C++ Keywords

Article
11/16/2012

Keywords are predefined reserved identifiers that have special meanings. They cannot be used as identifiers in your program. The following keywords are reserved for Microsoft C++. Names with leading underscores are Microsoft extensions.

__abstract 2	abstract	__alignof Operator	array
__asm	__assume	__based	bool
__box 2	break	case	catch
__cdecl	char	class	const
const_cast	continue	__declspec	default
__delegate 2	delegate	delete	deprecated 1
dllexport 1	dllimport 1	do	double
dynamic_cast	else	enum	enum class
enum struct	event	__event	__except
explicit	extern	false	__fastcall
__finally	finally	float	for
for each, in	__forceinline	friend	friend_as
__gc 2	gcnew	generic	goto
__hook 3	__identifier	if	__if_exists
__if_not_exists	initonly	__inline	inline
int	__int8	__int16	__int32
__int64	__interface	interface class	interface struct
interior_ptr	__leave	literal	long
__m64	__m128	__m128d	__m128i
__multiple_inheritance	mutable	naked 1	namespace
new	new	__nogc 2	noinline 1
__noop	noreturn 1	nothrow 1	novtable 1
nullptr	operator	__pin 2	private
__property 2	property	property 1	protected
public	__raise	ref struct	ref class
register	reinterpret_cast	return	safecast
__sealed 2	sealed	selectany 1	short
signed	__single_inheritance	sizeof	static
static_cast	__stdcall	struct	__super
switch	template	this	__thiscall
thread 1	throw	true	try
__try/__except, __try/__finally	__try_cast 2	typedef	typeid
typeid	typename	__unaligned	__unhook 3
union	unsigned	using declaration, using directive	uuid 1
__uuidof	value struct	value class	__value 2
virtual	__virtual_inheritance	void	volatile
__w64	__wchar_t, wchar_t	while

1 Extended attributes for the __declspec keyword.

2 Applicable to Managed Extensions for C++ only. This syntax is deprecated in Microsoft Visual C++ 2005.

3 Intrinsic function used in event handling.

See Language Features for Targeting the CLR for information on keywords that are new in Visual C++ 2005.

Microsoft Specific

In Microsoft C++, identifiers with two leading underscores are reserved for compiler implementations. Therefore, the Microsoft convention is to precede Microsoft-specific keywords with double underscores. These words cannot be used as identifier names.

Microsoft extensions are enabled by default. To ensure that your programs are fully portable, you can disable Microsoft extensions by specifying the ANSI-compatible /Za command-line option (compile for ANSI compatibility) during compilation. When you do this, Microsoft-specific keywords are disabled.

When Microsoft extensions are enabled, you can use the Microsoft-specific keywords in your programs. For ANSI compliance, these keywords are prefaced by a double underscore. For backward compatibility, single-underscore versions of all the double-underscored keywords except __except, __finally, __leave, and __try are supported. In addition, __cdecl is available with no leading underscore.

The __asm keyword replaces C++ asm syntax. asm is reserved for compatibility with other C++ implementations, but not implemented. Use __asm.

The __based keyword has limited uses for 32-bit and 64-bit target compilations.

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C++ Keywords

Microsoft Specific

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