questions on clock(),time() and difftime() in time.h?

Question

int fib(int n,int a,int b){
    if (n==2){
        return a+b;
    }
    return fib(n-1,b,a+b);

}

int main() {
    time_t begin,end;
    begin = clock();
    fib(10000,0,1);
    end = clock();
    printf("%f",difftime(end,begin));
}




int main() {
    time_t begin,end;
    time(&begin);
    fib(10000,0,1);
    time(&end);
    printf("%f",(double)(end-begin)/CLOCKS_PER_SEC);
}

1)First question Why does my first main give prints me a time 288.000000,I'm assuming this is 288 milliseconds but in the documentation it is supposed to give me the result in seconds.I am on Mac by the way.

2)Second Question Why does the second main. Why does this print me the output time being 0.000000. I understand that time() give me a time_t structure that i put inside begin and end time_t structs and then i find the difference in seconds,doesn't seem to work.

Could you explain what is your expected Output? Do you try to print seconds between different times ? — Michi, Nov 07 '15 at 12:44
I expect something like `0.000198` because something like `200.000000` means 200 seconds which is wrong,and `0.000000` is also wrong. — Charana, Nov 07 '15 at 12:46
Yes i am trying to get the difference in seconds between two difference times. — Charana, Nov 07 '15 at 12:49

score 0 · Answer 1 · answered Nov 07 '15 at 13:01

Yes i am trying to get the difference in seconds between two difference times.

You could try something like the following approach:

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


void timeCheck(int *clock,int *minutes){
    int hour ;
    int minute ;
    time_t end, start;
    double diff;
    size_t seconds;


    start = (time_t)((clock[0] * 60 + clock[1]) * 60) ;
    end = (time_t)((minutes[0] * 60 + minutes[1]) * 60) ;

    if( end < start ){
        end += 24 * 60 * 60 ;
    }

    diff = difftime(end, start);

    hour = (int) diff / 3600;
    minute = (int) diff % 3600 / 60;
    printf("The difference is %d:%d\n", hour, minute);
    seconds = (size_t)(hour * 3600) + (size_t)(minute * 60);
    printf("Seconds = %zu\n",seconds);
}

int main(void) {
    int hour[] = {22,20};
    int minutes[] = {5,40};

    printf("Start time %d:%d\n",hour[0],hour[1]);
    printf("End time %d:%d\n\n",minutes[0],minutes[1]);

    timeCheck(hour,minutes);
    return 0;
}

Output:

Start time 22:20
End time 5:40

The difference is 7:20
Seconds = 26400

score 0 · Answer 2 · answered Nov 07 '15 at 13:14

The return type from clock() is clock_t - not necessarily seconds. Apple : clock. Which measures the number of ticks the CPU has used (CLOCKS_PER_SEC). This value is not necessarily milliseconds or seconds.

time() returns the number of whole seconds since a particular point in time (1/1/1970).

So calling time twice in quick succession, results in the same number of whole seconds.

difftime expects time_t (return type from time()) as its parameters and creates an elapsed time (in seconds).

Thus it is not correct to call for clock_t values.

questions on clock(),time() and difftime() in time.h?

2 Answers2

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