What determines the size of an object here?

Question

I created a simple object containing integer and several methods, only an integer primitive variable and compare their sizes. "sizeof ()" for the return value of "4". Why is this - should not one object, which is a composite type and contains information about methods that take up more space?

#include <iostream>

class Person{

    private:
        int a;

    public:

        void hello(){
            std::cout << "hello";
        }

        void DoSomething(){
            a++;
        }
};

int main(){

    int a;
    Person p;

    std::cout << sizeof(a) << std::endl;

    std::cout << sizeof(p) << std::endl;

    return 0;
}

Answer 1

( - ++) "" . , . - , , . - Foo ,

return_type some_member_function(Foo* ptr, /* other params */){...}

, . ptr -,

foo.some_member_function(/* other params */)

some_member_function(&foo, /* other params */)

, ptr ++, this. this - prvalue, , -.

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PS: @greyfade, (-) virtual, " ". , . , , , .