The meaning of real, user, and sys in output of Linux time command
linux, time
Solution
If you take a look at the manpage (`man time`), it states:
The time command runs the specified program command with the given arguments. When command finishes, time writes a message to standard output giving timing statistics about this program run. These statistics consist of (i) the elapsed real time between invocation and termination, (ii) the user CPU time (the sum of the tms_utime and tms_cutime values in a struct tms as returned by times(2)), and (iii) the system CPU time (the sum of the tms_stime and tms_cstime values in a struct tms as returned by times(2)).
Basically though, the `user` time is how long your program was running on the CPU, and the `sys` time was how long your program was waiting for the operating system to perform tasks for it. If you're interested in benchmarking, `user + sys` is a good metric to use. `real` can be affected by other running processes, and is less consistent.
Problem
``` $ time ./Test real 0m2.906s user 0m2.887s sys 0m0.017s ``` Here is the program code: ``` #include <iostream> #include <map> void func_a() { std::map<int, int> m; for (unsigned int i = 0; i < 10000; i++) { m.insert(std::pair<int, int>(i, i)); } } void func_b() { std::map<int, int> m; for (unsigned int i = 0; i < 1000000; i++) { m.insert(std::pair<int, int>(i, i)); } } int main() { func_a(); func_b(); return 0; } ```