-trivial behavior. In other words, your destructor might get called, or it might not. The solution here is to use rb\_protect whenever you call into Ruby code. This is what Rice does under the hood. There’s a similar problem with allowing C++ exceptions to escape into Ruby-land; on most compilers I’ve used, this causes std::terminate to get called. > 1. You have to #include before \. Otherwise you will get a > lot of compile errors when #include:ing . This might apply to other > include files, but it seemed not to apply to and . I’ve not experienced this problem. What kinds of errors do you get? Paul