How to calculate the execution time in C?

Question

How can I calculate the execution time in the following code:

#include   /* Core input/output operations                         */
#include 

        

Answer 1

Try this:

printf("    Time   : %lu\n", clock() );
printf("    Start Time   : %lds %ldus\n", tv1.tv_sec, tv1.tv_usec);
printf("    End Time   : %lds %ldus\n", tv2.tv_sec, tv2.tv_usec);

And for:

double timeval_subtract (result, x, y)

use the following to return the time difference in micro seconds:

long timeval_subtract (struct timeval * result, struct timeval * x, struct timeval * y)
{
   long usec = x->tv_sec * 1000000L + x->tv_usec;
   usec -= (y->tv_sec * 1000000L + y->tv_usec);

   result->tv_sec = usec / 1000000L;
   result->tv_usec = usec % 1000000L;

   return usec;
}

Depending on the difference of the two dates x and y the return value of the function timeval_subtract (not the value represented by result!) might be wrong, due to an overflow.

Assuming a long is 32bit wide this overflow will occur with differences larger than 4294s, for a long having 64bit (which should be the case an 64bit machines) the overflow whould occur after much later ... ;-)