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Newsgroups: comp.os.msdos.programmer,comp.answers,news.answers
Subject: comp.os.msdos.programmer FAQ part 2 of 4
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Archive-name: msdos-programmer-faq/part2
Last-modified: 24 Sep 1993
(continued from part 1) (no warranty on the code or information)
If the posting date is more than six weeks in the past, see instructions
at the end of this article for how to get an updated copy.
Copyright (C) 1993 Stan Brown, Oak Road Systems. All rights reserved.
section 1. General questions
============================
Subject: 101. Why won't my code work?
First you need to try to determine whether the problem is in your
use of the programming language or in your use of MSDOS and your PC
hardware. (Your manual should tell you which features are standard
and which are vendor- or MSDOS- or PC-specific. You _have_ read
your manual carefully, haven't you?)
If the feature that seems to be working wrong is something related
to your PC hardware or to the internals of MS-DOS, this group is the
right place to ask. (Please check this FAQ list first, to make sure
your question isn't already answered here.)
On the other hand, if your problem is with the programming language,
the comp.lang hierarchy (including comp.lang.pascal and comp.lang c)
is probably a better resource. Please read the other group's FAQ
list thoroughly before posting. (These exist in comp.lang.c,
comp.lang.c++, comp.lang.modula3, comp.lang.lisp, comp.lang.perl;
they may exist in other groups as well.) It's almost never a good
idea to crosspost between this group and a language group.
Before posting in either place, try to make your program as small as
possible while still exhibiting the bad behavior. Sometimes this
alone is enough to show you where the trouble is. Also edit your
description of the problem to be as short as possible. This makes
it look more like you tried to solve the problem on your own, and
makes people more inclined to try to help you. See later in this
section for some important netiquette tips.
Subject: 102. What is this newsgroup about?
(rev: 11 Sep 1993) comp.os.msdos.programmer (comp.sys.ibm.pc.programmer
until September 1990) concerns programming for MS-DOS systems. The
article "USENET Readership report for Aug 93" in news.lists shows
78,000 readers of this newsgroup worldwide. Traffic (exclusive of
crossposts) was 813 articles aggregating 1604 Kbytes.
Much of our traffic is about language products (chiefly from Borland
and Microsoft). More programming topics focus on C than on any one
other language, but we are not just for C programmers (see next Q).
Since most MS-DOS systems run on hardware that is roughly compatible
with the IBM PC, on Intel 8088, 80188, or 80x86 chips, we tend to
get a lot of questions and answers about programming other parts of
the hardware.
Subject: 103. Is comp.os.msdos.programmer just for C programmers?
(new: 12 Aug 1993) No, it is for all programmers who to share
information about programming in MS-DOS. Programs and questions are
also posted in Pascal, assembly, and other languages (including
MS-DOS batch programming.)
Why does the newsgroup seem to be so C-oriented sometimes? There
are two reasons. First, comp.lang.c and comp.lang.pascal have
evolved in different directions. comp.lang.pascal welcomes
vendor-specific discussion, such as Turbo Pascal. Since so many of
TP's features are tailored to programming on PCs and in MS-DOS,
Turbo Pascal programmers tend to find DOS questions welcomed there,
so that comp.os.msdos.programmer gets less of the "DOS in Turbo
Pascal" traffic. On the other hand, comp.lang.c has stayed closer
to talking only about the C language, and vendor-specific or
operating-system-specific questions are not welcome. This tends to
push questions about disks, DOS file structure, video, the keyboard,
TSRs, etc. to c.o.m.p even when those programs are written in C.
This FAQ is definitely C-oriented, not because that's necessarily
best but because the original editor tried to stick to what he could
verify personally. As a C programmer (with some assembler), he
could most carefully verify solutions in C or assembler. He felt
that short, clear programs could be published in just one language
and programmers could translate them into their languages of choice.
But the FAQ list also contains several long programs written only in
C; this is a defect with no obvious remedy. Most answers that point
to source code at archive sites include both C- and Pascal-language
source when available; please draw any omissions to the editor's
attention.
