iter_type put(iter_type s, ios_base& str, char_type fill, const tm* t,
const charT* pattern, const charT* pat_end) const;
iter_type put(iter_type s, ios_base& str, char_type fill, const tm* t,
char format, char modifier = 0) const;
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 mod245 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).
[ Note: The fill argument may be used in the implementation-defined formats or by derivations. A space character is a reasonable default for this argument. — end note ]
Although the C programming language defines no modifiers, most vendors do.