measure time complexity

This is a discussion on measure time complexity within the C++ Programming forums, part of the General Programming Boards category; Hello I'd like to measure time complexity that its needed for some algorithm/function to complete in my c++ application. I'd ...

  1. #1
    l2u
    l2u is offline
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    measure time complexity

    Hello

    I'd like to measure time complexity that its needed for some algorithm/function to complete in my c++ application. I'd like to have it in miliseconds, double format (example: 0.253ms)

    I've tried doing the following:

    Code:
    #include <boost/date_time/posix_time/posix_time_types.hpp>
    
    //..
    
    boost::posix_time::ptime start = boost::posix_time::microsec_clock::universal_time();
    function();
    
    boost::posix_time::time_duration time = boost::posix_time::microsec_clock::universal_time() - start;
    std::cout << "done in: " << (double)(time.total_microseconds()/1000.0) << " ms\n";
    But this will only output 0.

    What am I doing wrong?

    Is there any better way of doing this?

    Thanks for help!

  2. #2
    Kernel hacker
    Join Date
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    Farncombe, Surrey, England
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    Have you considered that the microsecond precision in Boost may not actually reflect the TRUE precision of the system's clock timing?

    Just becuse the time is specified in microseconds, doesn't meant that it's supplied with microsecond precision. Most OS's supply the current time in 1-10 ms chunks.

    Try running your function 100 times or something like that...

    Note also that you can do quite a lot of regular instructions in a microsecond - around 2000-4000 on a 2GHz processor - so unless your function is quite comples, it may well take less than a microsecond to complete.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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