Subject: 104. What's the difference from comp.sys.ibm.pc.programmer?
c.s.i.p.programmer is the old name of comp.os.msdos.programmer, and
has been obsolete since September 1990. However, many systems have
not removed the old group, or have removed it but aliased it to the
new name. This means that some people still think they're posting
to c.s.i.p.programmer even though they're actually posting to
c.o.m.programmer.
You can easily verify the non-existence of c.s.i.p.programmer by
reference to the "List of Active Newsgroups" posted to news.groups.
It's available as /pub/usenet/news.answers/active-newsgroups/part1
from the archives (see "Where are FAQ lists archived?" in section C,
"More information").
Subject: 105. Is comp.os.msdos.programmer available as a mailing list?
(new: 2 Feb 1993) Sorry, no.
Subject: 106. What's this "netiquette"?
(new: 7 Aug 1993) Netiquette is good Usenet etiquette. It includes
basic rules like the following; see also the next Q.
- Always read a newsgroup for a reasonable time before you post an
article to it.
- Pick the one right group for your article; don't crosspost unless
absolutely necessary. If you absolutely must post an article to
more than one group, do crosspost it and don't post the same
article separately to each group.
- Before you post a question, make sure you're posting to the right
newsgroup--the best way to do that is to observe the preceding
rule. Check the group's FAQ list (if it has one) to make sure
that your question isn't already answered there. See "Where are
FAQ lists archived?" in section C, "More information".
- When you post a question, if you ask for email responses then
promise to post a summary. Keep your promise. And make it a
real summary: don't just append all the email you got. Instead,
write your own (brief) description of the solution: this is the
best way to make sure you really understand it.
- Before you post a follow-up, read the other follow-ups. Very
often you'll find that someone else has already made the point you
had in mind.
- When someone posts a question, if you want to know the answer
don't post a "me, too". Instead send email to the poster asking
him or her to share responses with you.
- When posting a follow-up to another posted article, remove all
headers and signature lines from the old article; just keep the
line "In <article>, so-and-so writes:". Also cut the original
article down as much as possible; just keep enough of it to remind
readers of the context.
- Keep lines in posted articles to 72-75 characters. Many
newsreaders chop off column 81 or arbitrarily insert a newline
there, which makes longer lines difficult or impossible to read.
But you need to keep well below 80 characters per line to allow
for the > characters that get inserted when other people post
follow-ups to your article.
- Keep your signature to 4 lines or less (including any graphics),
and for heaven's sake make sure it doesn't get posted twice in
your article.
- Don't post email without first obtaining the permission of the
sender.
Subject: 107. How can I learn more about Usenet?
(new: 7 Aug 1993) There are two important newsgroups for learning
about how Usenet and newsreader software works:
- news.announce.newusers contains periodic postings that everybody
is asked to read before posting anything to Usenet. (In theory,
all new users are subscribed to news.announce.newusers
automatically. But in practice not all newsreader software does
that, so that many people violate the guidelines given there
simply because they don't know about them.)
- news.newusers.questions is described as "Q & A for users new to
the Usenet". But new and long-time users can ask or answer
questions about Usenet and newsreader software there. There's an
important article, "Welcome to news.newusers.questions! (weekly
posting)", that everyone is asked to read before posting to
news.newusers.questions. (See below for ways to get a copy of
that article.)
The following postings in news.announce.newusers might be considered
the "mandatory course" for new users:
Introduction to news.announce.newusers
What is Usenet?
Answers to Frequently Asked Questions
Rules for posting to Usenet
A Primer on How to Work With the Usenet Community
Hints on writing style for Usenet
Emily Postnews Answers Your Questions on Netiquette
The articles mentioned above are downloadable via ftp from
rtfm.mit.edu in the following files:
/pub/usenet/news.answers/news-newusers-intro
Welcome to news.newusers.questions! (weekly posting)
/pub/usenet/news.answers/news-announce-intro/part1
Introduction to news.announce.newusers
/pub/usenet/news.answers/what-is-usenet/part1
What is Usenet?
