"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 and 64-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