CODEWITHSUNDEEP
c++parameter-passing
bmkorkut
bmkorkut

Reputation: 616

Passing class member function in non-class member function's parameter

How can I pass a class member function to a non-class member function's parameter? I am getting the following compile error:

error: argument of type ‘void (MyNamespace::MyClass::)(int*)’ does not match ‘void (*)(int*)’

Library.h

typedef void (*testCallback)(int* iParam);
void UsingTheFoo(testCallback Callback);

Library.cpp

void UsingTheFoo(testCallback Callback)
{
  int *p_int = new int;
  *p_int = 5;
  Callback(p_int);
}

MyClass.cpp

namespace MyNamespace
{

    void MyClass::fooCB(int* a)
    {
        printf("hey! %d\n", *a);
    }


    void MyClass::testo()
    {
        UsingTheFoo(fooCB);
    }

} // MyNamespace

I can not change the code in "Library", I need to use "UsingTheFoo" in MyClass member functions. I am aware my way is wrong, I searched and found similar questions but couldn't understand (braindead at the end of shift :) ) any of them completely to adapt for my problem.

I've already read: http://www.parashift.com/c++-faq-lite/pointers-to-members.html :S

Upvotes: 0

Views: 598

Answers (3)

Dan
Dan

Reputation: 2109

A member function isn't a regular function.
Think of it as a function with signature (className *pthis,...) where .. is the signature you would think of. You can still do this, but you would want std/boost::bind and a function object instead of a callback. Or as others have posted, you can make it static.

so perhaps you might want something like

typedef function<void (int*)> TCallback
void UsingTheFoo(TCallback, Callback);

MyClass class_object

with callback

TCallback cb = bind(std::ref(class_object),MyClass::fooCB);

Upvotes: 1

Robᵩ
Robᵩ

Reputation: 168626

fooCB, in your example, must be a static class member:

class MyClass {
public:
    static void MyClass::fooCB(int* a);
    ...
}

Upvotes: 0

Alecs
Alecs

Reputation: 2316

Make method that you wanna to pass as a callback as static. You've got this error because all methods have implicitly first parameter - pointer to an object, this, so their prototype doesn't correspond to callbacks'.

Upvotes: 2

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