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C Keywords

"Keywords" are words that have special meaning to the C compiler. In translation phases 7 and 8, an identifier cannot have the same spelling and case as a C keyword. (See a description of translation phases in the Preprocessor Reference; for information on identifiers, see Identifiers.) The C language uses the following keywords:

auto

double

int

struct

break

else

long

switch

case

enum

register

typedef

char

extern

return

union

const

float

short

unsigned

continue

for

signed

void

default

goto

sizeof

volatile

do

if

static

while

You cannot redefine keywords. However, you can specify text to be substituted for keywords before compilation by using C preprocessor directives.

Microsoft Specific

The ANSI C standard allows identifiers with two leading underscores to be reserved for compiler implementations. Therefore, the Microsoft convention is to precede Microsoft-specific keyword names with double underscores. These words cannot be used as identifier names. For a description of the ANSI rules for naming identifiers, including the use of double underscores, see Identifiers.

The following keywords and special identifiers are recognized by the Microsoft C compiler:

__asm

dllimport2

__int8

naked2

__based1

__except

__int16

__stdcall

__cdecl

__fastcall

__int32

thread2

__declspec

__finally

__int64

__try

dllexport2

__inline

__leave

 

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

2. These are special identifiers when used with __declspec; their use in other contexts is not restricted.

Microsoft extensions are enabled by default. To ensure that your programs are fully portable, you can disable Microsoft extensions by specifying the /Za 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 keywords listed above in your programs. For ANSI compliance, most of these keywords are prefaced by a double underscore. The four exceptions, dllexport, dllimport, naked, and thread, are used only with __declspec and therefore do not require a leading double underscore. For backward compatibility, single-underscore versions of the rest of the keywords are supported.

END Microsoft Specific

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