---
title: "interface class  (C++/CLI and C++/CX)"
ms.date: "10/12/2018"
ms.topic: "reference"
f1_keywords: ["interface_CPP"]
helpviewer_keywords: ["interface class keyword", "interface struct keyword"]
ms.assetid: 3ccea701-f50b-4da7-ad6b-f0ee1203e2b9
---
# interface class  (C++/CLI and C++/CX)

Declares an interface.  For information on native interfaces, see [__interface](../cpp/interface.md).

## All Runtimes

### Syntax

```cpp
interface_access
interface class
name :  inherit_accessbase_interface{};interface_accessinterface structname :  inherit_accessbase_interface{};
```

### Parameters

*interface_access*<br/>
The accessibility of an interface outside the assembly.  Possible values are **public** and **private**.  **private** is the default. Nested interfaces cannot have an *interface_access* specifier.

*name*<br/>
The name of the interface.

*inherit_access*<br/>
The accessibility of *base_interface*.  The only permitted accessibility for a base interface is **public** (the default).

*base_interface*<br/>
(Optional) A base interface for interface *name*.

### Remarks

**interface struct** is equivalent to **interface class**.

An interface can contain declarations for functions, events, and properties.  All interface members have public accessibility. An interface can also contain static data members, functions, events, and properties, and these static members must be defined in the interface.

An interface defines how a class may be implemented. An interface is not a class and classes can only implement interfaces. When a class defines a function declared in an interface, the function is implemented, not overridden. Therefore, name lookup does not include interface members.

A class or struct that derives from an interface must implement all members of the interface. When implementing interface *name* you must also implement the interfaces in the `base_interface` list.

For more information, see:

- [Interface Static Constructor](../dotnet/how-to-define-an-interface-static-constructor-cpp-cli.md)

- [Generic Interfaces (C++/CLI)](generic-interfaces-visual-cpp.md)

For information on other CLR types, see [Classes and Structs](classes-and-structs-cpp-component-extensions.md).

You can detect at compile time if a type is an interface with `__is_interface_class(type)`. For more information, see [Compiler Support for Type Traits](compiler-support-for-type-traits-cpp-component-extensions.md).

In the development environment, you can get F1 help on these keywords by highlighting the keyword, (`interface class`, for example) and pressing F1.

## Windows Runtime

### Remarks

(There are no remarks for this language feature that apply to only the Windows Runtime.)

### Requirements

Compiler option: `/ZW`

## Common Language Runtime

### Remarks

(There are no remarks for this language feature that apply to only the common language runtime.)

### Requirements

Compiler option: `/clr`

### Examples

The following code example demonstrates how an interface can define the behavior of a clock function.

```cpp
// mcppv2_interface_class.cpp
// compile with: /clr
using namespace System;

public delegate void ClickEventHandler(int, double);

// define interface with nested interface
public interface class Interface_A {
   void Function_1();

   interface class Interface_Nested_A {
      void Function_2();
   };
};

// interface with a base interface
public interface class Interface_B : Interface_A {
   property int Property_Block;
   event ClickEventHandler^ OnClick;
   static void Function_3() { Console::WriteLine("in Function_3"); }
};

// implement nested interface
public ref class MyClass : public Interface_A::Interface_Nested_A {
public:
   virtual void Function_2() { Console::WriteLine("in Function_2"); }
};

// implement interface and base interface
public ref class MyClass2 : public Interface_B {
private:
   int MyInt;

public:
   // implement non-static function
   virtual void Function_1() { Console::WriteLine("in Function_1"); }

   // implement property
   property int Property_Block {
      virtual int get() { return MyInt; }
      virtual void set(int value) { MyInt = value; }
   }
   // implement event
   virtual event ClickEventHandler^ OnClick;

   void FireEvents() {
      OnClick(7, 3.14159);
   }
};

// class that defines method called when event occurs
ref class EventReceiver {
public:
   void OnMyClick(int i, double d) {
      Console::WriteLine("OnClick: {0}, {1}", i, d);
   }
};

int main() {
   // call static function in an interface
   Interface_B::Function_3();

   // instantiate class that implements nested interface
   MyClass ^ x = gcnew MyClass;
   x->Function_2();

   // instantiate class that implements interface with base interface
   MyClass2 ^ y = gcnew MyClass2;
   y->Function_1();
   y->Property_Block = 8;
   Console::WriteLine(y->Property_Block);

   EventReceiver^ MyEventReceiver = gcnew EventReceiver();

   // hook handler to event
   y->OnClick += gcnew ClickEventHandler(MyEventReceiver, &EventReceiver::OnMyClick);

   // invoke events
   y->FireEvents();

   // unhook handler to event
   y->OnClick -= gcnew ClickEventHandler(MyEventReceiver, &EventReceiver::OnMyClick);

   // call implemented function via interface handle
   Interface_A^ hi = gcnew MyClass2();
   hi->Function_1();
}
```

```Output
in Function_3

in Function_2

in Function_1

8

OnClick: 7, 3.14159

in Function_1
```

The following code sample shows two ways to implement functions with the same signature declared in multiple interfaces and where those interfaces are used by a class.

```cpp
// mcppv2_interface_class_2.cpp
// compile with: /clr /c
interface class I {
   void Test();
   void Test2();
};

interface class J : I {
   void Test();
   void Test2();
};

ref struct R : I, J {
   // satisfies the requirement to implement Test in both interfaces
   virtual void Test() {}

   // implement both interface functions with explicit overrides
   virtual void A() = I::Test2 {}
   virtual void B() = J::Test2 {}
};
```

## See also

[Component Extensions for .NET and UWP](component-extensions-for-runtime-platforms.md)