为什么在 execvp 之后我们需要子出口？

Question

I have been recently wondering why do we need to use exit after the execution of a child after performing execvp. An in depth explannation is welcome.

Answer 1

You do not need for the child to call exit() after execvp() , but it is often wise for you to ensure that it does so. So much so as to support giving that to novices as a rule.

When a call to execvp() or one of the other exec functions succeeds, it has the effect of replacing the currently-running process image with a new one. As a result, these functions do not return on success, and nothing that follows matters in that case. The issue, then, is entirely about what to do in the event that the exec* call fails .

If you do not exit the child in the event that an exec fails then it will continue running the code of the parent. That is rarely intended or wanted. It may do work that it was not intended to do, delay the parent (that is often wait() ing for it) by not exiting promptly, and eventually mislead the parent with an exit status that is not reflective of what actually happened.

All of that, and perhaps more, is addressed by ensuring that the control flow following an exec* call pretty quickly reaches program termination with a failure status (typically via _Exit() or _exit() ; less typically via exit() or abort() ). Depending on the circumstances, it may or may not be appropriate to emit a diagnostic message before exiting, or to perform some other kind of cleanup.