© 2005 John Abbott
GNU Free Documentation License, Version 1.2

CoCoALib Documentation Index

User documentation for CpuTime and RealTime

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();
    cout << "Time taken (in seconds) is " << CpuTime()-t0 << endl;
    return 0;

In contrast 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;

Maintainer documentation for CpuTime

It works on GNU/Linux and MacOSX. I hope someone else will deal with the portability issues.

Bugs, Shortcomings, and other ideas

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.