Can a C Class Member Function Be Used as a C Callback Function?

Using a C Class Member Function as a C Callback Function

It is possible to register a C class member function as a C callback function, but there are certain requirements to satisfy.

Q1: First of all is it possible to register a C class member function like I am trying to do and if so how?

A1: Yes, it is possible to register a C class member function as a callback function if the function is declared as a static function. Static member functions do not have an implicit 'this' pointer as their first argument, unlike non-static member functions. This allows them to be compatible with the signature of a C callback function.

Q2: Is there a alternate/better way to tackle this?

A2: Here are some alternative options:

• Create a free function: Implement a separate free (non-member) function that matches the callback function signature and then register it with the library.
• Use a function pointer: Create a function pointer to a static member function of the C class and pass the function pointer to the library. This requires that the library supports using function pointers as callback functions.
• Use a wrapper function: Define a wrapper function outside the class that calls the desired class member function and has a signature compatible with the C callback function. Then, register the wrapper function with the library.

Example Using a Static Member Function:

class A {
public:
    A() { register_with_library(&A::e); }
    ~A() {}

    static int e(int *k, int *j) {
        return 0;
    }
};

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