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The C99 {{exit()}} function is used for normal program termination. Nested calls to {{exit()}} result in [undefined behavior|BB. Definitions#undefined behavior]. This can only occur when {{exit()}} is invoked from a function registered with {{atexit()}}, or when {{exit()}} is called from within a signal handler (see \[[SIG30-C. Call only asynchronous-safe functions within signal handlers]\]). |
No atexit() handler should terminate in any way other than by returning. It is important and potentially safety-critical for all the atexit() handlers to be allowed to perform their cleanup actions. This is particularly true because the main program doesn't always know about handlers that may have been installed by support libraries.
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