5 Lexical conventions [lex]

🔗 *floating-point-suffix*	type
🔗 none	double
🔗 f or F	float
🔗 l or L	long double
🔗 f16 or F16	std::float16_t
🔗 f32 or F32	std::float32_t
🔗 f64 or F64	std::float64_t
🔗 f128 or F128	std::float128_t
🔗 bf16 or BF16	std::bfloat16_t

The significand of a floating-point-literal is the fractional-constant or digit-sequence of a decimal-floating-point-literal or the hexadecimal-fractional-constant or hexadecimal-digit-sequence of a hexadecimal-floating-point-literal.

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 2:

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

s \times 10^{e}

for a decimal-floating-point-literal and

s \times 2^{e}

for a hexadecimal-floating-point-literal.

[Example 1:

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]

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.

[Example 2:

The following example assumes that std::float32_t is supported ([basic.extended.fp]).

std::float32_t x = 0.0f32; // value 0 is exactly representable std::float32_t y = 0.1f32; // rounded to one of two values nearest to 0.1 std::float32_t z = 1e1000000000f32; // either greatest finite value or positive infinity — end example]