How can I improve/replace sprintf, which I've measured to be a performance hotspot?

Question

Through profiling I've discovered that the sprintf here takes a long time. Is there a better performing alternative that still handles the leading zeros in the y/m/d h/m/s fields?

SYSTEMTIME sysTime;
GetLocalTime( &sysTime );
char buf[80];
for (int i = 0; i < 100000; i++)
{

    sprintf(buf, "%4d-%02d-%02d %02d:%02d:%02d",
        sysTime.wYear, sysTime.wMonth, sysTime.wDay, 
        sysTime.wHour, sysTime.wMinute, sysTime.wSecond);

}

---

Note: The OP explains in the comments that this is a stripped-down example. The "real" loop contains additional code that uses varying time values from a database. Profiling has pinpointed sprintf() as the offender.

Answer 1

If you were writing your own function to do the job, a lookup table of the string values of 0 .. 61 would avoid having to do any arithmetic for everything apart from the year.

edit: Note that to cope with leap seconds (and to match strftime()) you should be able to print seconds values of 60 and 61.

char LeadingZeroIntegerValues[62][] = { "00", "01", "02", ... "59", "60", "61" };

Alternatively, how about strftime()? I've no idea how the performance compares (it could well just be calling sprintf()), but it's worth looking at (and it could be doing the above lookup itself).