C++ pass function pointer with parameter to function

Question

I think I have misunderstood how function pointers work. In this example:

class Helper
{
  public:

      typedef void (*SIMPLECALLBK)(const char*);
      Helper(){};
      void NotifyHelperbk(SIMPLECALLBK pCbk)
      { m_pSimpleCbk = pSbk; }
  private:
     SIMPLECALLBK m_pSimpleCbk;

}

// where i call the func
class Main
{
    public:
      Main(){};
    private:
      Helper helper
      void SessionHelper(const char* msg);

}

Main.cpp

void Main::SessionHelper(const char* msg)
{
   ....
} 

helper.NotifyHelperbk(&Main::SessionHelper);

I get the following error:

error C2664: 'Main::NotifyHelperbk' : cannot convert parameter 1 from 'void (__thiscall Main::* )(const char *)' to 'Helper::SIMPLECALLBK'
1>        There is no context in which this conversion is possible

What am I missing here?

stackoverflow.com/questions/1485983/… Your function pointer actually has the signature void (Main::*SIMPLECALLBK)(const char*) which is not what your typedef says — Cory Kramer
– Cory Kramer, Commented Aug 11, 2015 at 12:00
You're missing a ; after the declaration of helper in your Main class. I doubt that's it though. — sweerpotato
– sweerpotato, Commented Aug 11, 2015 at 12:03

Jarod42 · Accepted Answer · 2015-08-11 12:02:31Z

3

Main::SessionHelper is a non static method. So add static to it to be able to use it as function pointer. Or use member method pointer (you will need a instance to call it).

answered Aug 11, 2015 at 12:02

Jarod42

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2 Comments

user63898 Over a year ago

why its needs to be static ?

M.M Over a year ago

@user63898 non-static member functions can only be called on an object. There is no object associated with &Main::SessionHelper

Waxo · Accepted Answer · 2015-08-11 12:19:20Z

0

if you use c++11 you can use std::bind

class Helper
{
  public:
    void NotifyHelperbk(std::function<void(char*)> func){
    /* Do your stuff */
    func("your char* here");
}

And your main :

Main.cpp

Main m;

helper.NotifyHelperbk(std::bind(&Main::SessionHelper, m, std::placeholder_1));

edited Aug 11, 2015 at 12:19

answered Aug 11, 2015 at 12:07

Waxo

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