Even if it requires manual input. Is there any good-enough option available?
                +2 
                A: 
                
                
              I don't know anything about this site, but a little googling found this.
                  itsmatt
                   2008-10-01 23:53:57
                
              I played around with this very briefly... I suppose it might save you a little time, but I'd probably do it manually myself anyhow.
                  itsmatt
                   2008-10-01 23:56:19
                I found that site but I do not think it is open source.
                  antonio
                   2008-10-01 23:56:36
                Yeah, and I'd be reluctant to put any of my production code on it.
                  itsmatt
                   2008-10-01 23:58:30
                Still a pretty useful tool to quickly evaluate something you may be thinking of converting
                  mattlant
                   2008-10-02 04:17:43
                
                
                A: 
                
                
              
            If it was in managed C++ or C++/CLI, you could compile it and then disassemble the assembly into C# using a tool like Reflector. Of course, that's not open source but maybe you can find an open source Reflector-style tool?
If it's native C++, that's much more difficult.
                  Jeff Yates
                   2008-10-02 04:09:26