Difference between static and constant function in C++

Static Function: It is a member function that is used to access only static data members. It cannot access non-static data members not even call non-static member functions. It can be called even if no objects of the class exist. It is also used to maintain a single copy of the class member function across different objects of the class.

Program 1:

C++

// C++ program to illustrate the use
// of static function
#include "bits/stdc++.h"
using namespace std;

class A {
public:
    static void f()
    {
        cout << "GeeksforGeeks!";
    }
};

// Driver Code
int main()
{
    A::f();
}

Output:

GeeksforGeeks!

Constant Function: It is a function that is generally declared as constant in the program. It also guarantees that it will not allow modifying objects or call any non-const member functions. It specifies that function is a read-only function and does not modify the object for which it is called.  

Program 2:

C++

// C++ program to illustrate the use
// of const keyword

#include <iostream>
using namespace std;

// Driver Code
int main()
{
    const double a = 1;

    // Using the below line of code
    // gives error
    // a = 2.21;

    cout << a << endl;

    return 0;
}

Output:

1

Tabular Difference between static function and constant function:  

Static Function	Constant Function
It is declared using the static keyword.	It is declared using the const keyword.
It does not allow variable or data members or functions to be modified again. Instead, it is allocated for a lifetime of the program.	It allows specifying whether a variable is modifiable or not.
It helps to call functions that using class without using objects.	It helps us to avoid modifying objects.
This function can only be called by static data members and static member functions.	This function can be called using any type of object.
It is useful to declare global data which should be updated while the program lives in memory, used to restrict access to functions, reuse the same function name in other files, etc.	It is useful with pointers or references passed to function, used to avoid accidental changes to object, can be called by any type of object, etc.
It is a member function that generally allows accessing function using class without using an instance of the class.	It is a member function that is generally declared as constant in the program.