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Groups > comp.lang.c > #176778
| From | Tim Rentsch <tr.17687@z991.linuxsc.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Libraries using longjmp for error handling |
| Date | 2023-09-29 21:56 -0700 |
| Organization | A noiseless patient Spider |
| Message-ID | <86cyy0fee5.fsf@linuxsc.com> (permalink) |
| References | (4 earlier) <871qejf62x.fsf@bsb.me.uk> <86y1gphiur.fsf@linuxsc.com> <877co9d8m2.fsf@bsb.me.uk> <86bkdlghqr.fsf@linuxsc.com> <8734ywbvek.fsf@bsb.me.uk> |
Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>
>> Ben Bacarisse <ben.usenet@bsb.me.uk> writes:
>>
>> [..how should errors be handled..]
>>
>>> How would you prefer these sorts of thing to be signalled?
>>
>> Let me give just one example.
>>
>> I wrote some code not long ago to add a value to a set of values,
>> where the set is represented using a recursive binary tree structure
>> (like red-black trees, but a little different). Usually we may
>> expect that a request to add a value would offer a value not already
>> included in the set, but certainly it can happen that there is a
>> call to add a value that is already included, in which case the top
>> level return value should be the original tree structure.
>>
>> I thought it would be easier to write a simple recursive routine
>> that assumes the to-be-added value is not yet included in the set,
>> and if that assumption is violated raise an exception that is caught
>> at the outermost level and simply returns the original argument tree
>> value. Certainly the code could have been written to handle the
>> already-present situation at each level of the recursion, but it was
>> much easier and much cleaner to handle it by raising an exception.
>
> This is one of those cases where I just have to take your word for it,
> (and I am happy to do that).
Responding here to just this one part.
Here is a simpler version of the code, for an ordinary
binary tree, and without any rebalancing:
module TreeSet = struct
type 'a treeset = Empty | Node of 'a treeset * 'a * 'a treeset
exception Present
let add tree element =
let rec add t e =
match t with
| Empty -> Node( Empty, e, Empty )
| Node( a, v, b ) ->
if e < v then Node( add a e, v, b ) else
if e > v then Node( a, v, add b e ) else
raise Present
in
try add tree element with Present -> tree
end
Transliterating that into C, the central functions might look like
this (I have left out the type definition and the constructor
function used to build a new node value):
static Tree add( jmp_buf, Tree, double );
static Tree raise_present( jmp_buf );
static Tree new_node( Tree, double, Tree );
Tree
add_element( Tree tree, double new_element ){
jmp_buf jb;
if( setjmp( jb ) ) return tree;
return add( jb, tree, new_element );
}
Tree
add( jmp_buf jb, Tree t, double d ){
return
! t ? new_node( 0, d, 0 )
: d < t->v ? new_node( add( jb, t->a, d ), t->v, t->b )
: d > t->v ? new_node( t->a, t->v, add( jb, t->b, d ) )
: /*********/ raise_present( jb );
}
Tree
raise_present( jmp_buf jb ){
longjmp( jb, 1 );
}
Of course it's unlikely that sets would be implemented this way
in C, but that's not the point; the point is that exceptions
can result in code that is cleaner and easier to understand
than an alternate approach where return values would have to
be checked at every level.
(Incidentally, I want to acknowlege you comment about taking my
word for the result. I still thought it would be good to give
a concrete example, even if it is a very simplified one.)
