Language Features for Targeting the CLR

Articolo
07/24/2011

This topic presents an overview of the syntax for writing applications to target the common language runtime.

The syntax is not part of the ISO/ANSI C++ standard but is a set of extensions to C++ standardized under the Ecma C++/CLI Standard.

This syntax replaces Managed Extensions for C++. Managed Extensions for C++ syntax is still available as a deprecated feature under the /clr:oldSyntax compiler option. To port code using Managed Extensions for C++, see Converting Managed Extensions for C++ Syntax.

This syntax is in effect by default when you use /clr.

For information on other features in Visual C++, see

CLR Data Type Keywords

The following table lists keywords that have been added to Visual C++. Note that some keywords consist of two words separated by white space. These aggregate keywords are considered keywords despite the fact that, used separately, they have different meanings. The word ref, for example, used without class is not a keyword and can be used as a regular identifier. Likewise, by itself class denotes a native class. But, used together, ref class defines a common language runtime (CLR) reference type.

Keyword	Context sensitive	Purpose	Reference
`ref class ref struct`	No	Defines a CLR reference class	Classes and Structs (Managed)
`value class value struct`	No	Defines a CLR value class	Classes and Structs (Managed)
`interface class interface struct`	No	Defines a CLR interface	interface class
`enum class enum struct`	No	Defines a CLR enumeration	enum class
`property`	Yes	Defines a CLR property	property
`delegate`	Yes	Defines a CLR delegate	delegate
`event`	Yes	Defines a CLR event	event (Visual C++)

Override Specifiers

The following keywords can be used to qualify override behavior for derivation. The new keyword is not new to C++ but is listed here because of the additional context in which it can be used. Some specifiers are also valid for native programming. For more information, see How to: Declare Override Specifiers in Native Compilations.

Keyword	Context Sensitive	Purpose	Reference
`abstract`	Yes	Indicates functions or classes are abstract	abstract (Visual C++)
`new`	No	Indicates that a function is not an override of a base class version	new (new slot in vtable)
`override`	Yes	Indicates that a method must be an override of a base-class version	override
`sealed`	Yes	Prevents classes from being used as base classes	sealed

Keywords for Generics

The following keywords have been added to support generic types. For more information, see Generics (Visual C++).

Keyword	Context sensitive	Purpose
`generic`	No	Defines a generic type
`where`	Yes	Specifies the constraints of a generic typef

Miscellaneous New Keywords

The following keywords have been added to Visual C++.

Keyword	Context sensitive	Purpose	Reference
`finally`	Yes	Indicates default exception handlings behavior	Exception Handling under /clr
`for each`	No	Enumerate elements of a collection.	for each, in
`gcnew`	No	Allocates types on the garbage-collected heap. Use instead of new and delete.	gcnew
`initonly`	Yes	Indicates a member can only be initialized at declaration or in a static constructor	initonly
`literal`	Yes	Creates a literal variable	literal (Visual C++)
`nullptr`	No	Indicates that a handle or pointer does not point at an object	nullptr

Non-Keyword Language Constructs

The following are language constructs that, while not official keywords, are fundamental to .NET programming. These constructs are implemented as templates. Most are defined in the cli Namespace.

Keyword	Purpose	Reference
`array`	Type for representing CLR arrays	array (Visual C++)
`interior_ptr`	Points to data inside reference types.	interior_ptr
`pin_ptr`	Points to CLR reference types to temporarily suppress the garbage collection system	pin_ptr
`safe_cast`	Determines and executes the optimal casting method for CLR types	safe_cast
`typeid`	Retrieves a System.Type object describing the given type or object	typeid

Operators

Two operators have been added to Visual C++ to support garbage-collected programming.

Operator	Purpose	Reference
`^`	Indicates a handle to an object located on the garbage-collected heap	^ (Handle to Object on Managed Heap)
`%`	Indicates a tracking reference	% (Tracking Reference)

More CLR Constructs

In addition to keywords and language constructs, this reference section includes the following CLR programming constructs.

Topic	Description
__identifier	Enables the use of keywords as identifiers
... (Variable Argument Lists)	Enables a function to take a variable number of arguments.
.NET Framework Equivalents to C++ Native Types (C++/CLI)	Lists the CLR types used in place of C++ integral types
appdomain __declspec modifier	__declspec modifier that mandates static and global variables exist per appdomain
C-Style Casts with /clr	Describes how C-style casts are interpreted
__clrcall calling convention	Indicates the CLR-compliant calling convention
__cplusplus_cli	Predefined Macros
Custom Attributes (C++)	Describes how to define your own CLR attributes.
Exception Handling under /clr	Provides an overview of exception handling
Explicit Overrides	Demonstrates how member functions can override arbitrary members
Friend Assemblies (C++)	Discusses how a client assembly can access all types in an assembly component.
Implicit Boxing	Demonstrates the conditions where values types are boxed
Compiler Support for Type Traits	Discusses how to detect characteristics of types at compile time.
managed, unmanaged pragmas	Demonstrates how managed and unmanaged functions can co-exist in the same module
process __declspec modifier	__declspec modifier that mandates static and global variables exist per process
Reflection (C++/CLI)	Demonstrates the CLR version of run-time type information
System::String Handling in Visual C++	Discusses compiler conversion of string literals to String.
Type Forwarding	Allows you to move a type in a shipping assembly to another assembly, such that, client code does not have to be recompiled.
User-Defined Attributes	Demonstrates use-defined attributes
#using Directive (C/C++)	Imports external assemblies
XML Documentation (Visual C++)	Explains XML-based code documentation using /doc (Process Documentation Comments) (C/C++)

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