calculating execution time in c++

user_105167 0
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I have written a c++ program , I want to know how to calculate the time taken for execution so I won't exceed the time limit.

#include<iostream>

using namespace std;

int main ()
{
    int st[10000],d[10000],p[10000],n,k,km,r,t,ym[10000];
    k=0;
    km=0;
    r=0;
    scanf("%d",&t);
    for(int y=0;y<t;y++)
    {
    scanf("%d",&n);
    for(int i=0;i<n;i++)
    {
            cin>>st[i] >>d[i] >>p[i];
    }
    for(int i=0;i<n;i++)
    {
            for(int j=i+1;j<n;j++)
            {
                    if((d[i]+st[i])<=st[j])
                    {
                              k=p[i]+p[j];
                    }
                    if(k>km)
                    km=k;
            }
        if(km>r)
        r=km;
    }
    ym[y]=r;
}
    for( int i=0;i<t;i++)
    {
         cout<<ym[i]<<endl;
    }


    //system("pause");
    return 0;
}

this is my program and i want it to be within time limit 3 sec !! how to do it ? yeah sorry i meant execution time !!

execution-time c++
9 Answers

If you have cygwin installed, from it's bash shell, run your executable, say MyProgram, using the time utility, like so:

/usr/bin/time ./MyProgram

This will report how long the execution of your program took -- the output would look something like the following:

real    0m0.792s
user    0m0.046s
sys     0m0.218s

You could also manually modify your C program to instrument it using the clock() library function, like so:

#include <time.h>
int main(void) {
    clock_t tStart = clock();
    /* Do your stuff here */
    printf("Time taken: %.2fs\n", (double)(clock() - tStart)/CLOCKS_PER_SEC);
    return 0;
}
user_736530

Note: the question was originally about compilation time, but later it turned out that the OP really meant execution time. But maybe this answer will still be useful for someone.

For Visual Studio: go to Tools / Options / Projects and Solutions / VC++ Project Settings and set Build Timing option to 'yes'. After that the time of every build will be displayed in the Output window.

Alex_Jenter_220460

This looks like Dijstra's algorithm. In any case, the time taken to run will depend on N. If it takes more than 3 seconds there isn't any way I can see of speeding it up, as all the calculations that it is doing need to be done.

Depending on what problem you're trying to solve, there might be a faster algorithm.

user_1087190

You can try below code for c++:

#include <chrono>


auto start = std::chrono::system_clock::now();
// Your Code to Execute //
auto end = std::chrono::system_clock::now();
std::cout << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count() << "ms" << std::endl;
user_26251760

If you are using C++ then you should try this below code as you would always get 0 as answer if you directly use @Ashutosh Mehra's answer.

#include <iostream>
#include <time.h>

using namespace std;

int main() {
    int a = 20000, sum=0;
    
    clock_t start = clock();
    for (int i=0; i<a; i++) {
        for (int k = 0; k<a; k++)
            sum += 1;
    }
    cout.precision(10);
    cout << fixed <<  float(clock() - start)/CLOCKS_PER_SEC  << endl;
    return 0;
}

Because in C++ you the float and double values will directly be rounded off. So I used the cout.precision(10) to set the output precision of any value to 10 digits after decimal.

user_123303380

shorter version of Ashutosh Mehra's answer:

/* including stuff here */
#include <time.h>
int main(void) {
    clock_t tStart = clock();
    /* stuff here */
    cout<<"Time taken: "<<(double)(clock() - tStart)/CLOCKS_PER_SEC;
    return 0;
}
user_191729510
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