Pointer to member function

[ritzmax72]

Here is the program which uses pointers to members, variables and functions.
Pointer to variables are done without error as i checked keeping the blocks with problem in comment line.
The problem is with member function. I did it as it was given in book and even saw same format on net.
The errors are like this:cannot call member function 'void' sejal::get without object.
The compiler is Bloodshed's Dev c++

#include<stdio.h>
#include<conio.h>
#include<iostream>
using namespace std;
class sejal
{
      public:
      int y;
             void get();
             void put();
             friend sejal add(sejal,sejal);
             };
             void sejal::get()
             {
                  cout<<"\nEnter the value";
                  cin>>y;
                  };
                  void sejal::put()
                  {
                       cout<<"\nThe value is :"<<y;
                       };
                      sejal add(sejal m, sejal k)
                       {
                                 sejal o;
                                 o.y=m.y+k.y;
                                 cout<<"The addition value is:";
                                 return(o);
                                 };
                                 main()
                                 {
                                       sejal a,b,c;
                                       a.get();
                                       b.get();
                                       c=add(a,b);
                                       c.put();
                                       /*using pointer to member variable*/
                                       int sejal::*p=&sejal::y;
                                       cout<<"\nPrinting using pointer to member"<<":"<<a.*p<<"\n"<<b.*p;
                                       cout<<"Now taking pointer to object";
                                       sejal *i;
                                       i=&a;
                                       sejal *h;
                                       h=&b;
                                       cout<<"\n"<<"Printing using pointer to object"<<i->*p<<"\n"<<h->*p;
                                       cout<<"Using pointers to member function";
                                       void (sejal::*pf)(void)=&sejal::get();
                                       a.*pf();
                                       b.*pf();
                                       void (sejal::*pg)(void)=&sejal::put();
                                       a.*pg();
                                       b.*pg();
                                       cout<<"\nNow using pointer to object\n";
                                       i->*pf();
                                       h->*pf();
                                       cout<<"\nPrinting";
                                       i->*pg;
                                       h->*pg;
                                       cout<<"Done";
                                       getch();
                                       }

[manasij7479]

1. main() must return an integer or your program will not compile on a modern compiler.

2. You've seriously misunderstood(If you've written this yourself) almost everything regarding pointers to members and pointers to objects.
Read [33] Pointers to member functions ..Updated!.., C++ FAQ

3. Your indentation is awful; you're writing code, not making a staircase.

[tabstop]

I'll have to disagree with the honorable manasij on point 2; the only thing wrong I see with the syntax is that this

a.*pf();

needs to be this

(a.*pf)();

(and of course ditto on the following lines). (EDIT: Oh, and the last set of pg calls are missing their last () as well, which seem to have migrated to the get and put on the lines defining pf and pg.)

We agree wholeheartedly on point 3, though.

[manasij7479]

I'll have to disagree with (:P) manasij on point 2; the only thing wrong I see with the syntax is that this.

What he basically is doing:

class X
{
public:
    void foo();
};
void (*bar)();
int main()
{
    bar = X::foo;
    return 0;
}

which apparently is invalid.

Please correct me if I'm wrong.

[cyberfish]

Imagine you have to write a 1000 lines file... do you tilt your screen to read your code?

[Ushakal]

manasij is right, you can't assign a non-static member function to a function pointer. The code manasij posted would work if the member function foo() was made static (i.e., "static void foo();").

[Elysia]

>>void (sejal::*pf)(void)=&sejal::get();
This should be (at the very least)
void (sejal::*pf)(void)=&sejal::get;

Also, in manasij7479's example, bar = X::foo; is wrong.
It should be bar = &X::foo;

[manasij7479]

Also, in manasij7479's example, bar = X::foo; is wrong.
It should be bar = &X::foo;

That is also wrong.

[Elysia]

Let's just put out correct code on calling member functions to avoid confusion...

class X
{
public:
    void foo();
};

typedef void (X::*X_foo_t)();

int main()
{
    X_foo_t bar = &X::foo;
    X x;
    (x.*bar)();
    return 0;
}

I think I may be half to blame for not entirely reading the thread correctly...

[_Mike]

Let's just put out correct code on calling member functions to avoid confusion...

class X
{
public:
    void foo();
};

typedef void (X_foo_t)();

int main()
{
    X_foo_t* bar = X::foo;
    X x;
    (x.*bar)();
    return 0;
}

I think I may be half to blame for not entirely reading the thread correctly...

First you correct manasij7479 for not using & to get the address of foo, and then you do the same thing yourself

typedef void (X::*X_foo_t)();
X_foo_t bar = &X::foo;

[Elysia]

Yeah, I'm getting forgetful and not compiling code.
But thankfully there's people like you who can correct me!