[vox-tech] Where setjmp/longjmp went after C
Jeff Newmiller
vox-tech@lists.lugod.org
Sat, 16 Mar 2002 13:25:59 -0800 (PST)
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The attached two files demonstrate a rudimentary "structured
setjmp/longjmp" that mimics the "exceptions" of Ada and C++ (and other
languages). I wrote an article about this in spring 1991 for C User's
Journal, and my bad luck was that two other people beat me to the punch,
so it never got published. What I have here is pulled from memory, but I
think it gets the idea across.
The real value of this technique comes into play when everyone uses the
same system... and you need language support to avoid certain problems
with auto variables... so I would only recommend using this if you are
stuck in C. :)
The basic idea is that you can detect certain problems deep in your
program, but if you want those pieces to be re-usable in, say, a GUI or
embedded environment, then you won't be able to report problems to the
user directly in those subroutines. The mid- or hi level portions of the
program may already be tied into the user interface, so having them pass
on the problem to the user in an environmentally appropriate way makes
sense. This technique is one way to propagate abnormal conditions out of
those re-usable routines.
Note that it should not be used in places where you expect to encounter
problems regularly... it is less efficient than simple tests on return
values, and you don't want all your program logic to depend on
exceptions... it gets hard to follow if you have a lot of kinds of
exceptions. However, they are useful when you have unusual problems that
low-level routines cannot handle themselves.
j1.c is the demonstration source... jbexcept.h are the macros to be shared
throughout all source files, and j1_nomacro.c is the de-macroized j1.c so
you can follow things as they are implemented. See the comment at the
beginning of j1.c for how to run it.
---------------------------------------------------------------------------
Jeff Newmiller The ..... ..... Go Live...
DCN:<jdnewmil@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go...
Live: OO#.. Dead: OO#.. Playing
Research Engineer (Solar/Batteries O.O#. #.O#. with
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