CpuTime() returns a double whose value is the user CPU usage in
seconds since the start of the program (i.e. the amount of time the
processor has dedicated to your computation -- this may be rather less than
the real elapsed time if the computer is also busy with other tasks). For
instance, to find out how long func() takes to execute you can do the
following:
int main()
{
double t0 = CpuTime();
func();
cout << "Time taken (in seconds) is " << CpuTime()-t0 << endl;
return 0;
}
ElapsedTime() returns a double being the number of seconds elapsed
since the program was started (more-or-less).
The function RealTime() returns a double whose value is the number
of seconds elapsed since some fixed point in the past (on Unix/Linux boxes
this is typically 1st January 1970, sometimes called "the epoch").
WARNING we cannot guarantee the accuracy of these functions; as a rule of thumb you should regard time differences as having an imprecision of around 2% plus up to 0.2 seconds of unknown variation. So using these functions to measure a time difference less than 1 second is likely to produce a value with quite a large relative error.
As a convenience there is also the function DateTime(long& date, long& time)
which stores in date and time the current date and time
represented as decimal integers having the formats yyyymmdd & hhmmss
respectively. Example:
long date, time_unused;
DateTime(date, time_unused);
int YearToday = date/10000;
int MonthToday = (date/100)%100;
int DayToday = date%100;
It works on GNU/Linux and MacOSX. I hope someone else will deal with the portability issues.
2020-12-18: added ElapsedTime (should be portable).
Might not work on Microsoft platforms -- maybe this is really a feature?
I ignore the return values of getrusage and gettimeofday; I'd be
amazed if they could signal errors, but perhaps the code ought to check?
BOOST has probably solved this; apparently Bruno has a solution too.