difftime(S)                    6 January 1993                    difftime(S)


 Name

    difftime - computes the difference between time values

 Syntax


    cc  . . .  -lc


    #include <time.h>

    double difftime(time2, time1)
    time_t time2;
    time_t time1;


 Description

    The difftime function computes the difference of time2 - time1.

    See the example which follows.

 Return value

    The difftime function returns the elapsed time in seconds from time1 to
    time2 as a double-precision number.

 See also

    ctime(S), mktime(S), nlcxtime(S), stime(S), time(S)

 Standards conformance

    difftime is conformant with:
    ANSI X3.159-1989 Programming Language -- C.

 Example


       #include <time.h>

       int mark[10000];

       main()
       {
               time_t  start, finish;
               register int i, loop, n, num, step;
               printf("This program takes about 3 minutes ");
               printf("on an AT and 8 on a PC.\n Working...\n");
               time(&start);

               for (loop = 0; loop < 1000; ++loop)
                  for (num = 0,n = 3; n < 10000; n += 2)
                       if (!mark[n])
                          {
                          /* printf("%d\n",n); */
                          step = 2*n;
                          for (i = 3*n; i < 10000; i += step)
                            mark[i] = -1;
                          ++num;
                          }
               time(&finish);

               /* Prints average of 1000 loops through "sieve": */
               printf("\nProgram takes %f seconds to find %d primes.\n",
               difftime(finish, start), num);
       }


    Output:

       Program takes 0.482000 seconds to find 1228 primes.

    This program calculates the amount of time needed to find the prime num-
    bers between 3 and 10,000. To display the prime numbers, delete the
    outermost loop and the comment delimiters around the expression
    printf("%d",n);.