Why can't a static member function have a const qualifier?

In C++, static member functions are defined at the class level rather than tied to specific instances. This means they do not depend on particular class objects, as they operate on no object data members. Consequently, static member functions lack a this pointer, which would otherwise reference a class instance.

The const qualifier for member functions is primarily used to indicate that the function does not modify the object's state (i.e., it does not alter any non-static data members). Because static member functions inherently cannot access non-static data members, adding the const qualifier is redundant and inconsistent with the language's design principles.

For example, consider a class Calculator that includes both a static member function and a non-static member function:

cpp
class Calculator {
public:
    static int add(int a, int b) {
        return a + b;
    }

    int multiply(int a, int b) const {
        return a * b;
    }
};

In this example, the add function is static, processing only the provided parameters without relying on any Calculator instances. Attempting to declare it as const triggers a compiler error, as static member functions do not interact with class instance state.

The multiply function is non-static and uses the const qualifier, signifying it does not modify any class member variables (though in this specific case, it does not alter anything). This is highly valuable for member functions that need to access class instance data without modification.

To summarize, static member functions cannot be declared with the const qualifier because they are not associated with specific class instances, and there is no object state to protect with const.