exit(0) 和 raise(SIGTERM) 有什么区别

Question

I am trying to terminate my app on some particular event. Why would one use exit(0) or raise(SIGTERM) over the other?

Also since exit(0) returns EXIT_SUCCESS to the host, what does SIGTERM do? Is it always failure?

Answer 1

exit causes the program to terminate with normal exit status, with value given by the argument to exit , in your case 0.

raise raises a signal, which may be caught. If it's not caught or blocked then the default action is carried out. For SIGTERM , the default action is abnormal termination, and the signal that caused it is visible in the program's exit status.

What consequences this has for iOS applications, I'm not sure.

Answer 2

Sending raise( SIGTERM ) by default causes an "abnormal termination", which means many things done in a normal program termination are not done. Per the C 11 standard's 7.22.4.4 The exit function

Description

2 The exit function causes normal program termination to occur. No functions registered by the at_quick_exit function are called. If a program calls the exit function more than once, or calls the quick_exit function in addition to the exit function, the behavior is undefined.

3 First, all functions registered by the atexit function are called, in the reverse order of their registration, except that a function is called after any previously registered functions that had already been called at the time it was registered. If, during the call to any such function, a call to the longjmp function is made that would terminate the call to the registered function, the behavior is undefined.

4 Next, all open streams with unwritten buffered data are flushed, all open streams are closed, and all files created by the tmpfile function are removed.

5 Finally, control is returned to the host environment. ...

None of that will happen if you call raise(SIGTERM) unless you add a signal handler that will somehow invoke exit() . And note that you can NOT simply call exit() directly from a signal handler as the exit() function is not async-signal-safe.

Note especially "all open streams with unwritten buffered data are flushed". If that's not done, you risk losing data.

And, as noted, any temporary files created by your program will not be cleaned up.

In C++ code, objects with static storage duration are destroyed in a standard program termination. That will not happen in an abnormal termination caused by raise( SIGTERM ) . So any cleanup that those objects perform in their destructors will not be done.