Question

I’m trying to get something like this to work by passing a function pointer. I know you can just pass a pointer of the first class to the second and get the second to fire a member function of the first class through the pointer. But I don’t want the second class to rely on knowing who the first class is. This is more like coding style i’m looking for to achieve this. Thanks

//////////////////////////////////////////////////
class Second
{
public:
    Second::Second(void (*SecondTriggered)(void));
};

Second::Second(void (*SecondTriggered)(void))
{
    SecondTriggered();
}


//////////////////////////////////////////////////
class First
{
public: 
    First::First();
    void SecondTriggered();
    Second *second;
};

First::First(){
        printf("first class was created"); 
    second = new Second(SecondTriggered);
}

void First::SecondTriggered(){
    printf("second class was created and responded"); 
}

/////////////////
int main()
{
    First *first = new First();
 } 

I get this error:

error C3867: 'First::SecondTriggered': function call missing argument list; 
use '&First::SecondTriggered' to create a pointer to member

Any ideas.

Answer 1

You are trying to pass a non-static class member where a standalone function is expected. To do what you are attempting, you would have to do something like the following instead:

class Second
{
public:
    Second::Second(void (*SecondTriggered)(void*), void *arg);
};

Second::Second(void (*SecondTriggered)(void*), void *arg)
{
    SecondTriggered(arg);
}


//////////////////////////////////////////////////
class First
{
public: 
    First::First();
    static void SecondTriggered(void *arg);
    Second *second;
    void DoSomething();
};

First::First(){
    printf("first class was created"); 
    second = new Second(&SecondTriggered, this);
}

void First::SecondTriggered(void *arg){
    printf("second class was created and responded"); 
    static_cast<First*>(arg)->DoSomething();
}

void First::DoSomething(){
    printf("first class did something");
}

/////////////////
int main()
{
    First *first = new First();
 }