Error while writing State Design Pattern Code

[Pallav singh]

Hi All

i am getting Error while writing following code for state design
Pattern
kindly let me know How to Correct this Error ??

Thanks
Pallav Singh

+++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++

#include<iostre am.h>
using namespace std;

class state;

class Machine
{
class state * current;
public :
Machine();

void setcurrentstate (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<<"Destruc tor invoked \n ";}
~ON() {cout<<"Constru ctor invoked \n ";}
void off(Machine * m);
};

class OFF : public state
{
public :
OFF() {cout<<"Destruc tor invoked \n ";}
~OFF() {cout<<"Constru ctor invoked \n ";}
void on(Machine * m)
{cout<<"Going from OFF to ON";
m->setcurrentstat e( new ON() );
delete this;
}
};



Machine::Machin e()
{
current = new OFF();
cout<<"Machine constructor Called "<<endl;
}


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




int main()
{

void (Machine::*ptrs[] )() = { Machine::off, Machine::on }; // Error
Point
Machine FSM;
int num;
while(1)
{ cout <<"Enter 0 / 1 : ";
cin >num;
(FSM.*ptrs[num])();
}

return 0;
}

+++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++

[Daniel T.]

Re: Error while writing State Design Pattern Code

Pallav singh <singh.pallav@g mail.comwrote:

int main()
{
>
void (Machine::*ptrs[] )() = { Machine::off, Machine::on }; // Error
Point

void (Machine::*ptrs[])() = { &Machine::of f, &Machine::on };

[Eric Pruneau]

Re: Error while writing State Design Pattern Code


"Pallav singh" <singh.pallav@g mail.coma écrit dans le message de news:
2c1ee6ab-5e22-48e5-8a75-f6c6d438a841...l egroups.com...

Hi All
>
i am getting Error while writing following code for state design
Pattern
kindly let me know How to Correct this Error ??
>
Thanks
Pallav Singh
>
+++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++
>
#include<iostre am.h>
using namespace std;
>
class state;
>
class Machine
{
class state * current;
public :
Machine();
>
void setcurrentstate (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<<"Destruc tor invoked \n ";}
~ON() {cout<<"Constru ctor invoked \n ";}
void off(Machine * m);
};
>
class OFF : public state
{
public :
OFF() {cout<<"Destruc tor invoked \n ";}
~OFF() {cout<<"Constru ctor invoked \n ";}
void on(Machine * m)
{cout<<"Going from OFF to ON";
m->setcurrentstat e( new ON() );
delete this;
}
};
>
>
>
Machine::Machin e()
{
current = new OFF();
cout<<"Machine constructor Called "<<endl;
}
>
>
void ON::off(Machine * m)
{
cout<<"Going from ON to OFF";
m->setcurrentstat e( new OFF() );
delete this;
}
>
>
>
>
int main()
{
>
void (Machine::*ptrs[] )() = { Machine::off, Machine::on }; // Error
Point
Machine FSM;
int num;
while(1)
{ cout <<"Enter 0 / 1 : ";
cin >num;
(FSM.*ptrs[num])();
}
>
return 0;
}
>
+++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++

Well I don't get any errors while compiling it with intel c++ compiler...
Except that I changed :

void (Machine::*ptrs[] )() = { Machine::off, Machine::on }; // Error
Point

for

void (Machine::*ptrs[] )() = { Machine::off, Machine::on }; // Error Point

I guess it is a typo error...

[Daniel T.]

Re: Error while writing State Design Pattern Code

In article
<2c1ee6ab-5e22-48e5-8a75-f6c6d438a841@w3 4g2000prm.googl egroups.com>,
Pallav singh <singh.pallav@g mail.comwrote:

Hi All
>
i am getting Error while writing following code for state design
Pattern
kindly let me know How to Correct this Error ??
>
Thanks
Pallav Singh

Results from compiling in: http://www.comeaucomputing.com/tryitout and
my own observations...

+++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++++++++ +++++++++
>
#include<iostre am.h>

(From comeau)
<iostream.his not a Standard header, use <iostreaminstea d.

using namespace std;
>
class state;
>
class Machine
{
class state * current;

keyword 'class' unnecessary above.

public :
Machine();
>
void setcurrentstate (state * s)
{ current = s ; }
>
void on();
void off();
};
>
class state
{
public :
virtual void on(Machine * m)
{cout<< " Already On \n"; }

Above, and in general, your use of whitespace is inconsistent,
especially inside quotes.

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<<"Destruc tor invoked \n ";}
~ON() {cout<<"Constru ctor invoked \n ";}
void off(Machine * m);
};
>
class OFF : public state
{
public :
OFF() {cout<<"Destruc tor invoked \n ";}
~OFF() {cout<<"Constru ctor invoked \n ";}
void on(Machine * m)
{cout<<"Going from OFF to ON";
m->setcurrentstat e( new ON() );
delete this;
}
};
>
>
>
Machine::Machin e()
{
current = new OFF();
cout<<"Machine constructor Called "<<endl;
}
>
>
void ON::off(Machine * m)
{
cout<<"Going from ON to OFF";
m->setcurrentstat e( new OFF() );
delete this;
}
>
>
>
>
int main()
{
>
void (Machine::*ptrs[] )() = { Machine::off, Machine::on }; // ErrorPoint

(From comeau)
error: nonstandard form for taking the address of a member function
void (Machine::*ptrs[] )() = { Machine::off, Machine::on };
^

(From comeau)
error: nonstandard form for taking the address of a member function
void (Machine::*ptrs[] )() = { Machine::off, Machine::on };
^

Machine FSM;
int num;
while(1)
{ cout <<"Enter 0 / 1 : ";
cin >num;
(FSM.*ptrs[num])();
}
>
return 0;

(From comeau)
warning: statement is unreachable
return 0;
^

}