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Libraries using longjmp for error handling (was: Re: More on NNTP testing) Blue-Maned_Hawk <bluemanedhawk@invalid.invalid> - 2023-09-27 22:52 +0000
Re: Libraries using longjmp for error handling (was: Re: More on NNTP testing) Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2023-09-28 08:19 +0800
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-28 02:18 +0100
Re: Libraries using longjmp for error handling Blue-Maned_Hawk <bluemanedhawk@invalid.invalid> - 2023-09-28 22:30 +0000
Re: Libraries using longjmp for error handling scott@slp53.sl.home (Scott Lurndal) - 2023-09-28 22:33 +0000
Re: Libraries using longjmp for error handling Anton Shepelev <anton.txt@gmail.moc> - 2023-09-29 01:41 +0300
Re: Libraries using longjmp for error handling scott@slp53.sl.home (Scott Lurndal) - 2023-09-28 23:45 +0000
Re: Libraries using longjmp for error handling Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-28 17:35 -0700
Re: Libraries using longjmp for error handling David Brown <david.brown@hesbynett.no> - 2023-09-29 16:49 +0200
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-28 18:24 -0700
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-29 03:19 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-29 07:46 -0700
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-29 21:02 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-29 21:56 -0700
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-10-01 00:06 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-30 20:35 -0700
Re: Libraries using longjmp for error handling Anton Shepelev <anton.txt@gmail.moc> - 2023-10-01 14:44 +0300
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-10-01 15:45 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-10-01 09:28 -0700
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-10-01 20:49 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-10-02 02:31 -0700
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-10-02 23:55 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-10-03 05:01 -0700
Re: Libraries using longjmp for error handling Anton Shepelev <anton.txt@gmail.moc> - 2023-09-29 23:58 +0300
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-10-01 02:52 -0700
Re: Libraries using longjmp for error handling Anton Shepelev <anton.txt@gmail.moc> - 2023-10-01 14:33 +0300
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-28 01:48 +0100
Re: Libraries using longjmp for error handling (was: Re: More on NNTP testing) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-28 05:11 +0000
Re: Libraries using longjmp for error handling (was: Re: More on NNTP testing) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-28 06:26 +0000
Re: Libraries using longjmp for error handling (was: Re: More on NNTP testing) Anton Shepelev <anton.txt@gmail.moc> - 2023-09-28 16:02 +0300
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-28 14:44 +0100
Re: Libraries using longjmp for error handling Anton Shepelev <anton.txt@gmail.moc> - 2023-09-28 18:31 +0300
Re: Libraries using longjmp for error handling Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-28 16:43 +0000
Re: Libraries using longjmp for error handling scott@slp53.sl.home (Scott Lurndal) - 2023-09-28 17:00 +0000
Re: Libraries using longjmp for error handling Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-28 17:16 +0000
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-28 19:38 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-28 16:05 -0700
Re: Libraries using longjmp for error handling Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-29 00:26 +0000
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-28 23:20 -0700
Re: Libraries using longjmp for error handling Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-28 18:31 -0700
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-29 03:24 +0100
Re: Libraries using longjmp for error handling Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-29 03:12 +0000
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-28 22:45 -0700
Re: Libraries using longjmp for error handling Spiros Bousbouras <spibou@gmail.com> - 2023-09-29 12:02 +0000
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-29 08:10 -0700
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-29 17:03 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-29 10:15 -0700
Re: Libraries using longjmp for error handling gazelle@shell.xmission.com (Kenny McCormack) - 2023-09-29 17:17 +0000
Re: Libraries using longjmp for error handling Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-29 18:53 +0000
Re: Libraries using longjmp for error handling Anton Shepelev <anton.txt@gmail.moc> - 2023-09-29 18:11 +0300
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-29 10:20 -0700
Re: Libraries using longjmp for error handling Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-29 11:30 -0700
Re: Libraries using longjmp for error handling Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-29 18:31 +0000
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-28 19:27 +0100
Re: Libraries using longjmp for error handling Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-28 20:24 +0000
Re: Libraries using longjmp for error handling Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-28 22:23 +0100
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-28 15:43 -0700
Re: Libraries using longjmp for error handling Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-28 23:11 +0000
Re: Libraries using longjmp for error handling Anton Shepelev <anton.txt@gmail.moc> - 2023-09-29 17:23 +0300
Re: Libraries using longjmp for error handling Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-29 08:19 -0700
Re: Libraries using longjmp for error handling David Brown <david.brown@hesbynett.no> - 2023-09-28 21:57 +0200
Re: Libraries using longjmp for error handling Richard Kettlewell <invalid@invalid.invalid> - 2023-09-30 09:37 +0100
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