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C++ syntax, calling a class member

deleyd (3)
In the following code example of the State Design Pattern, in the main code at the bottom it defines an instance of class Machine, and then calls Machine::off;. Why doesn't it instead call fsm.off;?
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  Machine fsm;

  Machine::off;

Then I tried imitating that by adding a class Abba, and then doing:
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  Abba a;
  Abba::DoStuff();

but that didn't work. Why?

Full code example:
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// StatePattern.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
using namespace std;
class Machine
{
  class State *current;
  public:
    Machine();
    void setCurrent(State *s)
    {
        current = s;
    }
    void on();
    void off();
};

class State
{
  public:
    virtual void on(Machine *m)
    {
        cout << "   already ON\n";
    }
    virtual void off(Machine *m)
    {
        cout << "   already OFF\n";
    }
};

void Machine::on()
{
  current->on(this);
}

void Machine::off()
{
  current->off(this);
}

class ON : public State
{
  public:
    ON()
    {
        cout << "   ON-ctor ";
    };
    ~ON()
    {
        cout << "   dtor-ON\n";
    };
    void off(Machine *m);
};

class OFF : public State
{
  public:
    OFF()
    {
        cout << "   OFF-ctor ";
    };
    ~OFF()
    {
        cout << "   dtor-OFF\n";
    };
    void on(Machine *m)
    {
        cout << "   going from OFF to ON";
        m->setCurrent(new ON());
        delete this;
    }
};

void ON::off(Machine *m)
{
  cout << "   going from ON to OFF";
  m->setCurrent(new OFF());
  delete this;
}

Machine::Machine()
{
  current = new OFF();
  cout << '\n';
}


class Abba
{
  public:
    void DoStuff(State *s)
    {
        cout << "Doing Stuff" << endl;
        
    }
};


int _tmain(int argc, _TCHAR* argv[])
{
  Machine fsm;

  Machine::off;
  Machine::on;

  Abba a;
  Abba::DoStuff();
}
kbw (9488)
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int main(int argc, char* argv[])
{
    Machine fsm;
    fsm.off();
    fsm.on();

    Abba a;
    Abba.DoStuff();

    return 0;
}


@L B, You're right.
Last edited on
LB (13399)
@kbw missing function call parameter list on lines 4 and 5, the code does nothing.
ne555 (10692)
void DoStuff(State *s) here you say that you are going to pass a parameter, so when you call that function you must pass a parameter 
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State Empire;
Abba Fernando;
Fernando.DoStuff( &Empire );


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    void on(Machine *m)
    {
        cout << "   going from OFF to ON";
        m->setCurrent(new ON());
        delete this;
    }
o_O
By the way, your last state will leak.
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