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C++ Literal Constants

Literal constants (often referred to as literals or constants) are invariants whose values are implied by their representations.

Form

literal-constant	::=	`integer-literal`
	\|	`float-literal`
	\|	`string-literal`
	\|	`boolean-literal`
integer-literal	::=	`unsigned-literal`
	\|	`unsigned-literal integer-suffix`
	\|	`char-literal`
unsigned-literal	::=	`decimal-literal`
	\|	`octal-literal`
	\|	`hex-literal`
decimal-literal	::=	`nonzero-digit digit ∗`
octal-literal	::=	`0 octal-digit ∗`
hex-literal	::=	`hex-prefix hex-digit hex-digit ∗`
hex-prefix	::=	`0X`
	\|	`0x`
integer-suffix	::=	`long-suffix`
	\|	`unsigned-suffix`
	\|	`unsigned-suffix long-suffix`
	\|	`long-suffix unsigned-suffix`
long-suffix	::=	`L`
	\|	`l`
unsigned-suffix	::=	`U`
	\|	`u`
float-literal	::=	`unsigned-float`
	\|	`unsigned-float float-suffix`
unsigned-float	::=	`simple-float`
	\|	`exponential-float`
simple-float	::=	`digit-sequence .`
	\|	`digit-sequence . digit-sequence`
	\|	`. digit-sequence`
exponential-float	::=	`digit-sequence exponent-part`
	\|	`simple-float exponent-part`
exponent-part	::=	`exponent-prefix exponent`
exponent-prefix	::=	`E`
	\|	`e`
exponent	::=	`sign digit-sequence`
	\|	`digit-sequence`
digit-sequence	::=	`digit digit ∗`
float-suffix	::=	`L`
	\|	`l`
	\|	`F`
	\|	`f`
char-literal	::=	`' c-character ∗ '`
	\|	`L' c-character ∗ '`
s-character	::=	`ASCII codes 1 to 126 except for ', \, carriage return, and line feed`
	\|	`escape-sequence`
string-literal	::=	`" s-character ∗ "`
	\|	`L" s-character ∗ "`
s-character	::=	`ASCII codes 1 to 126 except for ", \, carriage return, and line feed`
	\|	`escape-sequence`
escape-sequence	::=	`simple-escape`
	\|	`octal-escape`
	\|	`hex-escape`
simple-escape	::=	`\a \| \b \| \f \| \n \| \r \| \t \| \v \| \' \| \" \| \? \| \\`
octal-escape	::=	`\ octal-digit`
	\|	`\ octal-digit octal-digit`
	\|	`\ octal-digit octal-digit octal-digit`
hex-escape	::=	`\x hex-digit ∗`
boolean-literal	::=	`true`
	\|	`false`
null-literal	::=	`null`
octal-digit	::=	`0 \| 1 \| 2 \| 3 \| 4 \| 5 \| 6 \| 7`
digit	::=	`0 \| 1 \| 2 \| 3 \| 4 \| 5 \| 6 \| 7 \| 8 \| 9`
nonzero-digit	::=	`1 \| 2 \| 3 \| 4 \| 5 \| 6 \| 7 \| 8 \| 9`
hex-digit	::=	`0 \| 1 \| 2 \| 3 \| 4 \| 5 \| 6 \| 7 \| 8 \| 9`
		`\| A \| B \| C \| D \| E \| F \| a \| b \| c \| d \| e \| f`
sign	::=	`+ \| -`

**C++ Literals**
Type	Base	Example	Description
char *	ASCII	"hello"	Any string of characters enclosed in double quotes (") (see Note 1)
char	ASCII	'1'	One character in single quotes (')
unsigned short int	ASCII	L'ab'	One or two characters in single quotes ('), preceded by the letter L
int	octal	01	Any octal number (digits 0-7) beginning with a 0 (zero)
	decimal	1	Any decimal number (digits 0-9) not beginning with a 0 (zero)
	hexadecimal	0x1	0X (zero X) or 0x (zero x) followed by any hexadecimal number (digits 0-F)
	ASCII	'ABC'	Two to four characters in single quotes (')
unsigned int	octal	01U	Any octal number (digits 0-7) beginning with a 0 (zero) and followed by U or u
	decimal	1U	Any decimal number (digits 0-9) not beginning with a 0 (zero) and followed by U or u
	hexadecimal	0x1U	0X (zero X) or 0x (zero x) followed by any hexadecimal number (digits 0-F) and followed by U or u
long int	octal	01L	Any octal number (digits 0-7) beginning with a 0 (zero) and followed by L or l
	decimal	1L	Any decimal number (digits 0-9) not beginning with a 0 (zero) and followed by L or l
	hexadecimal	0x1L	0X (zero X) or 0x (zero x) followed by any hexadecimal number (digits 0-F) and followed by L or l
unsigned long int	octal	01UL	Any octal number (digits 0-7) beginning with a 0 (zero) and followed by U or u and L or l
	decimal	1UL	Any decimal number (digits 0-9) not beginning with a 0 (zero) and followed by U or u and L or l
	hexadecimal	0x1UL	0X (zero X) or 0x (zero x) followed by any hexadecimal number (digits 0-F) and followed by U or u and L or l
float	decimal	12.3F	Any number (digits 0-9) containing a decimal point (.) and followed by F or f
float	decimal	12E1F	Any number (digits 0-9) followed by E or e, followed by an exponent of 10 (12E1 = 12 * 101 = 120.), and followed by F or f
double	decimal	12.3	Any number (digits 0-9) containing a decimal point (.)
double	decimal	12E1	Any number (digits 0-9) followed by E or e and followed by an exponent of 10 (12E1 = 12 * 101 = 120.)
long double	decimal	12.3L	Any number (digits 0-9) containing a decimal point (.) and followed by L or l
long double	decimal	12E1L	Any number (digits 0-9) followed by E or e, followed by an exponent of 10 (12E1 = 12 * 101 = 120.), and followed by L or l
Notes: String constants are stored as the literal characters followed by a byte of binary 0. The value returned is a pointer to the first character.

**Escape Sequences**
Code	Character	Description
\\	\	Backslash
\'	'	Single Quote
\"	"	Double Quote
\?	?	Question Mark
\0	<NUL>	Binary 0
\a	<BEL>	Bell (Audible alert)
\b	<BS>	Back Space
\f	<FF>	Form Feed
\n	<NL>	New Line
\r	<CR>	Carriage Return
\t	<HT>	Horizontal Tab
\v	<VT>	Vertical Tab
Notes: These escape sequences are used within character or string literal constants. They each represent a single character.

**Numeric Escape Sequences**
Width	Code	Where
8 bit	\nnn	n = octal digit
8 bit	\xnn	n = hexadecimal digit
8 bit	\Xnn	n = hexadecimal digit
16 bit	\unnnn	n = hexadecimal digit
32 bit	\Unnnnnnnn	n = hexadecimal digit
Notes: These escape sequences are used within character or string literal constants. They each represent a 1, 2, or 4 bytes, as indicated by the width.

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