Effects: The first form steps through the sequence
from 
pattern to 
pat_end,
identifying characters that are part of a format sequence
.  Each character that is not part of a format sequence
is written to 
s immediately, and
each format sequence, as it is identified, results in a call to 
do_put;
thus, format elements and other characters are interleaved in the output
in the order in which they appear in the pattern
.Format sequences are identified by converting each character 
c to
a 
char value as if by 
ct.narrow(c, 0),
where 
ct is a reference to 
ctype<charT>
obtained from 
str.getloc().The first character of each sequence is equal to 
'%',
followed by an optional modifier character 
mod
and a format specifier character 
spec
as defined for the function 
strftime.If no modifier character is present, 
mod is zero
.For each valid format sequence identified,
calls 
do_put(s, str, fill, t, spec, mod).