“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