### difftime -- Compute Time Difference

Format

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

Language Level: ANSI, POSIX, XPG4
difftime computes the difference in seconds between time2 and time1.

Return Value
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>.

Example
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);

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

          The program takes an average of 0.106000 seconds to
          find 1229 prime.
       ************************************************************/
    }

asctime -- Convert Time to Character String
ctime -- Convert Time to Character String
gmtime -- Convert Time
localtime -- Convert Time
mktime -- Convert Local Time
strftime -- Convert to Formatted Time
time -- Determine Current Time
<time.h>