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From: kevvy@AMSAA.ARPA (RAMD-SUM)
Newsgroups: net.lang.c
Subject: a.out.h,adventure operating systems, JMP indirects, C for Apples, etc..
Message-ID: <11664@brl-tgr.ARPA>
Date: Thu, 18-Jul-85 11:06:29 EDT
Article-I.D.: brl-tgr.11664
Posted: Thu Jul 18 11:06:29 1985
Date-Received: Sat, 20-Jul-85 09:56:01 EDT
Sender: news@brl-tgr.ARPA
Lines: 52


  Basically, I'm writing a unix-like operating system on a micro to base
an adventure-type game on.  I'm doing preliminary work on the unix system
itself, and the operating system seems to intercept many of the things I
must do.  The problem is as follows:  To load in the desired procedure
(function) into the memory swapping space, call it, free the swap space,
and continue this indefinitely.  I've written a small program segment,
which SHOULD work, but appears not to.  

----------------------------------------------------------------------

#include <stdio.h>

static char *filename = "file.data";

main()
{
int call();
char s[2048],*s2;
FILE *fp;

if ( fp=fopen( filename,"r" ) )
  {
  s2 = s;
  while ( ( *(s2++) = getc(fp) ) != EOF);
  
  call( s );
  }
else printf("Can't open %s\n",filename);
}

call(p)
/* calls function located at pointer given */
int (*p) ();
{
  (*p) ();    /* basically a JMP indirect op */
}

---------------------------------------------------------------------

It loads in an executable file (file.data), and calls the location it was 
loaded into.  The operating system responds with "illegal instruction", 
meaning, as I see it, that unix pre-pends some junk at the beginning of 
the file which cannot be executed.  As I see it it's the junk from the 
/usr/include/aout.h file.  Is this common in most C environments?
Keeping info about a file SHOULD be kept in the directory, not in the file 
itself.  Would anyone know how to get around this problem in a "standard"
sort of way?   Also, I'm looking for a good ( but cheap ) copy of C for
the Apple ][ computer and any help in that quest would be greatly ap-
preciated as well...

						kevvy@amsaa.arpa