Calculating Execution Time with time() Function in C++

c++ctimetime

I was given the following HomeWork assignment,

Write a program to test on your computer how long it takes to do
nlogn, n2, n5, 2n, and n! additions for n=5, 10, 15, 20.

I have written a piece of code but all the time I am getting the time of execution 0. Can anyone help me out with it? Thanks

#include <iostream>
#include <cmath>
#include <ctime>
using namespace std;
int main()
{
 float n=20;
 time_t start, end, diff;
  start = time (NULL);
  cout<<(n*log(n))*(n*n)*(pow(n,5))*(pow(2,n))<<endl;
  end= time(NULL);
 diff = difftime (end,start);
 cout <<diff<<endl;
 return 0;
}

Best Answer

better than time() with second-precision is to use a milliseconds precision. a portable way is e.g.

int main(){
clock_t start, end;
double msecs;

start = clock();
/* any stuff here ... */
end = clock();
msecs = ((double) (end - start)) * 1000 / CLOCKS_PER_SEC;
return 0;
}

Related Solutions

C++ Execution Time – How to Calculate?

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;
}

C++ Time Calculation – Efficient Methods and Examples

Here is what I use to print time in milliseconds.

void StartTimer( _int64 *pt1 )
{
   QueryPerformanceCounter( (LARGE_INTEGER*)pt1 );
}

double StopTimer( _int64 t1 )
{
   _int64 t2, ldFreq;

   QueryPerformanceCounter( (LARGE_INTEGER*)&t2 );
   QueryPerformanceFrequency( (LARGE_INTEGER*)&ldFreq );
   return ((double)( t2 - t1 ) / (double)ldFreq) * 1000.0;
}

Use it like this:

    _int64 t1;

    StartTimer( &t1 );

    // do some stuff

    printf( "Time = %.3f\n", StopTimer( t1 ));

Best Answer

Related Solutions

C++ Execution Time – How to Calculate?

C++ Time Calculation – Efficient Methods and Examples

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