How to use pointer to method as a parameter (when pointer to function is required)?

Question

I have some 3rd-part code:

class A(){
    public:
        void assingOnClickFunction(void (*function)(); 
};

I cannot change anything in that code. I want to pass to that A::assingOnClickFunction() my method of class B, void B::someFunction(). I have tried (all inside of the B class!):

a->assingOnClickFunction(this->someFunction);

But I get the error:

function call missing argument list; use '&B::someFunction' to create a pointer to member

So I have changed it to:

a->assingOnClickFunction(&B::someFunction);

But now there is ofc the error about the different types: (void(*)() and (&B::*)()

I cannot make B::someFunction() static (it uses a lot of non-static B's members and methods)!

So, is there an option to pass my B::someFunction() to the A::assingOnClickFunction(), not changing it to static and not changing anything in A class (A is not and cannot be aware of B, B includes A)?

As I have wrote, it's not static and I cannot change it to static. — PolGraphic, Feb 05 '13 at 20:21
Trying it gives an error: 'type cast' : cannot convert from 'void (__thiscall B::* )(void)' to 'void *' — PolGraphic, Feb 05 '13 at 20:23
Please google before asking - http://stackoverflow.com/questions/6852462/how-to-pass-a-method-as-parameter — djechlin, Feb 05 '13 at 20:25

score 3 · Accepted Answer · answered Feb 05 '13 at 20:23

3

If the member function you want to pass is not static, you cannot do that. The method in A accepts a function pointer to a function with no arguments, and a non-static member function has an implicit this pointer argument.

answered Feb 05 '13 at 20:23

Andy Prowl

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score 2 · Answer 2 · answered Feb 05 '13 at 20:26

2

In order to call a (non-static) method of an object, you need to know both the object and the method to call.

The assingOnClickFunction() function only takes a pointer to a function, so you cannot pass it the needed information.

Besides some horrible hacks, like implementing a function that has access to some global instance of your object, and calls the method throught that, it can't be done.

answered Feb 05 '13 at 20:26

Peter Allin

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2

Indeed, I was thinking about something like that 'hacks'. But I guess I should rebuild my code and make it in some other way (it would looks really horrible with global instances and functions with access to it). – PolGraphic Feb 05 '13 at 20:30

score 1 · Answer 3 · answered Feb 05 '13 at 20:26

1

A pointer to member function is not a pointer to function. If you have a function that takes an argument whose type is pointer-to-function, you cannot call it with a pointer to member function.

answered Feb 05 '13 at 20:26

Pete Becker

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How to use pointer to method as a parameter (when pointer to function is required)?

3 Answers3