returning a pointer to a function

[DNA7433]

i have a templated class with this template header

template<class InputType, class ReturnType, class ParamType1, class ParamType2>

and a variable declared as such

ReturnType (*m_pFunc)(ParamType1, ParamType2);

a function prototype

ReturnType (*)(ParamType1, ParamType2) GetFuncPtr(void);

and the function body defined as follows

template<class InputType, class ReturnType, class ParamType1, class ParamType2>
ReturnType (*)(ParamType1, ParamType2) CMenuItem<InputType, ReturnType, ParamType1, ParamType2>::GetFuncPtr(void)
{}

it tells me syntax error: ')' in the function prototype
and unexpected tokens preceding ';'
and then some more errors that are created because of this

so what am i doing wrong? it all looks like it should logically work?

[CornedBee]

What compiler do you use? MSVC++6 has some problems with templates.
Although this code should work, I see no error.
Best thing is to use a typedef inside the class:

typedef ReturnType (*CLASSCALLBACK)(ParamType1, ParamType2);
CLASSCALLBACK m_pFunc;
CLASSCALLBACK GetFuncPtr();


// outside:
template<class InputType, class ReturnType, class ParamType1, class ParamType2>
CMenuItem<InputType, ReturnType, ParamType1, ParamType2>::CLASSCALLBACK
CMenuItem<InputType, ReturnType, ParamType1, ParamType2>::GetFuncPtr()
{}

[DNA7433]

one small problem on this line in the outside file

CMenuItem<InputType, ReturnType, ParamType1, ParamType2>::CLASSCALLBACK

i think its treating that as the data type for the function and it won't work if i put a semicolon like this

CMenuItem<InputType, ReturnType, ParamType1, ParamType2>::CLASSCALLBACK;

[CornedBee]

Actually it is the return type of the function GetFuncPtr(). It is a type defined inside the class, so I need the scope resolution operator and also the template parameters.

[DNA7433]

oh duh, i get it now
everything works perfectly, thanks

[DNA7433]

well that class compiles, but when i use it it starts giving me errors

this is where the function pointer is defined

template<class InputType, class ReturnType, class ParamType1, class ParamType2>
class CMenuItem
{
	public:
                                typedef ReturnType (*FUNCTION_PTR)(ParamType1, ParamType2);
                                void SetFuncPtr(FUNCTION_PTR Func);

	private:
		FUNCTION_PTR m_pFunc;
}

CRobots class...

CRobot* SendToJob(CJob* Job, int i);

and the function i'm attempting to call that isn't compiling right...

menuItem->SetFuncPtr(robots.SendToJob);
-----------------------------------------------------------------
error C2664: 'SetFuncPtr' : cannot convert parameter 1 from 'class CRobot *(class CJob *,int)' to 'class CRobot *(__cdecl *)(class CJob *,int)'

[CornedBee]

Is AddToJob a member function of a class? In that case, it wouldn't work anyway, because you can't assign a member function pointer to an ordinary function pointer. You can have special member function poiners, but they are specific to one class (can maybe be solved with template parameters too). Here is a pointer to a the AddToJob function, assuming AddToJob is a member function of CRobot.
typedef CRobot* (CRobot::*FUNC_PTR)(CJob*, int);

to call, you need a valid CRobot object, here it is robot:
// FUNC_PTR m_func;
robot.*m_func(pJob, 34);

if you have a pointer:
pRobot->*m_func(pJob, 34);

[DNA7433]

ok thanx

this whole thing has just turned into one huge mess

[CornedBee]

Maybe it's possible with templates:

template <class _RT, class _PT1, class _PT2, class _OT>
class x
{
typedef _RT (_OT::* FUNC_PTR)(_PT1, _PT2);
};

[DNA7433]

thats exactly how i have it set up, and then the user passes in a pointer to a class of type _OT which is stored in _OT* m_pClass;

then when i call it i do m_pClass->*m_pFunc(*m_pParam1, *m_pParam2);

and it tells me that the term does not evaluate to a function

[CornedBee]

maybe
m_pClass->(*m_pFunc)(*m_pParam1, *m_pParam2);

[DNA7433]

here is a small version i created to test just to make sure i wasn't doing something wrong on my big project

the code is exactly how i have it setup in my other project and as far as i can tell its also exactly what you've been telling me to do and it still gives the same error, and also adding ( ) create yet another compile error

#include<iostream>
#include<string>

using namespace std;

class AnotherClass
{
public:
	AnotherClass(){}

	void Me(void)
	{
		cout << "nothing\n";
	}

private:

};
////////////////////////////////////////////

template<class _Ty>
class Menu
{
public:
	typedef void (_Ty::*FUNC)(void);

	Menu(){}

	void SetFunc(FUNC func)
	{
		m_func = func;
	}

	void CallFunc(_Ty *SomeClass)
	{
		SomeClass->*m_func();
	}

private:
	FUNC m_func;
};
////////////////////////////////////////////

int main()
{
	AnotherClass b;
	Menu<AnotherClass> m;
	m.SetFunc(b.Me);
	m.CallFunc(&b);
	
	return 0;
}

[CornedBee]

m.SetFunc(b.Me);
This line works in VC++ but should be
m.SetFunc(AnotherClass::Me);
for standard compliance (the first does not compile on borland turbo c++)

This function call compiles on both compiles:
(SomeClass->*m_func)();

Test run gives correct result ("nothing")

[DNA7433]

thank you so much