drears@ardec.ARPA (FSAC) (10/29/86)
We are running HP-UP UNIX on a Hewlett-Packard System 9050. THe
HP-UP is SYSV look alike with shared memory operations. I am trying to
compile a program that allows users to talk with each other. This
program is similiar to talk except that is uses shared memory. It
compiles and works under a AT&T SYS5 release 2. However when I compile
it under hp-UNIX I get the following error messages:
rap.c, line 310: warning: absolute pointer used
rap.c, line 369: warning: absolute pointer used
Lines 310 & 369 are the exact same and look like this:
if ( shmaddr EQ (char *) -1 ) {
Can anyone shed some light on what is meant by an absolute
pointer. I am assuming it doesn't like the cast but I am not sure.
Incidently the "EQ" is defined as "==".
Dennishenry@utzoo.UUCP (Henry Spencer) (10/31/86)
> rap.c, line 310: warning: absolute pointer used > > if ( shmaddr EQ (char *) -1 ) { The compiler is trying to warn you, in a somewhat cryptic way, that casting any integer except the constant 0 into a pointer is a machine-dependent, unportable, and dangerous operation. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,decvax,pyramid}!utzoo!henry
levy@ttrdc.UUCP (Daniel R. Levy) (11/02/86)
In article <7267@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes: >> rap.c, line 310: warning: absolute pointer used >> >> if ( shmaddr EQ (char *) -1 ) { > >The compiler is trying to warn you, in a somewhat cryptic way, that casting >any integer except the constant 0 into a pointer is a machine-dependent, >unportable, and dangerous operation. >-- > Henry Spencer @ U of Toronto Zoology > {allegra,ihnp4,decvax,pyramid}!utzoo!henry However, in SysV the shmat(2) call returns (char *) -1 in case of error. I'll bet a doughnut that this is where shmaddr is coming from. Is anyone aware of any computer where this would not work as intended (thus, couldn't support full SysV)? It could be argued that NULL (i.e., 0, with its already agreed-upon special-caseness) would have been better (more portable?) but it's too late now and I've never heard where it hurt anyone either. -- ------------------------------- Disclaimer: The views contained herein are | dan levy | yvel nad | my own and are not at all those of my em- | an engihacker @ | ployer or the administrator of any computer | at&t computer systems division | upon which I may hack. | skokie, illinois | -------------------------------- Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa, go for it! allegra,ulysses,vax135}!ttrdc!levy
kah@hpfclq.HP.COM (Kathy Harris) (11/03/86)
>rap.c, line 310: warning: absolute pointer used >Lines 310 & 369 are the exact same and look like this: > if ( shmaddr EQ (char *) -1 ) { The HP9000 Series 500 C compiler issues this warning whenever an integer constant other than 0 is used as a pointer. Its intent is to flag statements that are machine dependent in code ported from other systems. Kathy Harris Hewlett Packard, Systems Software Operation {hplabs, ihnp4}!hpfcla!kah
guy@sun.uucp (Guy Harris) (11/06/86)
> > if ( shmaddr EQ (char *) -1 ) { > > > The HP9000 Series 500 C compiler issues this warning whenever an > integer constant other than 0 is used as a pointer. Its intent > is to flag statements that are machine dependent in code ported > from other systems. Unfortunately, the shared memory system calls in System V have a *really poor* convention for indicating errors; they *should* have returned NULL, but instead they return -1 cast to "char *". The intent may have been to make them "just like" system calls that return integral values, but this doesn't buy you anything (other than being able to use the same user-mode stub code for calls that return integral values and that use pointers, but this only saves you a handful of bytes). As such, while this code is flagging code that may be machine dependent, you can't do anything about it (at least not while remaining compatible with the SVID), so the warning is merely noise. The compiler should NOT issue this warning if -1 is being cast to a pointer. -- Guy Harris {ihnp4, decvax, seismo, decwrl, ...}!sun!guy guy@sun.com (or guy@sun.arpa)