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From: dleigh@hplabsz.HPL.HP.COM (Darren Leigh)
Newsgroups: comp.sources.wanted,comp.lang.c,comp.sys.ibm.pc
Subject: Re: C / IBM REQUIREMENTS......
Message-ID: <735@hplabsz.HPL.HP.COM>
Date: Wed, 26-Aug-87 21:02:10 EDT
Article-I.D.: hplabsz.735
Posted: Wed Aug 26 21:02:10 1987
Date-Received: Sat, 29-Aug-87 06:13:58 EDT
References: <6050@ut-ngp.UUCP>
Reply-To: dleigh@hplabsz.UUCP (Darren Leigh)
Organization: Hewlett-Packard Laboratories
Lines: 34
Summary: peeking and poking from MSC 4.0
Xref: mnetor comp.sources.wanted:2048 comp.lang.c:3945 comp.sys.ibm.pc:7174

In article <6050@ut-ngp.UUCP> marshek@ut-ngp.UUCP (The Genie) writes:
>
>Anybody out there have any stuff to do a peek & poke function in C ?
>(The peek & poke of BASIC).

C does lots of interesting things with pointers so that is a good way
to start.  All you have to do is stuff an absolute address into a
pointer.  The real problem here is the brain-damaged Intel/IBM
architecture, but it can be done.  From Microsoft C 4.0 you can do the
following:

  Say you want to deal with a byte at location 0040:0049 that controls
the video mode.  A BASIC-like videomode = peek(address) would be done
like this:  videomode = *(char far *) 0x400049L;
This takes the absolute value 0040:0049 and casts it to a far pointer
to a character (or single byte).

  The code for poke operates similarly.  The BASIC command
poke(address,videomode) could be set up as:  
*(char far *) 0x400049L = videomode;  This again casts the absolute
address 0040:0049 to a pointer to char and stuffs the value in there.

This works from MSC 4.0, and may or may not work from other C's.  Try
playing around by setting far pointers to the absolute addresses that
you need.  If your C does not support far pointers and does not have a
way of changing the segment registers, you are on your own and will
have to play with assembly language.


BTW, I pulled these little examples from page 37 of the December 1986
issue of the Microsoft Systems Journal.

Darren Leigh
dleigh@hplabs.hp.com