17 Language support library [support]

17.5 Startup and termination [support.start.term]

[Note 1:

The header <cstdlib> declares the functions described in this subclause.

— end note]

[[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 .

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[[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 .

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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.

[Note 2:

The atexit() functions do not introduce a data race ([res.on.data.races]).

— end note]

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.

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[[noreturn]] void exit(int status);

Effects:

(9.1)
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.195

See [basic.start.term] for the order of destructions and calls.

(Objects with automatic storage duration are not destroyed as a result of calling exit().)196
If a registered function invoked by exit exits via an exception, the function std::terminate is invoked ([except.terminate]).
(9.2)
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.
(9.3)
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.197

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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.

[Note 3:

The at_quick_exit() functions do not introduce a data race ([res.on.data.races]).

— end note]

[Note 4:

The order of registration could be indeterminate if at_quick_exit was called from more than one thread.

— end note]

[Note 5:

The at_quick_exit registrations are distinct from the atexit registrations, and applications might need to call both registration functions with the same argument.

— end note]

Implementation limits: The implementation shall support the registration of at least 32 functions.

Returns: Zero if the registration succeeds, nonzero if it fails.

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[[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 a registered function invoked by quick_exit exits via an exception, the function std::terminate is invoked ([except.terminate]).

[Note 6:

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 cannot rely on the identity of objects with thread storage duration.

— end note]

After calling registered functions, quick_exit shall call _Exit(status).

Remarks: The function quick_exit is signal-safe when the functions registered with at_quick_exit are.