OT: Requesting C advice

[Les]

On Thu, 2007-05-31 at 18:44 -0500, Mike McCarty wrote:
> Les Mikesell wrote:
> > Mike McCarty wrote:
> > 
> 
> [Les wrote about "older" compilers]
> 
> >> Older? ANSI C is since 1989. I guess one could characterize 19 years
> >> as "older". :-)
> > 
> > 
> > C was old before ANSI came along.  Maybe we could revive the discussion 
> > of why "abcd"[2] must evaluate to 'c'.
> 
> I wasn't explicit enough, I guess. I wouldn't characterize
> 19 years as "older", but rather as "antique" or "ancient"
> in this context. I was objecting to using too weak a word,
> not too strong a word :-)
> 
I'm sorry, I don't think of myself as antique or ancient.  You assume
that all C compilers are ANSI compliant.  They are not.  K&R was around
a long time before the standards committee got involved.  And although
the standard may have been generated in 1989, Microsoft didn't implement
the ANSI standard for several years after that, and then failed some of
the standard tests.  SUN's compiler was not ANSII compliant until about
1994 or so.  There are many compilers out there, and most are probably
not fully compliant either.  AND I do know that the variables are not
initialized in many compilers.  I have fixed code for many, many people.
I know why their programs failed.  I also know that C uses a pushdown
stack for variables in subroutines.  You can check it out with a very
simple program using pointers:

    #include <sttlib.h>
    
    int i,j,k;
    
    main()
    {
        int mi,mj,mk;
        int *x;
        mi=4;mj=5;mk=6;
        x=&mk;
        printf ("%d  %d  %d\n",*x++,*X++;*X++);
        x=&i;
        printf ("%d  %d  %d\n",*x++,*x++,*x++);
        i-1;j=2;k=3;
        printf ("%d  %d  %d\n",*x++,*x++,*x++);
  )

Just an exercise you understand.  compile and run this with several c
packages, or if the package you choose supports it, have it compile K&R.
and try it.

I cannot vouch for every compiler, only Microsoft, Sun, and Instant C
off the top of my head.  I have used a few other packages as well.  But
any really good programmer NEVER relies on system initialization.  It is
destined to fail you at bad times.  One case is as has been pointed out
here, that NULL is sometimes 0, sometimes 0x80000000, and sometimes
0xffffffff.  Even NULL as a char may be 0xFF 0xFF00 or 0x8000 depending
on the implementation.  But strings always end in a character NULL or
0x00 for 8 bit ascii, if you use GNU, Microsoft, or Sun C compilers.
They may do otherwise on some others.  It can byte (;-) you if you are
not careful.

    And since that is so, how are those variables initialized? and to
what value?  What is a pointer set to when it is intialized.  Hint, on
Cyber the supposed default for assigned pointers used to the the address
of the pointer.  Again, system dependencies may get you.

    And those systems that used the first location to store the return
address are not re-entrant, without other supporting code in the
background.  I think I used one of those once as well.

    PS.  A stack doesn't necessarily mean a processor call and return
stack.  It is any mechanism of memory address where the data is applied
to the current location, then the pointer incremented (or decremented
depending on the architecture).

Regards,
Les H