time_get is used to parse a character sequence,
extracting components of a time or date into a tm object.
Each get member parses a format as produced by a corresponding format specifier to
time_put<>::put.
If the sequence being parsed matches the correct format, the corresponding
members of the
tm
argument are set to the values used to produce the sequence; otherwise
either an error is reported or unspecified values are assigned.254
In
other words, user confirmation is required for reliable parsing of
user-entered dates and times, but machine-generated formats can be
parsed reliably.
This allows parsers to be aggressive about
interpreting user variations on standard formats.