I have a question related to setting a C++ member function as a callback function for C library's API. I searched the boost mailing list and Google, but I could not find a clear answer. The function I need to call is OpenSSL's CRYPTO_set_id_callback function. It accepts a function pointer as its parameter. The following code works fine: unsigned long IdCallBack( ) { return ( ( unsigned long )GetCurrentThreadId( ) ); } CRYPTO_set_id_callback( (unsigned long (*)())IdCallBack ); I have a C++ class and I want to set the call back function to be the member function of my class, I tried to use boost::bind: class Test { public: Test( unsigned long a ) : m_long( a ) { } virtual ~Test( ) { } unsigned long GetId() { return m_long; } void SetCallBack() { CRYPTO_set_id_callback( boost::bind( &Test::GetId, this ) ); } private: unsigned long m_long; }; I got the following error under VC++ 7.1: error C2664: 'CRYPTO_set_id_callback' : cannot convert parameter 1 from 'boost::_bi::bind_t<R,F,L>' to 'unsigned long (__cdecl *)(void)' with [ R=unsigned long, F=boost::_mfi::mf0<unsigned long,Test>, L=boost::_bi::list1<boost::_bi::list_av_1<Test *>::B1> ] No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called Is it possible to use boost::bind to bind a C++ member function as a callback function for C interface? Thank you