What is the difference between a static and const variable?

Question

Can someone explain the difference between a static and const variable?

Answer 1

static

is used for making the variable a class variable. You need not define a static variable while declaring.

Example:

#include 

class dummy
{
        public:
                static int dum;
};


int dummy::dum = 0; //This is important for static variable, otherwise you'd get a linking error

int main()
{
        dummy d;
        d.dum = 1;

        std::cout<<"Printing dum from object: "<

This would print: Printing dum from object: 1 Printing dum from class: 1

The variable dum is a class variable. Trying to access it via an object just informs the compiler that it is a variable of which class. Consider a scenario where you could use a variable to count the number of objects created. static would come in handy there.

const

is used to make it a read-only variable. You need to define and declare the const variable at once.

In the same program mentioned above, let's make the dum a const as well:

class dummy
{
        public:
                static const int dum; // This would give an error. You need to define it as well
                static const int dum = 1; //this is correct
                const int dum = 1; //Correct. Just not making it a class variable

};

Suppose in the main, I am doing this:

int main()
{
        dummy d;
        d.dum = 1; //Illegal!

        std::cout<<"Printing dum from object: "<

Though static has been manageable to understand, const is messed up in c++. The following resource helps in understanding it better: http://duramecho.com/ComputerInformation/WhyHowCppConst.html