/pub/usenet/news.answers/usenet-faq/part1
Answers to Frequently Asked Questions
/pub/usenet/news.answers/posting-rules/part1
Rules for posting to Usenet
/pub/usenet/news.answers/usenet-primer/part1
A Primer on How to Work With the Usenet Community
/pub/usenet/news.answers/usenet-writing-style/part1
Hints on writing style for Usenet
/pub/usenet/news.answers/emily-postnews/part1
Emily Postnews Answers Your Questions on Netiquette
They are also available from the mail server whose address is
mail-server@rtfm.mit.edu. Send a message containing one or more
"send" command lines such as
send usenet/news.answers/news-newusers-intro
The "send" filenames are the same as the ftp filenames except the
"/pub" at the beginning is omitted. To get general information
about the mail server, send it a message containing "help".
Subject: 108. What other technical newsgroups should I know about?
(rev: 16 Aug 1993) Caution: Some of these newsgroups have
specialized charters; you'll probably get (and deserve) some flames
if you post to an inappropriate group. Most groups have FAQ lists
that will tell you what's appropriate. Don't post a request for the
FAQ list; instead, retrieve it yourself--see "Where are FAQ lists
archived?", in section C, "More information".
- misc.forsale.computers.d and misc.forsale.computers.pc-clone are
where you post notices of equipment, software, or computer books
that you want to sell. Please don't post or crosspost those
notices to comp.os.msdos.programmer.
- comp.os.ms-windows.programmer.tools and ...misc (formerly part of
comp.windows.ms.programmer): Similar to this group, but focus
on programming for the MS-Windows platform.
- comp.sys.ibm.pc.hardware is for more hardware-oriented discussions
of the machines that run DOS.
- the various comp.lang.* groups for articles and questions on the
programming languages. Caution: some groups welcome discussions
that are operating-system dependent or vendor specific; others do
not. For example, comp.lang.c is definitely _not_ for questions
about programming DOS or PC system features, even if the programs
are written in C. On the other hand, comp.lang.pascal contains
much discussion that is specific to Turbo Pascal.
- comp.binaries.ibm.pc.wanted: AFTER you have looked in the other
groups, this is the place to post a request for a particular
binary program.
- comp.archives.msdos.announce (moderated) explains how to use the
archive sites, especially Garbo and Simtel, and lists files
uploaded to them. Discussions belong in comp.archives.msdos.d,
which replaced comp.binaries.ibm.pc.archives in December 1992.
- MSDOS-Ann mailing list, for those who cannot subscribe to the
comp.archives.msdos.announce newsgroup, lists Simtel and Garbo
uploads in digest format. Instructions are downloadable as
/pc/MSDOSANN.ZIP from Garbo
pd1:<msdos.info>msdosann.zip from Simtel.
- comp.binaries.ibm.pc.d is for discussions about programs posted in
comp.binaries.ibm.pc, and only those programs. This is a good
place to report bugs in the programs, but not to ask where to find
them (see cbip.wanted, above). cbip.d is NOT supposed to be a
general PC discussion group.
- comp.sources.misc: a moderated group for source code for many
computer systems. It tends to get lots of Unix stuff, but you may
also pick up some DOS-compatible code here.
- alt.sources: an unmoderated group for source code. Guidelines are
posted periodically.
- Turbo Vision is a mailing list, not a newsgroup; send email to
listserv@vtvm1.cc.vt.edu if you want to subscribe.
section 2. Compile and link
===========================
Subject: 201. What the heck is "DGROUP > 64K"?
(rev: 18 Apr 1993) DGROUP is a link-time group of data segments, and
the compiler typically generates code that expects DS to be pointing
to DGROUP. (Exception: Borland's huge model has no DGROUP.)
Here's what goes into DGROUP:
- tiny model (all pointers near): DGROUP holds the entire program.
- small and medium models (data pointers near): DGROUP holds all
globals and static variables including string literals, plus the
stack and the heap.
