How to use clock() in C++

问题

How do I call clock() in C++?

For example, I want to test how much time a linear search takes to find a given element in an array.

回答1:

#include <iostream>
#include <cstdio>
#include <ctime>

int main() {
    std::clock_t start;
    double duration;

    start = std::clock();

    /* Your algorithm here */

    duration = ( std::clock() - start ) / (double) CLOCKS_PER_SEC;

    std::cout<<"printf: "<< duration <<'\n';
}

回答2:

An alternative solution, which is portable and with higher precision, available since C++11, is to use std::chrono.

Here is an example:

#include <iostream>
#include <chrono>
typedef std::chrono::high_resolution_clock Clock;

int main()
{
    auto t1 = Clock::now();
    auto t2 = Clock::now();
    std::cout << "Delta t2-t1: " 
              << std::chrono::duration_cast<std::chrono::nanoseconds>(t2 - t1).count()
              << " nanoseconds" << std::endl;
}

Running this on ideone.com gave me:

Delta t2-t1: 282 nanoseconds

回答3:

clock() returns the number of clock ticks since your program started. There is a related constant, CLOCKS_PER_SEC, which tells you how many clock ticks occur in one second. Thus, you can test any operation like this:

clock_t startTime = clock();
doSomeOperation();
clock_t endTime = clock();
clock_t clockTicksTaken = endTime - startTime;
double timeInSeconds = clockTicksTaken / (double) CLOCKS_PER_SEC;

回答4:

On Windows at least, the only practically accurate measurement mechanism is QueryPerformanceCounter (QPC). std::chrono is implemented using it (since VS2015, if you use that), but it is not accurate to the same degree as using QueryPerformanceCounter directly. In particular it's claim to report at 1 nanosecond granularity is absolutely not correct. So, if you're measuring something that takes a very short amount of time (and your case might just be such a case), then you should use QPC, or the equivalent for your OS. I came up against this when measuring cache latencies, and I jotted down some notes that you might find useful, here; https://github.com/jarlostensen/notesandcomments/blob/master/stdchronovsqcp.md

回答5:

#include <iostream>
#include <ctime>
#include <cstdlib> //_sleep()  --- just a function that waits a certain amount of milliseconds

using namespace std;

int main()
{

    clock_t cl;     //initializing a clock type

    cl = clock();   //starting time of clock

    _sleep(5167);   //insert code here

    cl = clock() - cl;  //end point of clock

    _sleep(1000);   //testing to see if it actually stops at the end point

    cout << cl/(double)CLOCKS_PER_SEC << endl;  //prints the determined ticks per second (seconds passed)


    return 0;
}

//outputs "5.17"

回答6:

Probably you might be interested in timer like this : H : M : S . Msec.

the code in Linux OS:

#include <iostream>
#include <unistd.h>

using namespace std;
void newline(); 

int main() {

int msec = 0;
int sec = 0;
int min = 0;
int hr = 0;


//cout << "Press any key to start:";
//char start = _gtech();

for (;;)
{
        newline();
                if(msec == 1000)
                {
                        ++sec;
                        msec = 0;
                }
                if(sec == 60)
                {
                        ++min;
                        sec = 0; 
                }
                if(min == 60)
                {
                        ++hr;
                        min = 0;
                }
        cout << hr << " : " << min << " : " << sec << " . " << msec << endl;
        ++msec;
        usleep(100000); 

}

    return 0;
}

void newline()
{
        cout << "\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n";
}

来源：https://stackoverflow.com/questions/3220477/how-to-use-clock-in-c

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c++

benchmarking

clock