Callback function pointers C++ with/without classes

Question

I got stuck. I am trying to form a function that will eat classless function pointers and ones from objects. Here is my current code that hopefully explains more.

(It should run on a Arduino, so I cannot use big libraries.)

First off, I am using this library for the Arduino:

/* SimpleTimer - A timer library for Arduino.
 * Author: [email protected]
 * Copyright (c) 2010 OTTOTECNICA Italy
 */

Which takes functions which it calls on a set timer interval of this type:

typedef void (*timer_callback)(void);

As far as my knowledge goes, it's a classles function, the webpage Pointers to member functions got me really far but, not far enough. Probably a terminology deficit on my side.

Now, I have made my own class which I would like in turn to use this SimpleTimer library. But if I feed the SimpleTimer my class functions, it does not like them (what I understand). But how would it be possible to make this happen without altering the SimpleTimer library.

So there is the class Robot, which has Robot::halt(). I want the robot to move forward for a set amount of time. Like so:

void Robot::forward(int speed, long time) {
    reset();
    timer.setTimer(time, c_func, 1);

    analogWrite(l_a, speed);
    analogWrite(r_a, speed);
    isMoving(true);
}

void Robot::halt() {
    __isMoving = false;
    digitalWrite(r_a, LOW);
    digitalWrite(r_b, LOW);
    digitalWrite(l_b, LOW);
    digitalWrite(l_a, LOW);
}

The c_func variable is a classless function at this point, but I would like to use the Robot::halt function. I have looked, read, learned but haven't succeeded yet. I just can't seem to wrap my head around this one because I am missing some angle.

I tried:

timer.setTimer(time, (this->*halt), 1);
timer.setTimer(time, Robot::*halt, 1);
timer.setTimer(time, &Robot::halt), 1);

But it would all amount to the same problem/ me just stabbing in the dark here...

EDIT

Earlier, I said not wanting to change the SimpleTimer library code. I want to comeback on this one, I guess altering it there would be the better option.

Thanks for all the current answers already, I was only allowed to flag one as a viable answer, actually everyhting I read here was extremely helpful.

To continue this, changing the SimpleTimer code. This class needs to have a reference to the object that holds my "halt" function, right? So, overloading the settimer function to something that takes my object and my function as two seperate pointers would work...? I think I am getting the hang of this but, I am not there yet with my head.

EDIT

I don't know who came with this one again but, anyone finding this thread. If found Member Function Pointers and the Fastest Possible C++ Delegates to give a very nice introduction in function pointers and member function pointers.

EDIT

Got it working, changed the SimpleTimer library to use this Delegate system: http://www.codeproject.com/KB/cpp/FastDelegate.aspx

It integrated very nicely, and it could be nice to have a standard Delegate system like this in the Arduino library.

Code as in test (working)

typedef

typedef FastDelegate0<> FuncDelegate;

Code in robot class:

void Robot::test(){
    FuncDelegate f_delegate;
    f_delegate = MakeDelegate(this, &Robot::halt);

    timer.setTimerDelg(1, f_delegate, 1);
}

void Robot::halt() {
    Serial.println("TEST");
}

Code in SimpleTimer class:

int SimpleTimer::setTimerDelg(long d, FuncDelegate f, int n){
    f();
}

Arduino prints TEST in the console.

Next step putting it in an array, don't see a lot of problems there. Thanks everyone, I can't believe the stuff I learned in two days.

What's that smell? Is that the smell of...? Success!

For the ones interested, the used Delegate system does not amount to memory capacity issues: With FastDelegate

AVR Memory Usage
----------------
Device: atmega2560

Program:   17178 bytes (6.6% Full)
(.text + .data + .bootloader)

Data:       1292 bytes (15.8% Full)
(.data + .bss + .noinit)


Finished building: sizedummy

Without FastDelegate:

AVR Memory Usage
----------------
Device: atmega2560

Program:   17030 bytes (6.5% Full)
(.text + .data + .bootloader)

Data:       1292 bytes (15.8% Full)
(.data + .bss + .noinit)


Finished building: sizedummy

Answer 1

You can do this by making a functor object, that acts as a proxy between the timer code and your code.

class MyHaltStruct
{
public:
    MyHaltStruct(Robot &robot)
        : m_robot(robot)
        { }

    void operator()()
        { robot.halt(); }

private:
    Robot &m_robot;
}

// ...

timer.setTimer(time, MyHaltStruct(*this), 1);

Edit

If it can't be done via a functor object, you could global variables and functions instead, maybe in a namespace:

namespace my_robot_halter
{
    Robot *robot = 0;

    void halt()
    {
        if (robot)
            robot->halt();
    }
}

// ...

my_robot_halter::robot = this;
timer.setTimer(time, my_robot_halter::halt, 1);

This only works if you have one robot instance though.