Terminate calling process
Terminates the process normally, performing the regular cleanup for terminating programs.
Normal program termination performs the following (in the same order):
- Objects associated with the current thread with thread storage duration are destroyed (C++11 only).
- Objects with static storage duration are destroyed (C++) and functions registered with atexit
- All C streams (open with functions in <cstdio>) are closed (and flushed, if buffered), and all files created with tmpfile
- Control is returned to the host environment.
Note that objects with automatic storage are not destroyed by calling
exit (C++).
If status is zero or EXIT_SUCCESS, a
successful termination status is returned to the host environment.
If status is EXIT_FAILURE, an
unsuccessful termination status is returned to the host environment.
Otherwise, the status returned depends on the system and library implementation.
exit()和return的区别：
按照ANSI C，在最初调用的main()中使用return和exit()的效果相同。
但要注意这里所说的是“最初调用”。如果main()在一个递归程序中，exit()仍然会终止程序；但return将
控制权移交给递归的前一级，直到最初的那一级，此时return才会终止程序。return和exit()的另一个区别
在于，即使在除main()之外的函数中调用exit()，它也将终止程序。
