Accessing a class' member functions

Accessing a class' member functions

[Shriramana Sharma]

I need to use a class' member functions without creating an instance of that 
class. Is that possible? I have seen someone do this in their C++ library but 
it does not work for me, so I am wondering what I did wrong.

-- 

Tux #395953 resides at http://samvit.org
playing with KDE 3.51 on SUSE Linux 10.0
$ date [] CCE +2006-03-26 W12-7 UTC+0530

Re: Accessing a class' member functions

[Steve Graegert]

On 3/26/06, Shriramana Sharma <samjnaa@gmail.com> wrote:
> I need to use a class' member functions without creating an instance of that
> class. Is that possible? I have seen someone do this in their C++ library but
> it does not work for me, so I am wondering what I did wrong.

What you've have seen are static member functions.  They can be called
withouth creating an instance of the class they are defined in.

Please note that static member functions can only access global data
or static class data and can not be declared virtual.  Since stattic
member functions exist without class instances, you cannot use the
implicit this pointer to access non-static members.

To access static members you simply use the class name and append the
member using the scope operator: MyClass::myStaticMember.

Example:

-- BEGIN ---
#include <iostream>
#include <cstdlib>
#include <ctime.h>

class C {
private:
    static const int MAX_NUM = 10;
public:

    static void get_num () {
        srand((unsigned)time(NULL));
        return (int)(MAX_NUM * rand() / (RAND_MAX + 1.0));
    }
};

int main(void) {
    cout << C::get_num() << "\n";
}

--- END ---

	\Steve

Re: Accessing a class' member functions

[Shriramana Sharma]

Sunday, 26 March 2006 13:45 samaye Steve Graegert alekhiit:

> Please note that static member functions can only access global data
> or static class data and can not be declared virtual.

So if I want some globally accessible function that is not limited to 
accessing global or static data what should I do?

-- 

Tux #395953 resides at http://samvit.org
playing with KDE 3.51 on SUSE Linux 10.0
$ date [] CCE +2006-03-26 W12-7 UTC+0530

Re: Accessing a class' member functions

[Steve Graegert]

On 3/26/06, Shriramana Sharma <samjnaa@gmail.com> wrote:
> Sunday, 26 March 2006 13:45 samaye Steve Graegert alekhiit:
>
> > Please note that static member functions can only access global data
> > or static class data and can not be declared virtual.
>
> So if I want some globally accessible function that is not limited to
> accessing global or static data what should I do?

If you are in a situation like that, you either have poorly designed
the application or you have not fully understood the nature of the
product you're using.

Anyway, if you desperately need this functionality you may want to
write an appropriate accessor method that instantiates the class in
question and returns the non-static member from within a static
context:

--- BEGIN ---
#include <iostream>

using namespace std;

class D {
private:
    int num;
public:
	D() { num = 3; }
	int get_num() {
		return num;
	}
};

class C {
public:
	static int get_num() {
		D *d = new D;
		return d->get_num();
	}
};

int main(void) {
	cout << "C::get_num(): " << C::get_num() << endl;
	return 0;
}
--- END ---

The example prints 3 on stdout.

	\Steve

Re: Accessing a class' member functions

[Glynn Clements]

Shriramana Sharma wrote:

> > Please note that static member functions can only access global data
> > or static class data and can not be declared virtual.
> 
> So if I want some globally accessible function that is not limited to 
> accessing global or static data what should I do?

Huh? What other data do you want to access? To access the member
variables of an instance, you need to actually /have/ an instance.

-- 
Glynn Clements <glynn@gclements.plus.com>