22. Preprocessing Directives

# if
# ifdef
# ifndef
# elif
# else
# endif
# include
# define
# undef
# line
# error
# pragma

Operators:

defined, _Pragma, #, ##

Predefined macro names:

__DATE__, __FILE__, __LINE__, __STDC__, __STDC_HOSTED__, __STDC_VERSION__, __TIME__

__STDC_ISO_10646__, __STDC_MB_MIGHT_NEQ_WC__, __STDC_UTF_16__, __STDC_UTF_32__, __STDC_ANALYZABLE__, __STDC_IEC_559__, __STDC_IEC_559_COMPLEX__, __STDC_LIB_EXT1__, __STDC_NO_ATOMICS__, __STDC_NO_COMPLEX__, __STDC_NO_THREADS__, __STDC_NO_VLA__

__VA_ARGS__

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C17 (pdf) - 6.10 Preprocessing directives

See also cppreference.com/w/c/preprocessor