C++ final specifier
C++ final specifier
Cast all your worries on him, because he cares for you. 1 Peter 5: 7 (Bible)In Java, we can use final for a function to make sure that it cannot be overridden. We can also use final in Java to make sure that a class cannot be inherited. Similarly, the latest C++ standard C++ 11 added final.
Use of final specifier in C++ 11:
Sometimes you don’t want to allow derived class to override the base class’ virtual function. C++ 11 allows built-in facility to prevent overriding of virtual function using final specifier.
Consider the following example which shows use of final specifier. This program fails in compilation.
#include <iostream> using namespace std; class Base { public: virtual void myfun() final { cout << "myfun() in Base"; } }; class Derived : public Base { void myfun() { cout << "myfun() in Derived\n"; } }; int main() { Derived d; Base &b = d; b.myfun(); return 0; }Output:
prog.cpp:14:10: error: virtual function ‘virtual void Derived::myfun()’ void myfun() ^ prog.cpp:7:18: error: overriding final function ‘virtual void Base::myfun()’ virtual void myfun() final2nd use of final specifier:
final specifier in C++ 11 can also be used to prevent inheritance of class / struct. If a class or struct is marked as final then it becomes non inheritable and it cannot be used as base class/struct.
The following program shows use of final specifier to make class non inheritable:
#include <iostream> class Base final { }; class Derived : public Base { }; int main() { Derived d; return 0; }Output:
error: cannot derive from ‘final’ base ‘Base’ in derived type ‘Derived’ class Derived : public Base
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