.\" This file is part of the Public Domain C Library (PDCLib).
.\" Permission is granted to use, modify, and / or redistribute at will.
.\"
.Dd
.Dt atexit 3
.Os
.\"
.Sh NAME
.Nm atexit
.Nd registration of functions to be invoked before process termination
.\"
.Sh SYNOPSIS
.In stdlib.h
.Fn "int atexit" "void (*handler)(void)"
.Fn "int at_quick_exit" "void (*handler)(void)" 
(C11, C++11)
.\"
.Sh DESCRIPTION
These functions register a function to be called when the corresponding process
exit function is invoked. For
.Fn atexit 
the function will be invoked when the process is terminated by calling
.Fn exit ;
for
.Fn at_quick_exit
the function will be invoked when the process is terminated by calling
.Fn quick_exit .
.\"
.Pp
These functions are used in order to permit a program to perform actions before
a process is terminated; for example, releasing an interprocess semaphore. 
Special care should be taken when writing 
.Fn at_quick_exit
handlers; the purpose of 
.Fn quick_exit
is to support the abandonning of a process when normal process termination might
not be possible; at_quick_exit handlers should therefore be used sparingly and
only when their use is essential.
.\"
.Pp
The standard guarantees that 
.Fn atexit
and
.Fn at_quick_exit
may each be called at least 32 times successfully.
.\"
.Pp
.Fn atexit 
and
.Fn at_quick_exit
handlers are called in reverse order of the order they were registered in. For
precise details of their ordering, see
.Xr exit 3 .
.\"
.Pp
The result of exiting from a handler registered with
.Fn atexit
or
.Fn at_quick_exit
by use of 
.Fn longjmp
is undefined. If any function or destructor invoked by
.Fn exit
or
.Fn quick_exit
should throw, 
.Fn std::terminate
is invoked.
.\"
.Pp
Undefined behaviour results if an 
.Fn atexit
or
.Fn at_quick_exit
handler calls
.Fn exit
or
.Fn quick_exit . 
.\"
.Sh RETURN VALUES
Returns 0 to indicate success; nonzero returns indicate failure.
.\"
.Sh ERRORS
No errors are defined
.\"
.Sh SEE ALSO
.Xr abort 3
.Xr exit 3
.Xr quick_exit 3
.Xr _Exit 3
.\"
.Sh STANDARDS
.Fn atexit
is first defined in
.St -isoC-90 ;
.Fn at_quick_exit
was introduced in
.St -isoC-2011 
and
ISO/IEC 14882:2011 "C++ 2011" .