Effects: Attempts to parse the input stream 
is
into the 
utc_time tp using
the format flags given in the NTCTS 
fmt
as specified in 
[time.parse].  If the parse fails to decode a valid date,
is.setstate(ios_base::failbit) is called and
tp is not modified
.If 
%Z is used and successfully parsed,
that value will be assigned to 
*abbrev if 
abbrev is non-null
.If 
%z (or a modified variant) is used and successfully parsed,
that value will be assigned to 
*offset if 
offset is non-null
.Additionally, the parsed offset will be subtracted from
the successfully parsed timestamp
prior to assigning that difference to 
tp.