override specifier (C++11)

In a Nutshell

Adding override at the end of a virtual function declaration asks the compiler to verify that you really did override a base-class virtual function; a signature mismatch or a non-virtual base-class function becomes an immediate compile error.

Header

None (a language-keyword-level feature)

Core API Cheat Sheet

Operation	Signature	Description
Function declaration	return_type func_name(params) override;	Used at declaration time to ensure you are overriding a base-class virtual function
Function definition (in-class)	return_type func_name(params) override { ... }	Used when defining the function inside the class
Pure virtual override	return_type func_name(params) override = 0;	override appears before = 0
Combined with final	return_type func_name(params) override final;	Can be combined with final in either order
Destructor override	~Derived() override;	Can be used to check overrides of virtual destructors

Minimal Example

// Standard: C++11
#include <iostream>
struct Base { virtual void foo() { std::cout << "Base\n"; } };
struct Derived : Base {
    // void foo(int) override; // compile error: signature mismatch
    void foo() override { std::cout << "Derived\n"; }
};
int main() {
    Derived d;
    d.foo();
}

Embedded Applicability: High

• Zero runtime overhead; it is purely a compile-time static check
• Embedded code often has hardware abstraction layers (HALs) built on multi-level inheritance, and override effectively prevents the silent errors caused by modifications to a base-class interface
• No impact on code size or execution speed, a good fit for resource-sensitive contexts

Compiler Support

GCC	Clang	MSVC
4.7	3.0	2012

See Also

• cppreference: override specifier

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