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Component Extensions for Runtime Platforms


The latest version of this topic can be found at Component Extensions for Runtime Platforms.

Visual C++ provides language extensions to help you program against runtime platforms. By using Visual C++ component extensions (C++/CX), you can program Windows 8.x Store apps and components that compile to native code. Although you can create Windows 8.x Store apps by programming directly against the Windows Runtime COM interfaces, by using C++/CX, you can work with constructors, exceptions, and other modern C++ programming idioms. To enable C++ programming in a managed execution environment on the .NET platform, you can use C++/CLI.

Two runtimes, one set of extensions

C++/CX is a subset of C++/CLI. For extensions that are common to C++/CX and C++/CLI, the semantics depend on whether you are targeting the common language runtime (CLR) or the Windows Runtime. To compile your app to run on the Windows Runtime, specify the /ZW compiler option. To compile it to run on the CLR, specify the /clr compiler option. These switches are set automatically when you use Visual Studio to create a project.

For more information about how to create Windows 8.x Store apps in C++, see Roadmap for Windows Runtime apps using C++.

C++/CLI extends the ISO/ANSI C++ standard, and is defined under the Ecma C++/CLI Standard. For more information, see .NET Programming with C++/CLI (Visual C++).

The language extensions include aggregate keywords, which are keywords that consist of two tokens separated by white space. The tokens might have one meaning when they are used separately, and another meaning when they are used together. For example, the word "ref" is an ordinary identifier, and the word "class" is a keyword that declares a native class. But when these words are combined to form ref class, the resulting aggregate keyword declares an entity that is known as a runtime class.

The extensions also include context-sensitive keywords. A keyword is treated as context-sensitive depending on the kind of statement that contains it, and its placement in that statement. For example, the token "property" can be an identifier, or it can declare a special kind of public class member.

The following table lists keywords in the C++ language extension.

KeywordContext sensitivePurposeReference
ref class

 ref struct
NoDeclares a class.Classes and Structs
value class

 value struct
NoDeclares a value class.Classes and Structs
interface class

 interface struct
NoDeclares an interface.interface class
enum class

 enum struct
NoDeclares an enumeration.enum class
propertyYesDeclares a
delegateYesDeclares a delegate.delegate (C++ Component Extensions)
eventYesDeclares an event.event

You can use the following keywords to qualify override behavior for derivation. Although the new keyword is not an extension of C++, it is listed here because it can be used in an additional context. Some specifiers are also valid for native programming. For more information, see How to: Declare Override Specifiers in Native Compilations (C++/CLI).

KeywordContext SensitivePurposeReference
abstractYesIndicates that functions or classes are abstract.abstract
newNoIndicates that a function is not an override of a base class (new slot in vtable)
overrideYesIndicates that a method must be an override of a base-class version.override
sealedYesPrevents classes from being used as base classes.sealed

The following keywords have been added to support generic types. For more information, see Generics.

KeywordContext sensitivePurpose
genericNoDeclares a generic type.
whereYesSpecifies the constraints that are applied to a generic type parameter.

The following keywords have been added to the C++ extensions.

KeywordContext sensitivePurposeReference
finallyYesIndicates default exception handlings behavior.Exception Handling
for each, inNoEnumerates elements of a collection.for each, in
gcnewNoAllocates types on the garbage-collected heap. Use instead of new and delete.ref new, gcnew
ref newYesAllocates a Windows Runtime type. Use instead of new and delete.ref new, gcnew
initonlyYesIndicates that a member can only be initialized at declaration or in a static constructor.initonly (C++/CLI)
literalYesCreates a literal variable.literal
nullptrNoIndicates that a handle or pointer does not point at an object.nullptr

The following language constructs are implemented as templates, instead of as keywords. If you specify the /ZW compiler option, they are defined in the lang namespace. If you specify the /clr compiler option, they are defined in the cli namespace.

arrayDeclares an array.Arrays
interior_ptr(CLR only) Points to data in a reference type.interior_ptr (C++/CLI)
pin_ptr(CLR only) Points to CLR reference types to temporarily suppress the garbage-collection system.pin_ptr (C++/CLI)
safe_castDetermines and executes the optimal casting method for a runtime type.safe_cast
typeid(CLR only) Retrieves a System.Type object that describes the given type or object.typeid

The following type declarators instruct the runtime to automatically manage the lifetime and deletion of allocated objects.

^Declares a handle to an object; that is, a pointer to a Windows Runtime or CLR object that is automatically deleted when it is no longer usable.Handle to Object Operator (^)
%Declares a tracking reference; that is, a reference to a Windows Runtime or CLR object that is automatically deleted when it is no longer usable.Tracking Reference Operator

This section lists additional programming constructs, and topics that pertain to the CLR.

__identifier (C++/CLI)(Windows Runtime and CLR) Enables the use of keywords as identifiers.
Variable Argument Lists (...) (C++/CLI)(Windows Runtime and CLR) Enables a function to take a variable number of arguments.
.NET Framework Equivalents to C++ Native Types (C++/CLI)Lists the CLR types that are used in place of C++ integral types.
appdomain __declspec modifier__declspec modifier that mandates that static and global variables exist per appdomain.
C-Style Casts with /clr (C++/CLI)Describes how C-style casts are interpreted.
__clrcall calling conventionIndicates the CLR-compliant calling convention.
__cplusplus_cliPredefined Macros
Custom AttributesDescribes how to define your own CLR attributes.
Exception HandlingProvides an overview of exception handling.
Explicit OverridesDemonstrates how member functions can override arbitrary members.
Friend Assemblies (C++)Discusses how a client assembly can access all types in an assembly component.
BoxingDemonstrates the conditions in which values types are boxed.
Compiler Support for Type TraitsDiscusses how to detect characteristics of types at compile time.
managed, unmanaged pragmasDemonstrates how managed and unmanaged functions can co-exist in the same module.
process __declspec modifier__declspec modifier that mandates that static and global variables exist per process.
Reflection (C++/CLI)Demonstrates the CLR version of run-time type information.
StringDiscusses compiler conversion of string literals to String.
Type Forwarding (C++/CLI)Enables the movement of a type in a shipping assembly to another assembly so that client code does not have to be recompiled.
User-Defined AttributesDemonstrates user-defined attributes.
#using DirectiveImports external assemblies.
XML DocumentationExplains XML-based code documentation by using /doc (Process Documentation Comments) (C/C++)

.NET Programming with C++/CLI (Visual C++)
Native and .NET Interoperability