5 Lexical conventions [lex]

5.13 Literals [lex.literal]

5.13.4 Floating-point literals [lex.fcon]

floating-point-literal:
decimal-floating-point-literal
hexadecimal-floating-point-literal
decimal-floating-point-literal:
fractional-constant exponent-part floating-point-suffix
digit-sequence exponent-part floating-point-suffix
hexadecimal-floating-point-literal:
hexadecimal-prefix hexadecimal-fractional-constant binary-exponent-part floating-point-suffix
hexadecimal-prefix hexadecimal-digit-sequence binary-exponent-part floating-point-suffix
fractional-constant:
digit-sequence . digit-sequence
digit-sequence .
hexadecimal-fractional-constant:
hexadecimal-digit-sequence . hexadecimal-digit-sequence
hexadecimal-digit-sequence .
exponent-part:
e sign digit-sequence
E sign digit-sequence
binary-exponent-part:
p sign digit-sequence
P sign digit-sequence
sign: one of
+ -
digit-sequence:
digit
digit-sequence ' digit
floating-point-suffix: one of
f l F L
1
#
The type of a floating-point-literal is determined by its floating-point-suffix as specified in Table 10.
Table 10: Types of floating-point-literals   [tab:lex.fcon.type]
floating-point-suffix
type
none
double
f or F
float
l or L
long double
2
#
In the significand, the sequence of digits or hexadecimal-digits and optional period are interpreted as a base N real number s, where N is 10 for a decimal-floating-point-literal and 16 for a hexadecimal-floating-point-literal.
[Note
:
Any optional separating single quotes are ignored when determining the value.
— end note
]
If an exponent-part or binary-exponent-part is present, the exponent e of the floating-point-literal is the result of interpreting the sequence of an optional sign and the digits as a base 10 integer.
Otherwise, the exponent e is 0.
The scaled value of the literal is for a decimal-floating-point-literal and for a hexadecimal-floating-point-literal.
[Example
:
The floating-point-literals 49.625 and 0xC.68p+2 have the same value.
The floating-point-literals 1.602'176'565e-19 and 1.602176565e-19 have the same value.
— end example
]
3
#
If the scaled value is not in the range of representable values for its type, the program is ill-formed.
Otherwise, the value of a floating-point-literal is the scaled value if representable, else the larger or smaller representable value nearest the scaled value, chosen in an implementation-defined manner.