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Section: 29.13 [time.parse] Status: NAD Submitter: Howard Hinnant Opened: 2019-09-02 Last modified: 2020-09-06
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from_stream overloads may need to set various formatting state and flags of the basic_istream to implement the parsing functionality. Such settings must not persist beyond the parsing functions. Thus these functions need to save and restore any settings on the basic_istream they may need to change.
[2019-10 Priority set to 3 after reflector discussion]
[2020-02, Prague; Close as NAD]LWG reviewed the issue and decided no change is needed. Unless specified to change the flags, it's assumed that the stream flags are unchanged by any input function.
This wording is relative to N4830.
[Drafting note: The modification of 29.13 [time.parse] p1 is intended to be non-conflictingly mergeable with the change suggested by LWG 3269 at the same paragraph.]
Modify 29.13 [time.parse] as indicated:
-1- Each parse overload specified in this subclause calls from_stream unqualified, so as to enable argument dependent lookup (6.5.4 [basic.lookup.argdep]).[…] -10- All from_stream overloads behave as unformatted input functions, except that they have an unspecified effect on the value returned by subsequent calls to basic_istream<>::gcount(). Each overload takes a format string containing ordinary characters and flags which have special meaning. Each flag begins with a %. Some flags can be modified by E or O. During parsing each flag interprets characters as parts of date and time types according to Table [tab:time.parse.spec]. Some flags can be modified by a width parameter given as a positive decimal integer called out as N below which governs how many characters are parsed from the stream in interpreting the flag. All characters in the format string that are not represented in Table [tab:time.parse.spec], except for white space, are parsed unchanged from the stream. A white space character matches zero or more white space characters in the input stream.