Issue 3962: What is the "decimal precision of the input"?

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3962. What is the "decimal precision of the input"?

Section: 29.13 [time.parse] Status: New Submitter: Jonathan Wakely Opened: 2023-07-28 Last modified: 2024-01-29

Priority: 3

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Discussion:

The %j flag talks about "the type being parsed" and %S talks about "the input time" and "the input", but doesn't really define which types those are.

[2023-11-02; Reflector poll]

Set priority to 3 after reflector poll.

Proposed resolution:

This wording is relative to N4950.

Modify 29.13 [time.parse] as indicated:

-?- In Table 102 the type Parsable denotes the type of the second argument to from_stream.

%j If ~~the type being parsed~~ Parsable is a specialization of duration, a decimal number of days.

%S The seconds as a decimal number. The modified command %NS specifies the maximum number of characters to read. If N is not specified, the default is 2 if Parsable is a calendrical type (29.8 [time.cal]) ~~if the input time has a precision convertible to seconds~~. Otherwise the default width is determined by the decimal precision of ~~the input~~ Parsable, determined in the same manner as hh_mm_ss::fractional_width (29.9 [time.hms]). If the number of fractional decimal digits for the type is zero, then the default for N is 2. Otherwise, it is 3 + W, where W is the number of fractional decimal digits. If N is less than 3, the field is interpreted as a decimal integer, otherwise ~~and~~ the field is interpreted as a long double in a fixed format. If encountered, the locale determines the decimal point character. Leading zeroes are permitted but not required. The modified command %OS interprets the locale's alternative representation.

`%j`	If ~~the type being parsed~~ `Parsable` is a specialization of `duration`, a decimal number of days.

`%S`	The seconds as a decimal number. The modified command `%NS` specifies the maximum number of characters to read. If `N` is not specified, the default is 2 if `Parsable` is a calendrical type (29.8 [time.cal]) ~~if the input time has a precision convertible to seconds~~. Otherwise the default width is determined by the decimal precision of ~~the input~~ `Parsable`, determined in the same manner as `hh_mm_ss::fractional_width` (29.9 [time.hms]). If the number of fractional decimal digits for the type is zero, then the default for `N` is 2. Otherwise, it is 3 + W, where W is the number of fractional decimal digits. If `N` is less than 3, the field is interpreted as a decimal integer, otherwise ~~and~~ the field is interpreted as a `long double` in a fixed format. If encountered, the locale determines the decimal point character. Leading zeroes are permitted but not required. The modified command `%OS` interprets the locale's alternative representation.