C lexical grammar

Tokens

token:
 keyword
 identifier
 constant
 string-literal
 punctuator

preprocessing-token:
 header-name
 identifier
 pp-number
 character-constant
 string-literal
 punctuator
 each non-whitespace character that can't be one of the above

Keywords

keyword: one of
 auto break case char const continue
 default do double else enum extern
 float for goto if inline int long
 register restrict return short signed
 sizeof static struct switch typedef union
 unsigned void volatile while _Alignas
 _Alignof _Atomic _Bool _Complex _Generic
 _Imaginary _Noreturn _Static_assert
 _Thread_local

For a list of additional Microsoft-specific keywords, see C keywords.

Identifiers

identifier:
 identifier-nondigit
 identifier identifier-nondigit
 identifier digit

identifier-nondigit:
 nondigit
 universal-character-name
 other implementation-defined characters

nondigit: one of
 _ a b c d e f g h i j k l m
 n o p q r s t u v w x y z
 A B C D E F G H I J K L M
 N O P Q R S T U V W X Y Z

digit: one of
 0 1 2 3 4 5 6 7 8 9

universal-character-name:
 \u hex-quad
 \U hex-quad hex-quad

hex-quad:
 hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit

Constants

constant:
 integer-constant
 floating-constant
 enumeration-constant
 character-constant

integer-constant:
 decimal-constant integer-suffix_opt
 binary-constant¹ integer-suffix_opt
 octal-constant integer-suffix_opt
 hexadecimal-constant integer-suffix_opt

decimal-constant:
 nonzero-digit
 decimal-constant digit

binary-constant:¹
 binary-prefix binary-digit
 binary-constant binary-digit

binary-prefix¹: one of
 0b 0B

binary-digit¹: one of
 0 1

octal-constant:
 0
 octal-constant octal-digit

hexadecimal-constant:
 hexadecimal-prefix hexadecimal-digit
 hexadecimal-constant hexadecimal-digit

hexadecimal-prefix: one of
 0x 0X

nonzero-digit: one of
 1 2 3 4 5 6 7 8 9

octal-digit: one of
 0 1 2 3 4 5 6 7

hexadecimal-digit: one of
 0 1 2 3 4 5 6 7 8 9
 a b c d e f
 A B C D E F

integer-suffix:
 unsigned-suffix long-suffix_opt
 unsigned-suffix long-long-suffix_opt
 long-suffix unsigned-suffix_opt
 long-long-suffix unsigned-suffix_opt

unsigned-suffix: one of
 u U

long-suffix: one of
 l L

long-long-suffix: one of
 ll LL

floating-constant:
 decimal-floating-constant
 hexadecimal-floating-constant

decimal-floating-constant:
 fractional-constant exponent-part_opt floating-suffix_opt
 digit-sequence exponent-part floating-suffix_opt

hexadecimal-floating-constant:
 hexadecimal-prefix hexadecimal-fractional-constant binary-exponent-part_opt floating-suffix_opt
 hexadecimal-prefix hexadecimal-digit-sequence binary-exponent-part floating-suffix_opt

fractional-constant:
 digit-sequence_opt . digit-sequence
 digit-sequence .

exponent-part:
 e sign_opt digit-sequence
 E sign_opt digit-sequence

sign: one of
 + -

digit-sequence:
 digit
 digit-sequence digit

hexadecimal-fractional-constant:
 hexadecimal-digit-sequence_opt . hexadecimal-digit-sequence
 hexadecimal-digit-sequence .

binary-exponent-part:
 p sign_opt digit-sequence
 P sign_opt digit-sequence

hexadecimal-digit-sequence:
 hexadecimal-digit
 hexadecimal-digit-sequence hexadecimal-digit

floating-suffix: one of
 f l F L

enumeration-constant:
 identifier

character-constant:
 ' c-char-sequence '
 L' c-char-sequence '

c-char-sequence:
 c-char
 c-char-sequence c-char

c-char:
 Any member of the source character set except the single quotation mark ('), backslash (\), or new-line character
 escape-sequence

escape-sequence:
 simple-escape-sequence
 octal-escape-sequence
 hexadecimal-escape-sequence
 universal-character-name

simple-escape-sequence: one of
 \a \b \f \n \r \t \v
 \' \" \\ \?

octal-escape-sequence:
 \ octal-digit
 \ octal-digit octal-digit
 \ octal-digit octal-digit octal-digit

hexadecimal-escape-sequence:
 \x hexadecimal-digit
 hexadecimal-escape-sequence hexadecimal-digit

String literals

string-literal:
 encoding-prefix " s-char-sequence_opt "

encoding-prefix:
 u8
 u
 U
 L

s-char-sequence:
 s-char
 s-char-sequence s-char

s-char:
 any member of the source character set except the double-quotation mark ("), backslash (\), or new-line character
 escape-sequence

Punctuators

punctuator: one of
 [ ] ( ) { } . ->
 ++ -- & * + - ~ !
 / % << >> < > <= >= ==
 != ^ | && || ? : ; ...
 = *= /= %= += -= <<= >>=
 &= ^= |= , # ##
 <: :> <% %> %: %:%:

Header names

header-name:
 < h-char-sequence >
 " q-char-sequence "

h-char-sequence:
 h-char
 h-char-sequence h-char

h-char:
 any member of the source character set except the new-line character and >

q-char-sequence:
 q-char
 q-char-sequence q-char

q-char:
 any member of the source character set except the new-line character and "

Preprocessing numbers

pp-number:
 digit
 . digit
 pp-number digit
 pp-number identifier-nondigit
 pp-number e sign
 pp-number E sign
 pp-number p sign
 pp-number P sign
 pp-number .

¹ binary-constant, binary-prefix, and binary-digit are Microsoft-specific extensions.

See also

C Language Syntax Summary