Array of member functions

Hi,
I want to implement a statemachine using an array of member function pointers instead of using switch-case statements:

This is the original situation:

Code:

class MyClass
{
   private:
    UCHAR m_ucState;
   public:
    BOOL HandleState();
    BOOL HandleState_1();
    BOOL HandleState_2();
    BOOL HandleState_3();
}

BOOL MyClass::HandleState()
{
   switch(m_ucState)
   {
      case 1:
         return HandleState_1();
      case 2:
         return HandleState_2();
      case 3:
         return HandleState_3();
   }
}

I want to change the HandleState function to something like this:

Code:

BOOL MyClass::HandleState()
{
   return m_myStateHandlers[m_ucState]();
}

Can anyone help me how I should declare the 'm_myStateHandlers' array? I should be a membervariable and all HandleState_... functions are not static.

Thanks in advance,

Ward

Can anyone help me how I should declare the 'm_myStateHandlers' array

You declare any array by specifying its size and the type of things you will store in the the array. What does the type 'pointer to member function' look like? See this current thread:

Pointer to a Member Function

BOOL (*m_myStateHandlers[3])(void);

This was not the problem, but I can not fill it up.

Code:

BOOL (*m_myStateHandlers[3])(void);

Shouldn't this be:

Code:

static BOOL (MyClass::*m_myStateHandlers[3])(void);

I guess it must be a pointer to a member function instead of a pointer to a function, also i believe you can use it as static since the methods are not supposed to move and that way you'll only have to initialize them once. About the initialization part i'm still trying to figure it out...

I can be sooooo wrong though, cheers

Originally Posted by Ward

BOOL (*m_myStateHandlers[3])(void);

This was not the problem, but I can not fill it up.

Code:

class MyClass
{
   private:
    UCHAR m_ucState;
    BOOL (*m_myStateHandlers[3])(void);
   public:
    MyClass();
    BOOL HandleState();
    BOOL HandleState_1();
    BOOL HandleState_2();
    BOOL HandleState_3();
};

MyClass::MyClass()
{
   int i = 0;
   m_myStateHandlers[i++] = &HandleState_1;
   m_myStateHandlers[i++] = &HandleState_2;
   m_myStateHandlers[i++] = &HandleState_3;
}

BOOL MyClass::HandleState()
{
   return (*m_myStateHandlers[m_ucState])();
}

Rather than an index such as m_ucState and a separate array of function pointers, how about using a single pointer to member function to contain the state information? Something along this line:

Code:

#include <iostream>

class FSM
{
   void (FSM::*pmf)(); // pointer to member function for current state
   void init()   { std::cout << "init"   << '\n'; pmf = &FSM::idle;   }
   void idle()   { std::cout << "idle"   << '\n'; pmf = &FSM::active; }
   void active() { std::cout << "active" << '\n'; pmf = &FSM::idle;   }
public:
   FSM(void (FSM::*pmf_)() = &FSM::init ) : pmf(pmf_) {}
   void run()
   {
      (this->*pmf)();
   }
};

int main() 
{
   FSM fsm;
   for ( int i = 0; i < 5; ++i )
   {
      fsm.run();
   }
   return 0;
}

/* my output
init
idle
active
idle
active
*/

Answer to 'homeyg':
I've tried something similar like you posted last. But I got compiler errors. I will verify my code against yours and test it again.
Thanks you.

Answer to 'Dave_Sinkula':
This is an interesting alternative way of working! At first sight is seems very difficult to perform debugging on it (keeping the overview of the states in sight), but I will surely test this out.
Thanks.

Kind regards,

Ward

Some debuggers might show the current function name, which would tell you the state.