Why is the child's lead time negative?

Question

I did a little test to find out how much time a child process is taking with fork () compared to the parent. However, by running this program, I get execution for the child to somehow come up with as negative.

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

int main(void){
    clock_t begin = clock();

    printf("Before fork\n");


    pid_t pid_return = fork();


    char* x;

    if(pid_return != 0){
        x = "Parent";
    }
    else{
        x = "Child";
    }

    clock_t end = clock();

    double time_spent = (double)(end - begin);
    printf("%s time spent: %f\n", x, time_spent);
}

Conclusion:

Before fork
Parent time spent: 197.000000
Child time spent: -2143.000000

Answer 1

clock()is not (wall clock), this is the amount of CPU used by the current process. Using fork(), you are supposedly reset this time to 0 in the child process (since it hasn't used any CPU yet). This is why it is endmuch smaller in the child element and subtracting the parent beginfrom it makes it negative.

Answer 2

, : parent clock , , clock fork.

:

#include <stdio.h>
#include <unistd.h>
#include <time.h>
#include <sys/types.h>

int main(void){
    printf("Before fork\n");
    pid_t pid_return = fork();
    clock_t time = clock();
    char* x;
    if(pid_return != 0){
        x = "Parent";
    } else{
        x = "Child";
    }
    printf("%s time : %f\n", x, (double)time);
}

child, , fork.

Before fork
Parent time : 2684.000000
Child time : 617.000000