Millisecond timing C++ - c++

Question

I want to time the real-time performance of some C++ functions I have written. How do I get the timing in milliseconds scale?
I know how to get time in seconds via
start=clock()
diff=(clock()-start)/(double) CLOCKS_PER_SEC
cout<<diff
I am using Ubuntu-Linux OS and g++ compiler.

Answer 1

In Linux, take a look at clock_gettime(). It can essentially give you the time elapsed since an arbitrary point, in nanoseconds (which should be good enough for you).
Note that it is specified by the POSIX standard, so you should be fine using it on Unix-derived systems.

Answer 2

Try diff = (clock() - start) * 1000.0 / CLOCKS_PER_SEC;
The idea is that you multiply the number of clocks by 1000, so that whereas before you might get 2 (seconds), you now get 2000 (milliseconds).

Answer 3

Notes:
On my Dell desktop, which is reasonably quick ...
ubuntu bogomips peak at 5210
time(0) takes about 80 nano-seconds (30 million calls in 2.4 seconds)
time(0) allows me to measure
clock_gettime() which takes about 1.3 u-seconds per call (2.2 million in 3 seconds)
(I don't remember how many nano-seconds per time step)
So typically, I use the following, with about 3 seconds of invocations.
// ////////////////////////////////////////////////////////////////////////////
void measuring_something_duration()
...
uint64_t start_us = dtb::get_system_microsecond();
do_something_for_about_3_seconds()
uint64_t test_duration_us = dtb::get_system_microsecond() - start_us;
uint64_t test_duration_ms = test_duration_us / 1000;
...
which use these functions
// /////////////////////////////////////////////////////////////////////////////
uint64_t mynamespace::get_system_microsecond(void)
{
uint64_t total_ns = dtb::get_system_nanosecond(); // see below
uint64_t ret_val = total_ns / NSPUS; // NanoSecondsPerMicroSeconds
return(ret_val);
}
// /////////////////////////////////////////////////////////////////////////////
uint64_t mynamespace::get_system_nanosecond(void)
{
//struct timespec { __time_t tv_sec; long int tv_nsec; }; -- total 8 bytes
struct timespec ts;
// CLOCK_REALTIME - system wide real time clock
int status = clock_gettime(CLOCK_REALTIME, &ts);
dtb_assert(0 == status);
// to 8 byte from 4 byte
uint64_t uli_nsec = ts.tv_nsec;
uint64_t uli_sec = ts.tv_sec;
uint64_t total_ns = uli_nsec + (uli_sec * NSPS); // nano-seconds-per-second
return(total_ns);
}
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