20 General utilities library [utilities]

20.20 Formatting [format]

20.20.2 Format string [format.string]

20.20.2.2 Standard format specifiers [format.string.std]

Table 67: Meaning of type options for floating-point types [tab:format.type.float]
Type
Meaning
a
If precision is specified, equivalent to to_chars(first, last, value, chars_format::hex, precision) where precision is the specified formatting precision; equivalent to to_chars(first, last, value, chars_format::hex) otherwise.
A
The same as a, except that it uses uppercase letters for digits above 9 and P to indicate the exponent.
e
Equivalent to to_chars(first, last, value, chars_format::scientific, precision) where precision is the specified formatting precision, or 6 if precision is not specified.
E
The same as e, except that it uses E to indicate exponent.
f, F
Equivalent to to_chars(first, last, value, chars_format::fixed, precision) where precision is the specified formatting precision, or 6 if precision is not specified.
g
Equivalent to to_chars(first, last, value, chars_format::general, precision) where precision is the specified formatting precision, or 6 if precision is not specified.
G
The same as g, except that it uses E to indicate exponent.
none
If precision is specified, equivalent to to_chars(first, last, value, chars_format::general, precision) where precision is the specified formatting precision; equivalent to to_chars(first, last, value) otherwise.