Keywords (C++)

Keywords are predefined reserved identifiers that have special meanings. They can't be used as identifiers in your program. The following keywords are reserved for Microsoft C++. Names with leading underscores and names specified for C++/CX and C++/CLI are Microsoft extensions.

Standard C++ keywords

alignas
alignof
and ^b
and_eq ^b
asm ^a
auto
bitand ^b
bitor ^b
bool
break
case
catch
char
char8_t ^c
char16_t
char32_t
class
compl ^b
concept ^c
const
const_cast
consteval ^c
constexpr

constinit ^c
continue
co_await ^c
co_return ^c
co_yield ^c
decltype
default
delete
do
double
dynamic_cast
else
enum
explicit
export ^c
extern
false
float
for
friend
goto
if
inline

int
long
mutable
namespace
new
noexcept
not ^b
not_eq ^b
nullptr
operator
or ^b
or_eq ^b
private
protected
public
register reinterpret_cast
requires ^c
return
short
signed
sizeof
static
static_assert

static_cast
struct
switch
template
this
thread_local
throw
true
try
typedef
typeid
typename
union
unsigned
using declaration
using directive
virtual
void
volatile
wchar_t
while
xor ^b
xor_eq ^b

^a The Microsoft-specific __asm keyword replaces C++ asm syntax. asm is reserved for compatibility with other C++ implementations, but not implemented. Use __asm for inline assembly on x86 targets. Microsoft C++ doesn't support Inline assembly for other targets.

^b The extended operator synonyms are keywords when /permissive- or /Za (Disable language extensions) is specified. They aren't keywords when Microsoft extensions are enabled.

^c Supported when /std:c++20 or later (such as /std:c++latest) is specified.

Microsoft-specific C++ keywords

In C++, identifiers that contain two consecutive underscores are reserved for compiler implementations. The Microsoft convention is to precede Microsoft-specific keywords with double underscores. These words can't 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 /permissive- or /Za (Disable language extensions) option during compilation. These options disable some Microsoft-specific keywords.

When Microsoft extensions are enabled, you can use the Microsoft-specific keywords in your programs. For ANSI conformance, these keywords are prefaced by a double underscore. For backward compatibility, single-underscore versions of many of the double-underscored keywords are supported. The __cdecl keyword 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.

__alignof ^e
__asm ^e
__assume ^e
__based ^e
__cdecl ^e
__declspec ^e
__event
__except ^e
__fastcall ^e
__finally ^e
__forceinline ^e

__hook ^d
__if_exists
__if_not_exists
__inline ^e
__int16 ^e
__int32 ^e
__int64 ^e
__int8 ^e
__interface
__leave ^e
__m128

__m128d
__m128i
__m64
__multiple_inheritance ^e
__ptr32 ^e
__ptr64^e
__raise
__restrict ^e
__single_inheritance^e
__sptr^e
__stdcall ^e

__super
__thiscall
__unaligned ^e
__unhook ^d
__uptr ^e
__uuidof ^e
__vectorcall ^e
__virtual_inheritance ^e
__w64 ^e
__wchar_t

^d Intrinsic function used in event handling.

^e For backward compatibility with previous versions, these keywords are available both with two leading underscores and a single leading underscore when Microsoft extensions are enabled (the default).

Microsoft keywords in __declspec modifiers

These identifiers are extended attributes for the __declspec modifier. They're considered keywords within that context.

align
allocate
allocator
appdomain
code_seg
deprecated

dllexport
dllimport
jitintrinsic
naked
noalias
noinline

noreturn
no_sanitize_address
nothrow
novtable
process
property

restrict
safebuffers
selectany
spectre
thread
uuid

C++/CLI and C++/CX keywords

__abstract ^f
__box ^f
__delegate ^f
__gc ^f
__identifier
__nogc ^f
__noop
__pin ^f
__property ^f
__sealed ^f

__try_cast ^f
__value ^f
abstract ^g
array ^g
as_friend
delegate ^g
enum class
enum struct
event ^g

finally
for each in
gcnew ^g
generic ^g
initonly
interface class ^g
interface struct ^g
interior_ptr ^g
literal ^g

new ^g
property ^g
ref class
ref struct
safecast
sealed ^g
typeid
value class ^g
value struct ^g

^f Applicable to Managed Extensions for C++ only. This syntax is now deprecated. For more information, see Component Extensions for Runtime Platforms.

^g Applicable to C++/CLI.

See also

Lexical conventions
C++ built-in operators, precedence, and associativity