How to point to a function of a referenced class?

Question

Is there a way to have a pointer to a function inside a referenced class?

I've tried replacing the reference to a class with another pointer, did not work.
I've also tried using -> instead of ., no luck.

class First {
  void FunToPointTo();
};
class Second {
  First &reference;
  void (*pointer)();
  Second(First &first);
};

Second::Second(First &first) : reference(first) {
  pointer = reference.FunToPointTo;
}

Error: cannot convert 'First::FunToPointTo' from type 'void (First::)()' to type 'void (*)()'

Now I am trying to somehow make my pointer into void (First::)(), but I don't know the exact syntax.

Help is greatly appreciated, also please excuse my lack of knowledge as I am just starting c++.

You're looking for `void (First::*pointer)();`, and `&First::FunToPointTo`. Calling looks like `(object.*pointer)();`. — Quentin, Feb 12 '19 at 14:32
Pointer on (function) member is different than Pointer on function. — Jarod42, Feb 12 '19 at 14:34
No, it's of a different type, fundamentally incompatible with `void (*)()`. — n. m. could be an AI, Feb 12 '19 at 14:34
@SamerTufail I don't think this question would be useful in the future, but it would be mean to leave OP hanging. — Quentin, Feb 12 '19 at 14:36
Look at [pointer](https://en.cppreference.com/w/cpp/language/pointer), section "Pointers to member functions". — Jarod42, Feb 12 '19 at 14:36
I once wrote an answer regarding member function pointers with a little sample: [SO: What is the meaning of this star (*) symbol in C++? — Pointer to member](https://stackoverflow.com/a/50384782/7478597). May be, it helps. — Scheff's Cat, Feb 12 '19 at 14:41

score 1 · Accepted Answer · edited Feb 12 '19 at 14:55

1

Your pointer type should be

void (First::*ptr)()

And assign with

&First::FunToPointTo

Since you need to specify the function is from class First.

edited Feb 12 '19 at 14:55

Guillaume Racicot

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answered Feb 12 '19 at 14:39

tomer zeitune

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I don't need a general 'FunToPointTo' I need the one inside the referenced class. – Feb 12 '19 at 14:49
@OgnjenIlic I know but if you really think what a function is it's a piece of code that takes argumentsand if it's not a static function it has a pointer to the object named "this" . in this case you call the function with the object you want to send to the "this" keyword like that : reference.*ptr(); . Someone already wrote this I see – tomer zeitune Feb 12 '19 at 14:55
@Quentin: See [this](https://en.cppreference.com/w/cpp/language/pointer#Pointers_to_functions) – wallyk Feb 12 '19 at 15:00
2

@wallyk your article clearly states you should use the & operator for member functions look at the pointer to member functions section. It is a good article btw – tomer zeitune Feb 12 '19 at 15:03
@Quentin: tomer is quite right. I have deleted my earlier comment. – wallyk Feb 12 '19 at 15:51
@tomerzeitune: Thanks. I wonder why the rules are different for member functions? – wallyk Feb 12 '19 at 15:52
@wallyk I think they are treated more like members rather than functions. It does make some sense – tomer zeitune Feb 12 '19 at 16:22
@wallyk as with many other quirks, this might be a remnant of compatibility with C. – Quentin Feb 12 '19 at 16:38

How to point to a function of a referenced class?

1 Answers1