virtual_class_ptr.cpp

#include <cstdio>

class A {
    public:
        int x;

        A(int x): x(x) {}
};

class B: public A {
    public:
        B(int x): A(x) {}

        virtual void f();
};

void B::f() {}

void dump_bytes(const void *ptr, int n = 12) {
    const unsigned char *bytes = (const unsigned char*)ptr;
    for (int i = 0; i < n; i++)
        printf("%02x ", bytes[i]);
    printf("\n");
}

int main() {
    A a(5);
    printf("&a:  ");
    dump_bytes(&a);     // &a:  05 00 00 00 a0 99 4f 68 b4 7f 00 00

    B b(5);
    printf("&b:  ");
    dump_bytes(&b);     // &b:  68 ad 23 4d a0 55 00 00 05 00 00 00

    printf("\n");

    A *pb = &b;
    printf("pb->x = %d\n", pb->x);      // 5
    A *rpb = reinterpret_cast<A*>(&b);
    printf("rpb->x = %d\n", rpb->x);    // 1294183784

    printf("\n");

    printf("&b = %p\n", &b);                        // 0x7fffe0703e10
    printf("(u8*)&b = %p\n", (unsigned char*)&b);   // 0x7fffe0703e10
    printf("(A*)&b = %p\n", (A*)&b);                // 0x7fffe0703e18
    printf("reinterpret_cast<A*>(&b) = %p\n", reinterpret_cast<A*>(&b));    // 0x7fffe0703e10
}