size_t fmt_ulonglong(char *dest,unsigned long long source);
DESCRIPTIONfmt_ulonglong writes an ASCII representation ('0' to '9', base 10) of source to dest and returns the number of bytes written.
fmt_ulonglong does not append \0.
If dest equals FMT_LEN (i.e. is zero), fmt_ulonglong returns the number of bytes it would have written.
For convenience, fmt.h defines the integer FMT_ULONG to be big enough to contain every possible fmt_ulonglong output plus \0.