Day 16 — override — cppinterview

Phần 1

1. What Problem Does It Solve?

override helps the compiler check that a function in a child class really replaces a virtual function from the parent class.

It catches mistakes such as:

Wrong function name
Wrong parameter type
Missing const

Phần 2

2. Minimal Syntax

class Animal {
public:
    virtual void talk();
};

class Cat : public Animal {
public:
    void talk() override;
};

Remember:

Parent class: virtual
Child class: override

Phần 3

3. Simple Example

class Animal {
public:
    virtual void talk() {
        cout << "Animal sound";
    }
};

class Cat : public Animal {
public:
    void talk() override {
        cout << "Meow";
    }
};

When an Animal pointer points to a Cat object:

Cat cat;
Animal* p = &cat;

p->talk();

Result:

Meow

Phần 4

4. Why Is override Useful?

Suppose the programmer writes the wrong function name:

void taak();

taak() does not replace talk().

With:

void taak() override;

the compiler reports an error immediately.

Phần 5

5. Common Mistake: Missing const

These two functions are different:

void talk() const;
void talk();

Correct code:

class Animal {
public:
    virtual void talk() const;
};

class Cat : public Animal {
public:
    void talk() const override;
};

Phần 6

6. Important Rules

The parent function must be virtual.
Write override in the child class.
The function names must match.
The parameters must match.
const must also match.
Use override whenever a child class replaces a virtual function.

Phần 7

7. Easy Mental Model

virtual  = allows replacing
override = checks replacing

override means:

Compiler, check that this child function really replaces a parent virtual function.

Mã mẫu hoàn chỉnh

cpp11/16_override/main.cpp

C++

#include <iostream>
using namespace std;

class Animal {
public:
    virtual void talk() {
        cout << "Animal\n";
    }
};

class Cat : public Animal {
public:
    void talk() override {
        cout << "Meow\n";
    }
};

int main() {
    Cat cat;
    Animal* p = &cat;

    p->talk();
}

Tự kiểm tra · không chấm điểm

Bạn đã hiểu những điểm nào?

Bài này chưa có danh sách tự kiểm tra trong nguồn.

#include <iostream> using namespace std; class Animal { public: virtual void talk() { cout << "Animal\n"; } }; class Cat : public Animal { public: void talk() override { cout << "Meow\n"; } }; int main() { Cat cat; Animal* p = &cat; p->talk(); }