c++ class method callback Similar to std::thread

Question

Using std::thread you are able to pass a classes method as the function to call.

Syntax:

std::thread myThread(&MyClass::handler, this);

1.What is the syntax of my function to imitate this behavior to allow for passing of class methods to my own callback routines?

2.How do I store this reference in a variable?

ex:

Myclass temp;
myfunction(&Myclass::somefunc,temp);

So?

typedef void(*mycallbacktype)(const std::string& someperamiter);
void myfunction(???)

@user0042 Ok, so that seems to work.Any way to drop this to one line?: using std::placeholders::_1; callbacktype f_add_display2 = std::bind(&B::callbk, b, _1); s.startListen(f_add_display2); — Steven Venham
– Steven Venham, Commented Sep 19, 2017 at 18:58

Jodocus · Accepted Answer · 2017-09-19 19:08:30Z

1

1.What is the syntax of my function to imitate this behavior to allow for passing of class methods to my own callback routines?

It is called "pointer-to-member". See What are the Pointer-to-Member ->* and .* Operators in C++? Your second question should be answered by that.

answered Sep 19, 2017 at 19:08

Jodocus

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army007 · Accepted Answer · 2017-09-19 20:07:55Z

To take a member function pointer to MyClass which returns void and takes no additional parameter declare it like -

void myfunction(void (MyClass::*somefunction)(), MyClass* obj)
{
  (obj->*somefunction)();
}

Here void (MyClass::*somefunction)() means somefunction is a pointer to member function of MyClass that takes no additional (except for implicit MyClass* as first parameter) parameter and returns void. See this for more about member function pointer.

To make the function more generic like std::thread declare it as following- The first one takes any non-member function (aka. free function) of any type

template<class F, class... Args>  
void myfunction(F&& f, Args&&... args)
{
    f(std::forward<Args>(args)...);
}

and second one takes the member function pointer of any type of any class.

template <class R, class C, class... Args> 
void myfunction(R(C::*mf)(Args...), C* pc, Args&&... args)
{
    (pc->*mf)(std::forward<Args>(args)...);
}

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