Catching termination of child process and system() call

[Geoff Clare]

In <12673:Feb1900:07:4691 at kramden.acf.nyu.edu> brnstnd at kramden.acf.nyu.edu (Dan Bernstein) writes:

>In article <2608 at root44.co.uk> gwc at root.co.uk (Geoff Clare) writes:
>> The discussion does have some relevance to 'C' since
>> it is about the format of the status returned by wait(),

>No. It has absolutely nothing to do with C. We just happen to be talking
>about it in C.

I noticed you chopped off an important piece of text when quoting me.
It referred to the system() function, which is defined by ANSI 'C'.
A discussion of how the return value of system() is interpreted certainly
is relevant to 'C', even if the discussion only involves how the value is
interpreted on UNIX systems.  Anyway, now the discussion has moved to
comp.unix.programmer, there's no point in continuing the argument over
whether it is relevant to comp.lang.c.

>> POSIX does not specify the precise encoding of information in the status
>> returned by wait(), system(), etc., so portable programs should not
>> rely on the traditional encoding Chris describes above.  Instead macros
>> are provided in <sys/wait.h> to extract the relevant data from the status:

>Wrong. A program written according to your advice is decidedly
>nonportable: it will work only on POSIX systems. A program written
>according to Chris's advice will work under System V, BSD, and most
>POSIX-based systems to boot. Someone who wants to plan for the future
>should conditionally compile the POSIX code, though of course he'll
>still have to use w & 0200 to get the core dump bit.

If you re-read more carefully what I wrote, you'll realise you've done me an
injustice.  I said "portable programs should not *rely* on the traditional
encoding Chris describes above."  I did *not* say they should instead use
*only* the POSIX macros, which is what you infer I said.

A program which wants to be portable both to POSIX systems and to
traditional systems would need to do something like this:

#include <sys/wait.h>
#ifndef WIFEXITED
#define WIFEXITED(s)	(((s) & 0xff) == 0)
#endif
#ifndef WEXITSTATUS
etc......

>Portability is defined by the real world, not a standards committee.

The two are not mutually exclusive - the POSIX standards are a part of
the real world.  Widely portable programs need to allow for both POSIX
systems and traditional systems.
-- 
Geoff Clare <gwc at root.co.uk>  (Dumb American mailers: ...!uunet!root.co.uk!gwc)
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