This one is just for fun, though I suppose I might not be the only one on the planet that ever needed to do this…

At my day job, I have a board that had a realtime clock, but no battery backup to retain the time. During startup, the system sends the current PC date and time (actually, it sends it in GMT, I believe, so looking at logs captured in different parts of the world will be easier — GMT is GMT anywhere on the planet ;-)

On startup, the board wants to log some things, but does not yet know the time. It had been using a hard-coded default time (like 1/1/2000). I wondered if the C compiler build date and time could be used to at least set the time based on when the firmware-in-use was compiled.

A quick chat with Bing’s AI (ChatGPT) and some experiments to make what it gave me far less bulky provided me with this:

int main()
{
    // Initialize time to when this firmware was built.
    const char *c_months = "JanFebMarAprMayJunJulAugSepOctNovDec";
    char monthStr[4];
    int year = 0;
    int month = 0;
    int day = 0;
    int hour = 0;
    int minute = 0;
    int second = 0;

    // “Mmm dd yyyy”
    strncpy(monthStr, __DATE__, 3);
    monthStr[3] = '\0';
    month = (strstr(c_months, monthStr) - c_months) / 3 + 1;

    day = atoi (&__DATE__[4]);
    year = atoi (&__DATE__[7]);

    printf ("%04d-%02d-%02d\n", year, month, day);

    // “hh:mm:ss”
    hour = atoi (&__TIME__[0]);
    minute = atoi (&__TIME__[3]);
    second = atoi (&__TIME__[6]);

    printf ("%02d:%02d:%02d\n", hour, minute, second);

    return 0;
}

This works by taking the compiler-generated macros of “__DATE__” and “__TIME__” and parsing out the values we want so they can be passed to a realtime clock routine or whatever.

In my case, this is not the code I am using since our embedded compiler handled __DATE__ in a different format. (It uses “dd-Mmm-yy” for some reason, while the standard C formatting appears to be “Mmm dd yyyy”.) But, the concept is similar.

Of course, as soon as I tested this, I found another issue. My board would power up and set to the build date (which is central standard time) and then when the system is connected, a new date/time is sent in GMT, which is currently 5 (or is it 6?) hours different, setting the clock back in time.

This makes log entries a bit odd ;-) but that’s a problem for another day.

Until then…