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?

https://stackoverflow.com/questions/1485983/calling-c-class-methods-via-a-function-pointer Your function pointer actually has the signature `void (Main::*SIMPLECALLBK)(const char*)` which is not what your `typedef` says — Cory Kramer, Aug 11 '15 at 12:00
You're missing a `;` after the declaration of `helper` in your `Main` class. I doubt that's it though. — sweerpotato, Aug 11 '15 at 12:03

score 3 · Accepted Answer · answered Aug 11 '15 at 12:02

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 '15 at 12:02

Jarod42

190,553
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why its needs to be static ? – user63898 Aug 11 '15 at 12:07
@user63898 non-static member functions can only be called on an object. There is no object associated with `&Main::SessionHelper` – M.M Aug 11 '15 at 12:08

Waxo · Answer 2 · 2015-08-11T12:19:20.160

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 '15 at 12:19

answered Aug 11 '15 at 12:07

Waxo

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C++ pass function pointer with parameter to function

2 Answers2