🚀 go-pugleaf

In article <9208311827.AA10025@ucbvax.Berkeley.EDU> JENNIFER@TOROLAB6.VNET.IBM.COM ("Jennifer Hamilton") writes:
>( ... also posted to comp.lang.c)

In order to do that, you should edit the "Newsgroups:" line in the header
to say "Newsgroups: comp.std.c,comp.lang.c" instead of posting two
separate articles.

>In the ANSI standard under the description of the signal function,
>(section 4.7.1.1) it states the following:
>   "The function func may terminate by executing a return statement or
>   by calling the abort, exit, or longjmp functions.  If func executes a
>   return statement and the value of sig was SIGFPE or any other
>   implementation-defined value corresponding to a computational
>   exception, the behaviour is undefined.  Otherwise, the program will
>   resume execution at the point it was interrupted.  If the signal
>   occurs other than as the result of calling the abort or raise
>   function, the behaviour is undefined if the signal handler calls any
>   function in the standard library other than the signal function
>   itself ..."
>The last sentence implies that you can't call any library functions
>(such as longjmp, abort or exit) from within the signal handler unless
>the signal was explicitly raised through raise or abort.

That is correct.  (However, even when the standard explicitly leaves the
behavior undefined, an implementation is still allowed to define an
extension if it wishes, and a non-strictly conforming program is allowed
to take advantage of the extension, though it won't be portable.)

>But the first three sentences imply that you can.

Well, yes and no.  It does seem worded to raise false hopes before quashing
them.  However, it doesn't exactly say that func may call abort, exit, or
longjmp under all circumstances.  The only "standard" circumstance under
which a signal may be received is due to calling abort or raise, and under
this circumstance, there are four defined methods of exiting.  If a signal
is received due to implementation extensions, then the standard says that
the implementation still has to allow an ordinary return statement, but
doesn't have to allow other means of exit from the handler.

Now, one might wonder if SIGPFE, SIGILL, SIGINT, SIGSEGV, or SIGTERM might
also be "standard" circumstances for signals to be received.  Well, the
standard says "An implementation need not generate any of these signals,
except as a result of explicit calls to the raise function."  So even though
these macros exist, they do not have "standard" defined meanings.
--
Norman Diamond       diamond@jit081.enet.dec.com
If this were the company's opinion, I wouldn't be allowed to post it.
"Yeah -- bad wiring.  That was probably it.  Very bad."