This is a list of reserved keywords in C. Since they are used by the language, these keywords are not available for re-definition.
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The most common keywords that begin with an underscore are generally used through their convenience macros:
keyword | used as | defined in |
_Alignas (since C11) | alignas | stdalign.h |
_Alignof (since C11) | alignof | stdalign.h |
_Atomic (since C11) | atomic_bool. atomic_int, ... | stdatomic.h |
_Bool (since C99) | bool | stdbool.h |
_Complex (since C99) | complex | complex.h |
_Generic (since C11) | (no macro) | |
_Imaginary (since C99) | imaginary | complex.h |
_Noreturn (since C11) | noreturn | stdnoreturn.h |
_Static_assert (since C11) | static_assert | assert.h |
_Thread_local (since C11) | thread_local | threads.h |
Also, each name that begins with a double underscore __ or an underscore followed by an uppercase letter is reserved: see identifier for details.
Note that digraphs <%
, %>
, <:
, :>
, %:
, and %:%:
provide an alternative way to represent standard tokens.
The following tokens are recognized by the preprocessor when they are used within the context of a preprocessor directive:
The following tokens are recognized by the preprocessor when they are used outside the context of a preprocessor directive:
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The following additional keywords are conditionally-supported:
References
- C11 standard (ISO/IEC 9899:2011):
- 6.4.1 Keywords (p: 58-59)
- C99 standard (ISO/IEC 9899:1999):
- 6.4.1 Keywords (p: 50)
- C89/C90 standard (ISO/IEC 9899:1990):
- 3.1.1 Keywords
See also
C++ documentation for C++ keywords |
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