Changing the OpenSSL API is not an option for me. Let's assume that the callback function accepts a void* parameter, can you show me an example that I can bind C++ member function to a C callback function? Thank you

I got the following error under VC++ 7.1:

error C2664: 'CRYPTO_set_id_callback' : cannot convert parameter 1 from 'boost::_bi::bind_t' to 'unsigned long (__cdecl *)(void)' with [ R=unsigned long, F=boost::_mfi::mf0, L=boost::_bi::list1::B1> ] No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called

It doesn't even take in void *???? Maybe the fact that it doesn't take in state means something. You should look up that specific callback in the openssl documentation

Is it possible to use boost::bind to bind a C++ member function as a callback function for C interface?

Its easy given that said C interface allows the user to pass in "other data" a la void *.