- large, compact, and huge models in Microsoft (data pointers far):
DGROUP holds only initialized globals and static variables
including string literals, plus the stack and the near heap.
- large and compact models in Borland (data pointers far): DGROUP
holds initialized and uninitialized globals and static variables
including string literals, but not the stack or heap.
- huge model in Borland (data pointers far): there is no DGROUP, so
the 64K limit doesn't apply.
In all of the above, which is to say all six models in Microsoft C
and all but huge in Borland C, DGROUP is limited to 64K including
string literals (which are treated as static data). This limitation
is due to the Intel CPU's segmented architecture.
See the next Q for possible remedies.
For more information, see topics like "memory models" and "memory
management" in the index of your compiler manual. Also see
ti738.asc, downloadable as part of
pd1:<msdos.turbo-c>bchelp10.zip at Simtel
/pc/turbopas/bchelp10.zip at Garbo,
for an extended general discussion of memory usage in Borland C
programs, of which much applies to any C compiler in DOS.
Subject: 202. How do I fix "automatic data segment exceeds 64K" or
"stack plus data exceed 64K"?
These messages are a variation of "DGROUP > 64K". For causes,
please see the preceding Q.
If you get this error in tiny model, your program is simply too big
and you must use a different memory model. If you get this link
error in models S, C, M, L, or Microsoft's H, there are some things
you can do. (This error can't occur in Borland's huge model.)
If you have one or two big global arrays, simply declare them far.
The compiler takes this to mean that any references to them will use
32-bit pointers, so they'll be in separate segments and no longer
part of DGROUP.
Or you can use the /Gt[number] option with Microsoft or -Ff[=size]
with Borland C++ 2.0 and up. This will automatically put variables
above a certain size into their own segments outside of DGROUP.
Yet another option is to change global arrays to far pointers. Then
at the beginning of your program, allocate them from the far heap
(_fmalloc in Microsoft, farmalloc in Borland).
Finally, you can change to huge model (with Borland compilers, not
Microsoft). Borland's H model still uses far pointers by default,
but "sets aside the [64K] limit" and has no DGROUP group, according
to the BC++ 2.0 Programmer's Guide. Microsoft's H model does use
huge data pointers by default but retains DGROUP and its 64K limit,
so switching to the H model doesn't buy you anything if you have
DGROUP problems.
Subject: 203. Will Borland C code and Microsoft C code link together?
(rev: 15 Aug 1993) Typically this question is asked by someone who
owns compiler A and is trying to write code to link with a
third-party library that was compiled under compiler B.
The answer to the question is, Not in general. Here are some of the
reasons:
- "Helper" functions (undocumented functions for stack checking,
floating-point arithmetic, and operations on longs) differ between
the two compilers.
- The compilers may embed instructions in the object code that tell
the linker to look for their own run-time libraries. You can use
the linker option that says to ignore such instructions: /n in
TLINK, /NOD in the Microsoft linker (the one that comes with the C
compiler, not the one that used to come with DOS). But getting
around this problem will very likely just reveal other problems,
like different helper functions, that have no easy solution.
Those problems will generate link-time errors. Others may not show
up until run time:
- Borland's compact, large, and huge models don't assume DS=SS, but
Microsoft's do. The -Fs option on the Borland compiler, or one of
the /A options on Microsoft, should take care of this problem --
once you know that's what's going on.
- Check conventions for ordering and packing structure members, and
for alignment of various types on byte, word, paragraph, or other
boundaries. Again, you can generally adjust your code to match if
you know what conventions were used in compiling the "foreign"
libraries.
- Check the obvious and make sure that your code was compiled under
the same memory model as the code you're trying to link with.
(That's necessary, but no guarantee. Microsoft and Borland don't
use exactly the same conventions for segments and groups,
particularly in the larger memory models.)
That said, there are some circumstances where you can link hybrids.
Your best chance of success comes if you compile in large model with
the compiler switch that says to reload DS on entry to each
function, avoid longs and floating point, use only 16-bit pointers,
suppress stack checking, and specify all libraries used in the link.
