How can I measure CPU time and wall clock time on both Linux/Windows?

Here's a copy-paste solution that works on both Windows and Linux as well as C and C++.

As mentioned in the comments, there's a boost library that does this. But if you can't use boost, this should work:

//  Windows#ifdef _WIN32#include <Windows.h>double get_wall_time(){    LARGE_INTEGER time,freq;    if (!QueryPerformanceFrequency(&freq)){        //  Handle error        return 0;    }    if (!QueryPerformanceCounter(&time)){        //  Handle error        return 0;    }    return (double)time.QuadPart / freq.QuadPart;}double get_cpu_time(){    FILETIME a,b,c,d;    if (GetProcessTimes(GetCurrentProcess(),&a,&b,&c,&d) != 0){        //  Returns total user time.        //  Can be tweaked to include kernel times as well.        return            (double)(d.dwLowDateTime |            ((unsigned long long)d.dwHighDateTime << 32)) * 0.0000001;    }else{        //  Handle error        return 0;    }}//  Posix/Linux#else#include <time.h>#include <sys/time.h>double get_wall_time(){    struct timeval time;    if (gettimeofday(&time,NULL)){        //  Handle error        return 0;    }    return (double)time.tv_sec + (double)time.tv_usec * .000001;}double get_cpu_time(){    return (double)clock() / CLOCKS_PER_SEC;}#endif

There's a bunch of ways to implement these clocks. But here's what the above snippet uses:

For Windows:

• Wall Time: Performance Counters
• CPU Time: GetProcessTimes()

For Linux:

• Wall Time: gettimeofday()
• CPU Time: clock()

And here's a small demonstration:

#include <math.h>#include <iostream>using namespace std;int main(){    //  Start Timers    double wall0 = get_wall_time();    double cpu0  = get_cpu_time();    //  Perform some computation.    double sum = 0;#pragma omp parallel for reduction(+ : sum)    for (long long i = 1; i < 10000000000; i++){        sum += log((double)i);    }    //  Stop timers    double wall1 = get_wall_time();    double cpu1  = get_cpu_time();    cout << "Wall Time = " << wall1 - wall0 << endl;    cout << "CPU Time  = " << cpu1  - cpu0  << endl;    //  Prevent Code Elimination    cout << endl;    cout << "Sum = " << sum << endl;}

Output (12 threads):

Wall Time = 15.7586CPU Time  = 178.719Sum = 2.20259e+011

C++11. Much easier to write!

Use std::chrono::system_clock for wall clock and std::clock for cpu clockhttp://en.cppreference.com/w/cpp/chrono/system_clock

#include <cstdio>#include <ctime>#include <chrono>.... std::clock_t startcputime = std::clock();do_some_fancy_stuff();double cpu_duration = (std::clock() - startcputime) / (double)CLOCKS_PER_SEC;std::cout << "Finished in " << cpu_duration << " seconds [CPU Clock] " << std::endl;auto wcts = std::chrono::system_clock::now();do_some_fancy_stuff();std::chrono::duration<double> wctduration = (std::chrono::system_clock::now() - wcts);std::cout << "Finished in " << wctduration.count() << " seconds [Wall Clock]" << std::endl;

Et voilà, easy and portable! No need for #ifdef _WIN32 or LINUX!

You could even use chrono::high_resolution_clock if you need more precisionhttp://en.cppreference.com/w/cpp/chrono/high_resolution_clock

To give a concrete example of @lip's suggestion to use boost::timer if you can (tested with Boost 1.51):

#include <boost/timer/timer.hpp>// this is wallclock AND cpu timeboost::timer::cpu_timer timer;... run some computation ...boost::timer::cpu_times elapsed = timer.elapsed();std::cout << " CPU TIME: " << (elapsed.user + elapsed.system) / 1e9 << " seconds"          << " WALLCLOCK TIME: " << elapsed.wall / 1e9 << " seconds"          << std::endl;