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`atexit'--request execution of functions at program exit

     #include <stdlib.h>
     int atexit (void (*FUNCTION)(void));
You can use `atexit' to enroll functions in a list of functions that
will be called when your program terminates normally.  The argument is
a pointer to a user-defined function (which must not require arguments
and must not return a result).
   The functions are kept in a LIFO stack; that is, the last function
enrolled by `atexit' will be the first to execute when your program
   There is no built-in limit to the number of functions you can enroll
in this list; however, after every group of 32 functions is enrolled,
`atexit' will call `malloc' to get space for the next part of the list.
 The initial list of 32 functions is statically allocated, so you can
always count on at least that many slots available.
`atexit' returns `0' if it succeeds in enrolling your function, `-1' if
it fails (possible only if no space was available for `malloc' to
extend the list of functions).
`atexit' is required by the ANSI standard, which also specifies that
implementations must support enrolling at least 32 functions.
   Supporting OS subroutines required: `close', `fstat', `isatty',
`lseek', `read', `sbrk', `write'.