Question

I want to find the time taken by another program to run ;
I am using following code;

system("time ./a.out > garb");

it is giving very weird output.

#include <stdio.h>

int main()
{

        long int i;

        for ( i = 0; i < 10000000; i++ ) {
                printf("Hello World!\n");
        }
        printf("C Program\n");
        return 0;
}

output

0.31user 0.10system 0:00.41elapsed 99%CPU (0avgtext+0avgdata 1744maxresident)k
0inputs+253912outputs (0major+149minor)pagefaults 0swaps

Answer 1

One way is to use wait3 or wait4 functions (if those are available in your system).

pid_t wait3(int *status, int options, struct rusage *rusage);    
pid_t wait4(pid_t pid, int *status, int options, struct rusage *rusage);

Your program will get resource usage of a child process after the child is exited.

All fields of struct rusage are not updated, but the first two fields tells what you want:

struct rusage {
    struct timeval ru_utime; /* user CPU time used */
    struct timeval ru_stime; /* system CPU time used */
    ...

Sum of ru_utime and ru_stime is the total CPU time used by the child process.

Using of wait3 / wait4 is not so simple as calling of system() function.

EDIT:
You should get same result by summing those two values of printout of time:

0.31user 0.10system