Function Pointer

[JanDeclercq]

Hey,

I have a header file with this line of code:

extern "C" void amqC_dataInit(const char *uri, const char *channel,int (*cb_MessageReceived)(const TRANSFERDATA_FULL * dataToSend,const char action),int useTopics,FILE * logfile);


In C I can use this code like this:

int receiveData(const TRANSFERDATA_FULL * sendData, const char action) {
	fprintf(stdout, "LSPI = %s", sendData->lsph);fflush(stdout);
	return 0;
}

In the main file i place this line:

amqC_dataInit("foo","test",&receiveData,1,stdout);


this compiles and works perfectly

In C++ I have this code:

Header file:

class Test {
	private:
		int messageReceived(const TRANSFERDATA_FULL * sendData, const char action);
	public:
		Test();
		virtual ~Test();
		bool initialize();
		bool stop();
	};

cpp file:

	Test::Test() {
	}

	Test::~Test() {
	}

	bool Test::initialize() {
		amqC_dataInit(this->m_ActiveMQUri.c_str(), this->m_ActiveMQUri.c_str(), &Test::messageReceived, 0, stdout);
		return true;
	}

	bool Test::stop() {
		return true;
	}

	int Test::messageReceived(const TRANSFERDATA_FULL * sendData, const char action) {

	}

This gives me the compile error:

error: cannot convert ‘int (hms::Test::*)(const TRANSFERDATA_FULL*, char)’ to ‘int (*)(const TRANSFERDATA_FULL*, char)’ for argument ‘3’ to ‘void amqC_dataInit(const char*, const char*, int (*)(const TRANSFERDATA_FULL*, char), int, FILE*)’
make: *** [src/Test.o] Error 1

The only difference I see is the hms::Test:: (The namespace and the class name).

Am I not seeing something, or is this just not possible?

Thankx in advance.
Jan

[webJose]

Not the best one @ function pointers here, but I think it should be Test::messageReceived instead of &Test::messageReceived.

But I think that is just one part of it. I believe you are trying to use a function pointer of a non-static function as a regular C pointer. I think this is not allowed. But again, I'm not the brightest fellow for function pointers.

[jsmith]

Yes to the second part. Pointers to member functions are different than pointers to free functions because of the implicit "this" pointer.

[S6k9GNh0]

The use of Boost.Bind or the upcoming std::bind can be used to bind member functions into a simple (non-)nullary function. They simplify what you're trying to do. I suggest you look it up. Please be warned though that the errors produced by bind are horrendous and takes patience. You may be better off simply creating a cleaner solution.

As to whether you should use Boost.Bind or std::bind, I'd use Boost.Bind for current portability sake.

[jsmith]

However, neither boost::bind nor std::bind will solve OP's problem. Once a C function pointer, always a C function pointer.

[S6k9GNh0]

I forgot to suggest boost::function.