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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-suffixopt
binary-constant1 integer-suffixopt
octal-constant integer-suffixopt
hexadecimal-constant integer-suffixopt

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-suffixopt
unsigned-suffix long-long-suffixopt
long-suffix unsigned-suffixopt
long-long-suffix unsigned-suffixopt

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-partopt floating-suffixopt
digit-sequence exponent-part floating-suffixopt

hexadecimal-floating-constant:
hexadecimal-prefix hexadecimal-fractional-constant binary-exponent-partopt floating-suffixopt
hexadecimal-prefix hexadecimal-digit-sequence binary-exponent-part floating-suffixopt

fractional-constant:
digit-sequenceopt . digit-sequence
digit-sequence .

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

sign: one of
+ -

digit-sequence:
digit
digit-sequence digit

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

binary-exponent-part:
p signopt digit-sequence
P signopt 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-sequenceopt "

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