c++ - How to call a non static member function from a static member function without passing class instance

Question

I need to call a non static member function from a static member function of the same class. The static function is a callback. It can receive only void as data, though which i pass a char*. So i cannot directly provide the class instance to the callback. I can pass a structure instead of char to the callback function. Can anyone give eg code to use the non static member function in a static member function . and use the structure in the static member function to use the instance of the class to call the non static member function?

Answer 1

Normally such a callback would look like this:

void Callback( void* data)
{
    CMyClass *myClassInstance = static_cast<CMyClass *>(data);
    myClassInstance->MyInstanceMethod();
}

Of course, you need to make sure, data points to an instance of your class. E.g.

CMyClass* data = new CMyClass();
FunctionCallingMyCallback( data, &Callback);
delete data;

Now, if I understand you correctly, you need to also pass a char*. You can either wrap both in a struct and unwrap it in the callback like so:

MyStruct* data = new MyStruct();
data->PtrToMyClass = new CMyClass();
data->MyCharPtr = "test";
FunctionCallingMyCallback( data, &Callback);
delete data->PtrToMyClass;
delete data;


void Callback( void* data)
{
    MyStruct *myStructInstance = static_cast<MyStruct *>(data);
    CMyClass *myClassInstance = myStructInstance->PtrToMyClass;
    char * myData = myStructInstance->MyCharPtr;
    myClassInstance->MyInstanceMethod(myData);
}

or, if you can modify the definition of CMyClass, put all the necessary data in class members, so that you can use a callback as in the first example.