JuniorTheoryCommon

What does the program print?

C++

#include <iostream>

struct Shape {
    virtual int sides() const { return 0; }
};
struct Circle : public Shape {};
struct Square : public Shape {};
int main() {
    Square sq;
    Shape* p = &sq;
    std::cout << (dynamic_cast<Circle*>(p) == nullptr) << '\n';
}

Expecting 0: dynamic_cast checks the real type of the object at run time, and p points to a Square, not a Circle, so the result is nullptr.
Expecting undefined behavior: dynamic_cast never converts to a wrong type; when the object does not match, dynamic_cast returns nullptr instead.

What would dynamic_cast<Square*>(p) return here?
Why does this dynamic_cast stop compiling if sides is not virtual?

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JuniorTheoryCommon

What does the program print?

C++

#include <iostream>

struct Shape {
    virtual int sides() const { return 0; }
};
struct Circle : public Shape {};
struct Square : public Shape {};
int main() {
    Square sq;
    Shape* p = &sq;
    std::cout << (dynamic_cast<Circle*>(p) == nullptr) << '\n';
}

Expecting 0: dynamic_cast checks the real type of the object at run time, and p points to a Square, not a Circle, so the result is nullptr.
Expecting undefined behavior: dynamic_cast never converts to a wrong type; when the object does not match, dynamic_cast returns nullptr instead.

What would dynamic_cast<Square*>(p) return here?
Why does this dynamic_cast stop compiling if sides is not virtual?

Back to questions Open topic in roadmap →Answer it yourself — Quiz