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A nested call to an exit function is undefined behavior. (see See undefined behavior 182.) . This behavior can occur only when an exit function is invoked from an exit handler or when an exit function is called from within a signal handler. (see See SIG30-C. Call only asynchronous-safe functions within signal handlers.).
If a call to the longjmp() function is made that would terminate the call to a function registered with atexit(), the behavior is undefined.
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