How do I get milliseconds since midnight UTC in C?

Question

The time function in time.h gives milliseconds since the epoch.

Answer 1

This is the precise way:

struct timeval tv;
int msec = -1;
if (gettimeofday(&tv, NULL) == 0)
{
    msec = ((tv.tv_sec % 86400) * 1000 + tv.tv_usec / 1000);
}

That will store into msec the number of milliseconds since midnight. (Or -1 if there was an error getting the time.)

Although it's usually a bad idea to store time-values in an int, I'm being a little cavalier and assuming int is at least 32-bit, and can easily accommodate the range (-1) to 86,400,000.

But I don't know if it's worth all the effort.