Syntax

#include <time.h>
double difftime(time_t time2, time_t time1);

difftime computes the difference in seconds between time2 and time1.

The difftime function returns the elapsed time in seconds from time1 to time2 as a double precision number. Type time_t is defined in <time.h>.

This example shows a timing application using difftime. The example calculates how long, on average, it takes to find the prime numbers from 2 to 10000.

#include <time.h>
#include <stdio.h>

#define  RUNS          1000
#define  SIZE          10000

int mark[SIZE];

int main(void)
{
   time_t start,finish;
   int i,loop,n,num;

   time(&start);

   /*  This loop finds the prime numbers between 2 and SIZE                   */

   for (loop = 0; loop < RUNS; ++loop) {
      for (n = 0; n < SIZE; ++n)
         mark[n] = 0;

      /*  This loops marks all the composite numbers with -1                  */

      for (num = 0, n = 2; n < SIZE; ++n)
         if (!mark[n]) {
            for (i = 2*n; i < SIZE; i += n)
               mark[i] = -1;
            ++num;
         }
   }
   time(&finish);
   printf("Program takes an average of %f seconds to find %d primes.\n",
      difftime(finish, start)/RUNS, num);
   return 0;

   /****************************************************************************
      The output should be similar to :

      Program takes an average of 0.106000 seconds to find 1229 primes.
   ****************************************************************************/
}

• asctime
  
• ctime
  
• gmtime
  
• localtime
  
• mktime
  
• strftime
  
• time

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