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The
program entry mechanism, which is the means by which the
main
function gains control, is system dependent. However, program
exit is not always system dependent, although it does have some implementation
dependencies.
One simple way to terminate execution of a C program
is for the
main
function to execute a
return
statement; another is for the
main
function to drop through its terminating brace. However, in many
cases, a more flexible program exit capability is needed. This capability
is provided by the
exit
function described
in this section. This function offers the advantage of allowing any function
(not just
main
) to terminate the program,
and it allows information to be passed to other programs. (footnote 1)
You can use the
atexit
function to define a function to be called during normal program termination,
either due to a call to
exit
or due to
return from the
main
function.
The
abend
and
abort
functions can also be used to terminate
execution of a C program. These functions cause abnormal termination, which
causes both library cleanup and user cleanup (defined by
atexit
routines) to be bypassed.
In some cases, it is useful for a program to pass control
directly to another part of the program (within a different function) without
having to go through a long and possibly complicated series of function returns.
The
setjmp
and
longjmp
functions
provide a general capability for passing control in this way.
You can use the SAS/C extension
blkjmp
to intercept calls to
longjmp
that cause the calling routine to be terminated. This is useful for functions
that allocate resources that must be released before the function is terminated.
You can also use
blkjmp
to intercept calls
to
exit
.
Note:
The
jump functions use a special type,
jmp_buf
,
which is defined in the
<setjmp.h>
header
file. ![[cautionend]](../common/images/cautend.gif)
Several of the program control functions have a special version for use in the Systems Programming Environment. See Implementation of Functions for more details.
The program control functions are
indep
feature, program execution can also be terminated by calling
the L$UEXIT routine from non-C code, as described in Appendix 5, "Using the
indep Option for Interlanguage Communication," in the
SAS/C Compiler and Library User's Guide. ![[arrow]](../common/images/fntarrow.gif)
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Copyright © 2001 by SAS Institute Inc., Cary, NC, USA. All rights reserved.