static member functions

This is sort of a dumb question but I've been wondering about it for many months. I wondering if a class's static member function is equivelent to a global function but in a different namespace. Can a class be effectively called a namespace?

>Can a class be effectively called a namespace?
Yes, more or less.

Can a class be effectively called a namespace?

My impression is: no. A namespace just adds a qualifying name to a function or variable, and you can call the function or variable at any time using the full name:

Code:

#include<iostream>
#include<string>
using namespace std;

namespace Apple
{
	int num = 10;
}

int main()
{
	cout<<Apple::num<<endl;

	return 0;
}

Normally, class functions or variables can only be called by class objects, but a public static function or variable in a class is an exception to that rule, and it is called with a similar syntax as when using a namespace:

Code:

#include<iostream>
#include<string>
using namespace std;

class Apple
{
public:
	static int num;
};

int Apple::num = 10; //initialize the static variable

int main()
{
	cout<<Apple::num<<endl; 
	
	return 0;
}

However, in general static functions and variables seem very different from a function or a variable in a namespace. For instance, a static variable can have a private access specifier, which limits access to the variable--only class objects that call class methods can access the variable.

Code:

#include<iostream>
#include<string>
using namespace std;

class Apple
{
private:
	static int num;

public:
	void display()
	{
		cout<<num<<endl;
	}

	void set_num(int n)
	{
		num = n;
	}

};

int Apple::num = 10; //initialize the static variable

int main()
{
	Apple myApple;
	myApple.display();

	cout<<Apple::num<<endl;  //error: access denied

	return 0;
}

Variables in namespaces don't have access specifiers.

In addition, every object of a class has a pointer to the static variable, so when you change a static variable it is reflected in all the objects of the class:

Code:

#include<iostream>
#include<string>
using namespace std;

class Apple
{
public:
	static int num;
};

int Apple::num = 10; //initialize the static variable

int main()
{
	cout<<Apple::num<<endl;
	
	Apple apple1, apple2;

	cout<<apple1.num<<" "<<apple2.num<<endl;
	Apple::num = 40;
	cout<<apple1.num<<" "<<apple2.num<<endl;

	return 0;
}

A namespace variable has no comparable functionality.

Namespaces allow you to declare using directives so you can forgo having to use the qualifying namespace name, which you can't do with a static class variable or function.

edit:

Originally Posted by Prelude

>Can a class be effectively called a namespace?
Yes, more or less.

Uh, oh.

Originally Posted by Prelude

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For senior member use only

...wish I had been paying attention.