Get a timestamp in C in microseconds?

How do I get a microseconds timestamp in C?

I'm trying to do:

struct timeval tv;
gettimeofday(&tv,NULL);
return tv.tv_usec;

But this returns some nonsense value that if I get two timestamps, the second one can be smaller or bigger than the first (second one should always be bigger). Would it be possible to convert the magic integer returned by gettimeofday to a normal number which can actually be worked with?

You need to add in the seconds, too:

unsigned long time_in_micros = 1000000 * tv.tv_sec + tv.tv_usec;

Note that this will only last for about 2³²/10⁶ =~ 4295 seconds, or roughly 71 minutes though (on a typical 32-bit system).

You have two choices for getting a microsecond timestamp. The first (and best) choice, is to use the timeval type directly:

struct timeval GetTimeStamp() {
    struct timeval tv;
    gettimeofday(&tv,NULL);
    return tv;
}

The second, and for me less desirable, choice is to build a uint64_t out of a timeval:

uint64_t GetTimeStamp() {
    struct timeval tv;
    gettimeofday(&tv,NULL);
    return tv.tv_sec*(uint64_t)1000000+tv.tv_usec;
}

struct timeval contains two components, the second and the microsecond. A timestamp with microsecond precision is represented as seconds since the epoch stored in the tv_sec field and the fractional microseconds in tv_usec. Thus you cannot just ignore tv_sec and expect sensible results.

If you use Linux or *BSD, you can use timersub() to subtract two struct timeval values, which might be what you want.