What is the private virtual method in C++

In C language, conceptually there is no "private virtual method" because it is a concept in object-oriented programming (OOP), and C is a procedural programming language that does not support features like classes and virtual functions.

However, we can simulate similar object-oriented behavior in C using techniques such as structs to simulate objects and function pointers within structs to simulate virtual methods. For "private," in C, we can limit its visibility outside the file where it is defined by declaring the function as static, achieving a similar effect to private methods in object-oriented programming.

Example:

Suppose we want to simulate a simple "Animal" class in C, which has a virtual method called makeSound, but we want this method to be uncallable outside the struct, i.e., behave as a "private" method.

First, define an Animal struct and a corresponding function pointer type:

c
typedef struct Animal Animal;

typedef void (*MakeSoundFunc)(Animal *);

struct Animal {
    MakeSoundFunc makeSound;
};

Then define a static function to implement this virtual method. Since this function is static, it is not visible outside the file where it is defined:

c
static void animalMakeSound(Animal *self) {
    printf("Some generic animal sound\n");
}

Now, we can create and initialize an instance of the "Animal" type within the file, and call this method indirectly through a pointer:

c
void initAnimal(Animal *animal) {
    animal->makeSound = animalMakeSound;
}

int main() {
    Animal myAnimal;
    initAnimal(&myAnimal);
    myAnimal.makeSound(&myAnimal);  // Call the virtual method, output: "Some generic animal sound"
    return 0;
}

In this example, we successfully simulate an object-oriented pattern with virtual functionality using structs and function pointers. Meanwhile, the animalMakeSound function, being static, is not visible outside the module, achieving a similar effect to a private method.