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Q&A How to define an object with different subclasses in an if-statement?

What's going on is that the compiler is deciding on what function to call at compile time rather than runtime. Since the type of vh is Vehicle *, it is essentially creating this call: vh->Vehic...

posted 2y ago by Moshi‭

Answer
#1: Initial revision by user avatar Moshi‭ · 2023-02-05T02:08:44Z (almost 2 years ago)
What's going on is that the compiler is deciding on what function to call at compile time rather than runtime. Since the type of `vh` is `Vehicle *`, it is essentially creating this call:

```cpp
vh->Vehicle::print();
```

There are a couple of different solutions to this, but the simplest is probably just to make the function [virtual](https://en.cppreference.com/w/cpp/language/virtual). This says that the function should be determined at runtime instead. (This is usually accomplished through virtual tables.)

```cpp
class Vehicle
{
public:
	virtual void print(void)
	{
		std::cout << "this is a vehicle\n";
	}
};

class Car: public Vehicle
{
public:
	void print(void) override
	{
		std::cout << "this is a car\n";
	}
};

class Boat: public Vehicle
{
public:
	void print(void) override
	{
		std::cout << "this is a boat\n";
	}
};
```