non-static vs. static function and variable

Question

I have one question about static and non-static function and variable.

1) non-static function access static variable.

It's OK!

class Bar
{
public:

     static int i;

     void nonStaticFunction() {

         Bar::i = 10;

     }

};

int Bar::i=0;

2) non-static function access non-static variable

Definitely OK!

3) static function access static variable&funciton

Definitely OK!

4) static function access non-static function

It's OK

class Bar
{
public:
     static void staticFunction( const Bar & bar)
     {
         bar.memberFunction();

     }

     void memberFunction() const
     {

     }

}

5) static function access non-static variable

It's OK or not OK? I am puzzled about this!

How about this example

class Bar
{
public:
     static void staticFunction( Bar & bar)
     {
         bar.memberFunction();

     }

     void memberFunction()
     {

         i = 0;
     }

     int i;

};

Answer 1

For this, you need to understand what is static.

Static data members exist once for the entire class, as opposed to non-static data members, which exist individually in each instance of a class. They will have a class scope and does not bound to an instance of the class.

To access static member of the class, we use the format as below ::

if you have created 10 objects of a class. Assume, you were able to access the non-static variable in the static member of the class, When the static function is called, which object's member it needs to change?

Answer 2

It's not ok. Static functions are accessible without having an instance of a class and thus can't access information that you would need an instance to determine.

For example, you don't need a car to know how many wheels it has, blueprints for a general car would suffice (that could be static information) but you can't tell what color the car is unless you're referring to a specific car (that information needs a specific instance of an object.)