I'm currently using a explicit cast to unsigned long long and using %llu to print it, but since size_t has the %z specifier, why clock_t doesn't have one? There isn't even a macro for it. Maybe I can assume that on a x64 system (OS and CPU) size_t has 8 byte in length (and even in this case, they have provided %z), but what about clock_t?
+1
A:
It's probably because clock ticks is not a very well-defined unit. You can convert it to seconds and print it as a double:
time_in_seconds = (double)time_in_clock_ticks / (double)CLOCKS_PER_SEC;
printf("%g seconds", seconds);
The CLOCKS_PER_SEC macro expands to an expression representing the number of clock ticks in a second.
lemonad
2009-07-04 23:12:30
+1
A:
As far as I know, the way you're doing is the best. Except that clock_t may be a real type:
time_tandclock_tshall be integer or real-floating types.
http://www.opengroup.org/onlinepubs/009695399/basedefs/sys/types.h.html
Bastien Léonard
2009-07-04 23:14:23
Very well stated, I've forgotten about it possibly being a floating point type.
Spidey
2009-07-05 03:29:18
+1
A:
The C standard has to accomodate a wide variety of architectures, which makes it impossible to make any further guarantees aside from the fact that the internal clock type is arithmetic.
In most cases, you're interested in time intervals, so I'd convert the difference in clock ticks to milliseconds. An unsigned long is large enough to represent an interval of nearly 50 days even if its 32bit, so it should be large enough for most cases:
clock_t start;
clock_t end;
unsigned long millis = (end - start) * 1000 / CLOCKS_PER_SEC;
Christoph
2009-07-05 00:19:13
That's exactly why I can't imagine a macro for clock_t printing format isn't specified in any headers.
Spidey
2009-07-05 03:30:29
@Spidey: but what should the output format be if you can't make any guesses on the representation? Remember, it's not specified if `clock_t` will be an integer or floating point value; if you want to do anything useful, you *have* to relate it to `CLOCKS_PER_SEC`, and that's beyond the domain of `printf()`
Christoph
2009-07-05 03:39:55
@Christoph: since clock_t is not defined, CLOCKS_PER_SEC, afaik, is not either, and it is of the same type as clock_t. Since clock_t doesn't usually make it to production, I don't care what type it is and I won't rely on it to make any parsing.But I see the difference in that size_t is some integer type, and clock_t is not (not always), so we're trapped with explicit casting.
Spidey
2009-07-06 18:08:31
A:
//One of the way is by using gettimeofday function, one can find difference using this function.
unsigned long diff(struct timeval second, struct timeval first)
{
struct timeval lapsed;
struct timezone tzp;
unsigned long t;
if (first.tv_usec > second.tv_usec) {
second.tv_usec += 1000000;
second.tv_sec--;
}
lapsed.tv_usec = second.tv_usec - first.tv_usec;
lapsed.tv_sec = second.tv_sec - first.tv_sec;
t = lapsed.tv_sec*1000000 + lapsed.tv_usec;
printf("%lu,%lu - %lu,%lu = %ld,%ld\n",second.tv_sec,second.tv_usec,first.tv_sec,first.tv_usec,lapsed.tv_sec,lapsed.tv_usec);
return t;
}
rani
2009-12-22 11:23:01