How to compute run time for a C program in ubuntu

Question

I tried >>time ./a.out

got

real 0m0.035s

user 0m0.008s

sys  0m0.004s

what it really means?

when I repeated I got

real 0m0.012s

user 0m0.000s

sys  0m0.012s

if I try this many times each time I am getting different output why? how can I solve it.

Answer 1

Each of those are the different runtimes of your program.

• Real is the actual wallclock time it took to run

• sys is the amount of time the system spent while executing your program (i.e. time spent by the kernel)

• user is the amount of time that was spent in user-mode executing it (i.e. time spent excuting where you weren't in the kernel).

Answer 2

There is no "solution" because there is no problem. You are running a multi tasking system and it depends on the load how fast you get the response. What you can do is running it a few times and take the average as "guide".