C++ calling static function pointer

Question

I would like to forward a callback to a function pointer. So I declare a static (int*) m_pointer1, as well as a method void RegisterCallback1( (int*)fct)

in class1.h:

public:
   int RegisterCallback1( int (*fct) );
private:
   static int (*m_Callback1);

in class1.cpp:

int class1::RegisterCallback1( int (*fct) )
{
    m_Callback1= fct;
}

then, I want to forward the callback to the function pointer:

void class1::Callback1()
{
   (*m_Callback1)();
}

But I get a compiler error "Expression must have (pointer-to)- function type I have followed tutorial and read about function pointers and they seem to do it this way without any problems. Any ideas why?

EDIT: So, I declare (int*)(void)m_Callback1 -Visual Studio requires a void there...- Then how do I call the registerCallback function with the argument?

class1.RegisterCallBack1(  ??? - class2::callback -??? );

Dave · Accepted Answer · 2012-04-24 19:19:08Z

7

static int (*m_Callback1) does not declate a function pointer, just a pointer to int: you forgot about the parameter list. You meant:

static int (*m_Callback1)();

and

int RegisterCallback1( int (*fct)() );

answered Apr 24, 2012 at 19:19

Dave

11.2k3 gold badges34 silver badges55 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

David Menard Over a year ago

Thats great, but then how to I pass it to RegisterCallback1? I tried something like class1.RegisterCallback1( (int*) class2::callback ); and many combinations, they all seems to give me an error? Always something with argument of type int* incompatible with (int*)()

Oliver Charlesworth · Accepted Answer · 2012-04-24 19:19:01Z

6

You haven't declared a function pointer, you've declared a normal data pointer. You are missing () at the end of the declaration.

answered Apr 24, 2012 at 19:19

Oliver Charlesworth

274k34 gold badges591 silver badges687 bronze badges

3 Comments

David Menard Over a year ago

Thats great and all, but then how do I call the registerCallback1 function with an argument? class1.RegisterCallBack1( ??? - class2::callback -??? );

ildjarn Over a year ago

@David : Assuming class2::callback is static, c1.RegisterCallBack1(&class2::callback).

David Menard Over a year ago

this gives out another error: argumen of type void(__stdcall )() is not compatible with parameter of type void()(). If I add __stdcall to function pointer decleration, I get linking errors, saying that m_callback1() cannot be found in class1 (not class2)

TemplateRex · Accepted Answer · 2012-04-24 19:49:51Z

1

You can try to limit the missing () errors pointed out by Oli and Dave by using a typedef for the callback function's signature: typedef int (*)() CallBack; This would at least have the merit of letting you think once about the precise number of brackets rather than at every point in your code where you use such a function.

edited Apr 24, 2012 at 19:49

answered Apr 24, 2012 at 19:28

TemplateRex

70.9k21 gold badges176 silver badges316 bronze badges

Collectives™ on Stack Overflow

C++ calling static function pointer

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related