Explicit Overrides (C++ Component Extensions)
The latest version of this topic can be found at Explicit Overrides (C++ Component Extensions).
This topic discusses how to explicitly override a member of a base class or interface. A named (explicit) override should only be used to override a method with a derived method that has a different name.
All Runtimes
Syntax
overriding-function-declarator = type::function [,type::function] { overriding-function-definition }
overriding-function-declarator = function { overriding-function-definition }
Parameters
overriding-function-declarator
The return type, name, and argument list of the overriding function. Note that the overriding function does not have to have the same name as the function being overridden.
type
The base type that contains a function to override.
function
A comma-delimited list of one or more function names to override.
overriding-function-definition
The function body statements that define the overriding function.
Remarks
Use explicit overrides to create an alias for a method signature, or to provide different implementations for methods witht the same signature.
For information about modifying the behavior of inherited types and inherited type members, see Override Specifiers.
Windows Runtime
Requirements
Compiler option: /ZW
Common Language Runtime
Remarks
For information about explicit overrides in native code or code compiled with /clr:oldSyntax, see Explicit Overrides.
Requirements
Compiler option: /clr
Examples
Example
The following code example shows a simple, implicit override and implementation of a member in a base interface, not using explicit overrides.
// explicit_override_1.cpp
// compile with: /clr
interface struct I1 {
virtual void f();
};
ref class X : public I1 {
public:
virtual void f() {
System::Console::WriteLine("X::f override of I1::f");
}
};
int main() {
I1 ^ MyI = gcnew X;
MyI -> f();
}
Output
X::f override of I1::f
Example
The following code example shows how to implement all interface members with a common signature, using explicit override syntax.
// explicit_override_2.cpp
// compile with: /clr
interface struct I1 {
virtual void f();
};
interface struct I2 {
virtual void f();
};
ref struct X : public I1, I2 {
virtual void f() = I1::f, I2::f {
System::Console::WriteLine("X::f override of I1::f and I2::f");
}
};
int main() {
I1 ^ MyI = gcnew X;
I2 ^ MyI2 = gcnew X;
MyI -> f();
MyI2 -> f();
}
Output
X::f override of I1::f and I2::f
X::f override of I1::f and I2::f
Example
The following code example shows how a function override can have a different name from the function it is implementing.
// explicit_override_3.cpp
// compile with: /clr
interface struct I1 {
virtual void f();
};
ref class X : public I1 {
public:
virtual void g() = I1::f {
System::Console::WriteLine("X::g");
}
};
int main() {
I1 ^ a = gcnew X;
a->f();
}
Output
X::g
Example
The following code example shows an explicit interface implementation that implements a type safe collection.
// explicit_override_4.cpp
// compile with: /clr /LD
using namespace System;
ref class R : ICloneable {
int X;
virtual Object^ C() sealed = ICloneable::Clone {
return this->Clone();
}
public:
R() : X(0) {}
R(int x) : X(x) {}
virtual R^ Clone() {
R^ r = gcnew R;
r->X = this->X;
return r;
}
};