21 Language support library [language.support]

21.5 Start and termination [support.start.term]

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The header <cstdlib> declares the functions described in this subclause.
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[[noreturn]] void _Exit(int status) noexcept;
Effects: This function has the semantics specified in the C standard library.
Remarks: The program is terminated without executing destructors for objects of automatic, thread, or static storage duration and without calling functions passed to atexit() ([basic.start.term]).
The function _­Exit is signal-safe.
[[noreturn]] void abort() noexcept;
Effects: This function has the semantics specified in the C standard library.
Remarks: The program is terminated without executing destructors for objects of automatic, thread, or static storage duration and without calling functions passed to atexit() ([basic.start.term]).
The function abort is signal-safe.
int atexit(c-atexit-handler* f) noexcept; int atexit(atexit-handler* f) noexcept;
Effects: The atexit() functions register the function pointed to by f to be called without arguments at normal program termination.
It is unspecified whether a call to atexit() that does not happen before a call to exit() will succeed.
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The atexit() functions do not introduce a data race ([res.on.data.races]).
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Implementation limits: The implementation shall support the registration of at least 32 functions.
Returns: The atexit() function returns zero if the registration succeeds, nonzero if it fails.
[[noreturn]] void exit(int status);
Effects:
  • First, objects with thread storage duration and associated with the current thread are destroyed.
    Next, objects with static storage duration are destroyed and functions registered by calling atexit are called.215
    See [basic.start.term] for the order of destructions and calls.
    (Automatic objects are not destroyed as a result of calling exit().)216
    If control leaves a registered function called by exit because the function does not provide a handler for a thrown exception, std​::​terminate() shall be called ([except.terminate]).
  • Next, all open C streams (as mediated by the function signatures declared in <cstdio>) with unwritten buffered data are flushed, all open C streams are closed, and all files created by calling tmpfile() are removed.
  • Finally, control is returned to the host environment.
    If status is zero or EXIT_­SUCCESS, an implementation-defined form of the status successful termination is returned.
    If status is EXIT_­FAILURE, an implementation-defined form of the status unsuccessful termination is returned.
    Otherwise the status returned is implementation-defined.217
int at_quick_exit(c-atexit-handler* f) noexcept; int at_quick_exit(atexit-handler* f) noexcept;
Effects: The at_­quick_­exit() functions register the function pointed to by f to be called without arguments when quick_­exit is called.
It is unspecified whether a call to at_­quick_­exit() that does not happen before all calls to quick_­exit will succeed.
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The at_­quick_­exit() functions do not introduce a data race ([res.on.data.races]).
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The order of registration may be indeterminate if at_­quick_­exit was called from more than one thread.
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The at_­quick_­exit registrations are distinct from the atexit registrations, and applications may need to call both registration functions with the same argument.
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Implementation limits: The implementation shall support the registration of at least 32 functions.
Returns: Zero if the registration succeeds, nonzero if it fails.
[[noreturn]] void quick_exit(int status) noexcept;
Effects: Functions registered by calls to at_­quick_­exit are called in the reverse order of their registration, except that a function shall be called after any previously registered functions that had already been called at the time it was registered.
Objects shall not be destroyed as a result of calling quick_­exit.
If control leaves a registered function called by quick_­exit because the function does not provide a handler for a thrown exception, std​::​terminate() shall be called.
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A function registered via at_­quick_­exit is invoked by the thread that calls quick_­exit, which can be a different thread than the one that registered it, so registered functions should not rely on the identity of objects with thread storage duration.
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After calling registered functions, quick_­exit shall call _­Exit(status).
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The standard file buffers are not flushed.
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Remarks: The function quick_­exit is signal-safe when the functions registered with at_­quick_­exit are.
See also: ISO C 7.22.4
A function is called for every time it is registered.
Objects with automatic storage duration are all destroyed in a program whose main function contains no automatic objects and executes the call to exit().
Control can be transferred directly to such a main function by throwing an exception that is caught in main.
The macros EXIT_­FAILURE and EXIT_­SUCCESS are defined in <cstdlib>.