Very Computer

The C standard dictates that SEEK_SET, SEEK_CUR and SEEK_END (among others)  
must be #defined in stdio.h.  This is not a POSIX requirement.  The only  
POSIX constraints on stdio.h are that it must #define L_ctermid and  
STREAM_MAX and declare fdopen() and fileno() if _POSIX_SOURCE is #defined.  
It may optionally #define L_cuserid if _POSIX_SOURCE is #defined.

POSIX 1003.1 _does_ however, require that unistd.h #define SEEK_SET &c if  
_POSIX_SOURCE is #defined.  Thus, if you desire POSIX conformance, #include  
unistd.h.

Quote:> Sometimes, it's not defined at all.
> GNU, for example, puts it in 'unistd.h'.  The headers in SunOS 4.1.3 don't
> define it at all, and Centerline's products define it in 'stdio.h'.

Are you sure about the SunOS headers?  Here's a test I ran on my SPARC at  
work:

% fgrep SEEK_SET /usr/include/unistd.h
#ifndef SEEK_SET
#define SEEK_SET        0       /* Set file pointer to "offset" */
% uname -a
SunOS epimbe 4.1.1 1 sun4c

Perhaps they've moved unistd.h to /usr/5include since 4.1.1??

Quote:> As a result, the code ends up littered with an incomprehensible mess of
> #ifdef's and #defines, to hack around the peculiarities of each
> environment.

I do agree on this, and am rapidly tiring of system dependencies being  
handled by #ifdefs.

I've found the "POSIX Programmer's Guide" (Donald Lewine, O'Reilly, ISBN  
0-937175-73-0) to be priceless.  I strongly recommend this book to anyone  
using C, whether they be UNIX programmers or not (but particularly if they  
are).  It not only helps understand "what is defined where and by which  
standard", but also helps programmers to "Do the Right Thing" by clarifying  
what is POSIX conformant and what is historical baggage.

--
-----------------------------------------------------------------------------
Jim Vlcek                         UNIX for $166!
uunet!molly!vlcek                 Novell UnixWare from Information Foundation

Quote:>Perhaps they've moved unistd.h to /usr/5include since 4.1.1??

Nope:

        bootme$ egrep SEEK_SET /usr/include/unistd.h
        #ifndef SEEK_SET
        #define SEEK_SET        0       /* Set file pointer to "offset" */
        bootme$ uname -a
        SunOS bootme 4.1.3 6 sun4m

Quote:uunet!molly!vlcek (Jim Vlcek) writes:
>I do agree on this, and am rapidly tiring of system dependencies being  
>handled by #ifdefs.

        Speeking of which, is there a filter program that will output C
code with all the undefined portions removed? This would sure make
reading through code written to run on a million systems easier to read.

--
John Henders       GO/MU/E d* -p+ c+++ l++ t- m--- s/++ g+ w+++ -x+

Try cc with the options -E or -P.

--
|   Holger Uhr   ***   Pohlweg 60   ***   33098 Paderborn   ***   Germany   |

|How to become immortal: Read this signature tomorrow and follow its advice.|

I don't know of a program, but then, you don't need one.  Run the code through
a C compiler, and specify that you only want the code preprocessed.  Most C
compilers have an option like this, including Microsoft's.

--- Chris

===============================================================================
Christopher J. Nielsen

Student                            |  Junior Software Engineer
Rochester Institute of Technology  |  Northern Telecom - Rochester, New York

[Opinions expressed here may not represent those of my organizations.]

The code resulted after preprocessing is almost illegible, since _all_
the macros have been substituted. I wouldn't enjoy looking at something
like this, which is much worse than the original file, full of #ifdef's.

Dan
--
Dan Pop
Tel:   +41.22.767.2335

Mail:  CERN - PPE, Bat. 21 1-023, CH-1211 Geneve 23, Switzerland

Quote:>>        Speeking of which, is there a filter program that will output C
>>code with all the undefined portions removed? This would sure make
>>reading through code written to run on a million systems easier to read.

Yes.  There is a program called "unifdef" which does exactly what you
want.  It was contributed to the 4BSD, so it should be available at
various ftp sites (e.g., ftp.uu.net).

Quote:>I don't know of a program, but then, you don't need one.  Run the code through
>a C compiler, and specify that you only want the code preprocessed.  Most C
>compilers have an option like this, including Microsoft's.

If your goal is to *read* the program, having the C preprocessor replace
all symbolic constants with the actual values is *probably* not ideal.

Conrad

    As someone pointed out to me in e-mail, however, this strips out
comments and defines, except for rare compilers, of which gcc is not
one.  I think, for me, the lack of these would make the source less
readable than the original clutter.

--
John Henders       GO/MU/E d* -p+ c+++ l++ t- m--- s/++ g+ w+++ -x+

|>

|> >>
|> >>  Speaking of which, is there a filter program that will output C
|> >>code with all the undefined portions removed? This would sure make
|> >>reading through code written to run on a million systems easier to read.
|>
|> >I don't know of a program, but then, you don't need one.  Run the code through
|> >a C compiler, and specify that you only want the code preprocessed.  Most C
|> >compilers have an option like this, including Microsoft's.
|>
|>     As someone pointed out to me in e-mail, however, this strips out
|> comments and defines, except for rare compilers, of which gcc is not
|> one.  I think, for me, the lack of these would make the source less
|> readable than the original clutter.

Emacs has a hideifdef mode. This will hide any conditionally compiled bits that you wish to hide.

It works as follows. This code

#ifdef HIDDEN
if(a > b)
{
#endif
        a += b;
#ifdef HIDDEN

Quote:}

#endif

after hiding the block HIDDEN shows:

#ifdef HIDDEN ...
#endif
        a += b;
#ifdef HIDDEN ...
#endif

Derek
--
"When a man is tired of Ankh-Morpork, he is tired of ankle-deep slurry."
        -- (Terry Pratchett, Mort)

The option -C used with the -E option tells the preprocessor not to discard
comments.

--
|   Holger Uhr   ***   Pohlweg 60   ***   33098 Paderborn   ***   Germany   |

|How to become immortal: Read this signature tomorrow and follow its advice.|

Holger Uhr writes
Here,s the command you have been looking for.
Most Unix systems with some BSD heritage contain a command called unifdef.
NeXT certainly has it, and SunOS has had through 4.1.x, not sure about
Solaris 2.x.

Here's the top of the man page:
==========
UNIFDEF(1)          UNIX Programmer's Manual           UNIFDEF(1)

NAME
     unifdef - remove ifdef'ed lines

SYNOPSIS
     unifdef [ -t -l -c -Dsym -Usym -idsym -iusym ] ...  [ file ]

DESCRIPTION
     Unifdef is useful for removing ifdef'ed lines from a file
     while otherwise leaving the file alone.  Unifdef is like a
     stripped-down C preprocessor: it is smart enough to deal
     with the nested ifdefs, comments, single and double quotes
     of C syntax so that it can do its job, but it doesn't do any
     including or interpretation of macros.  Neither does it
     strip out comments, though it recognizes and ignores them.
.....

Takis Mercouris

:       Speeking of which, is there a filter program that will output C
: code with all the undefined portions removed? This would sure make
: reading through code written to run on a million systems easier to read.

Try using the -E flag when compiling the source ... It will run the
source though cpp, resulting in the code applicable to your system ...

--> robert

Running your code through preprocessor (if possible, some compilers
have this step integrated) does "wonders" to a code readability.
On the other hand it is possible to find somewhere on the net a source
to a small utility called 'ifdef' which should do a required cleanup.

   Michal Jaegermann