Mac 上的计时 C++ 程序

Question

I want to time my threading program on my mac and knew that for Linux environments, you can time it by doing: "time ./a.out".

I tried this on my mac terminal and it seems to be working but gives a little different output. The one on Linux will give output in the format: (random times btw) real 0m0.792s user 0m0.046s sys 0m0.218s

while this one gives: ./a.out 0.84s user 1.49s system 29% cpu 7.866 total

What is the main difference between "real" and "user" and is there any other types of commands to time the execution of programs?

Answer 1

This is well explained in the man pages, in both Linux and macOS.

Linux

These statistics consist of (i) the elapsed real time between invocation and termination , (ii) the user CPU time and (iii) the system CPU time.

macOS

time writes the total time elapsed, the time consumed by system overhead, and the time used to execute utility to the standard error stream.

• Real means the total time needed to execute the whole program, including startup and exit.
• User is basically your own code.
• System is the time spent calling system functions.

Answer 2

The difference is not between "real" and "user"; the numbers are also in a different order.

The difference is between "real" and "total", and there isn't one. They're just different ways of saying the same thing: total, wall-clock, real-world time to execute your program, including all user code, system calls and (crucially) any time that your CPU spent on other processes/tasks.