virtual
Syntax:
virtual return-type name( parameter-list ); virtual return-type name( parameter-list ) = 0;
The virtual keyword can be used to create virtual functions, which can be overridden by derived classes.
- A virtual function indicates that a function can be overridden in a subclass, and that the overridden function will actually be used.
- When a base object pointer points to a derived object that contains a virtual function, the decision about which version of that function to call is based on the type of object pointed to by the pointer, and this process happens at runtime.
- A base object can point to different derived objects and have different versions of the virtual function run.
If the function is specified as a pure virtual function (denoted by the = 0), it must be overridden by a derived class.
Example code:
For example, the following code snippet shows how a child class can override a virtual method of its parent, and how a non-virtual method in the parent cannot be overridden:
class Base {
public:
void nonVirtualFunc() {
cout << "Base: non-virtual function" << endl;
}
virtual void virtualFunc() {
cout << "Base: virtual function" << endl;
}
};
class Child : public Base {
public:
void nonVirtualFunc() {
cout << "Child: non-virtual function" << endl;
}
void virtualFunc() {
cout << "Child: virtual function" << endl;
}
};
int main() {
Base* basePointer = new Child();
basePointer->nonVirtualFunc();
basePointer->virtualFunc();
return 0;
}
When run, the above code displays:
Base: non-virtual function Child: virtual function
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