Subject: 204. Why did my program bomb at run time with "floating point
formats not linked"?
First, is that the actual message, or did it say "floating point not
loaded"? If it was the latter, see the next Q.
You're probably using a Borland compiler for C or C++ (including
Turbo C and Turbo C++). Borland's compilers try to be smart and not
link in the floating-point (f-p) library unless you need it. Alas,
they all get the decision wrong. One common case is where you don't
call any f-p functions, but you have %f or other f-p formats in
scanf/printf calls. The cure is to call an f-p function, or at
least force one to be present in the link.
To do that, define this function somewhere in a source file but
don't call it:
static void forcefloat(float *p)
{ float f = *p; forcefloat(&f); }
It doesn't have to be in the module with the main program, as long
as it's in a module that will be included in the link.
If you have Borland C++ 3.0, the README file documents a slightly
less ugly work-around. Insert these statements in your program:
extern unsigned _floatconvert;
#pragma extref _floatconvert
Subject: 205. Why did my program bomb with "floating point not loaded"?
That is Microsoft C's run-time message when the code requires a
numeric coprocessor but your computer doesn't have one installed.
If the program is yours, relink it using the xLIBCE or xLIBCA
library (where x is the memory model).
Subject: 206. How can I change the stack size in Borland's C compilers?
In Turbo C, Turbo C++, and Borland C++, you may not find "stack
size" in the index but the global variable _stklen should be there.
The manual will instruct you to put a statement like
extern unsigned _stklen = 54321U;
in your code, outside of any function. You must assign the value
right in the extern statement; it won't work to assign a value at
run time. (The "extern" in this context isn't ANSI C and ought not
to be required, but the above statement is a direct quote from the
Library Reference manual of Borland C++ 2.0.) The linker may give
you a duplicate symbol warning, which you can ignore.
Subject: 207. What's the format of an .OBJ file?
(rev: 24 Sep 1993)
- base .OBJ format: Intel's document number #121748-001, {8086
Relocatable Object Module Formats}. (not verified)
Both Microsoft and Borland have extended the .OBJ format, as has IBM
for OS/2; and according to the MS-DOS encyclopedia, Microsoft
doesn't actually use all the listed formats.
- Microsoft-specific .OBJ formats:
* The .OBJ format document dated 14 Dec 1992, a WinHelp file from
the Microsoft developer's CD-ROM (266K after unzipping), is
downloadable as /vendor/microsoft/developer-network/ctech/11-9.zip
from ftp.uu.net. (verified by SB)
* A 45-page article can be found in the {MS-DOS Encyclopedia},
ISBN 1-55615-049-0 (verified by SB), now out of print.
* "Microsoft Object Module Format (OMF)" Specification, 22 Nov 1991,
was published by the Microsoft Languages Group. (not verified)
- Borland-specific .OBJ formats: Open Architecture Handbook. The
Borland Developer's Technical Guide, 1991, no ISBN. Chapter 2,
"Object file contents", (pages 27-50) covers the comment records
sent to the object file by Borland C++ version 3.0 and other
Borland compilers. The comment records mostly contain information
for the Borland debugger. (not verified)
- A "tutorial on the .OBJ format" comes with the VAL experimental
linker, downloadable as
pd1:<msdos.pgmutl>val-link.arc at Simtel
/pc/assembler/linker.zoo at Garbo.
Despite such different names, those files have the same contents,
but their contents are dated 18 Feb 1989. You'd be better off
with one of the more recent references listed above.
Subject: 208. What's the format of an .EXE header?
See pages 349-350 of {PC Magazine} 30 June 1992 (xi:12) for the old
and new formats. For a more detailed layout, look under INT 21
function 4B in Ralf Brown's interrupt list. Ralf Brown's list
includes extensions for Borland's TLINK and Borland debugger info.
Among the books that detail formats of executable files are {DOS
Programmer's Reference: 2d Edition} by Terry Dettman and Jim Kyle,
ISBN 0-88022-458-4; and {Microsoft MS-DOS Programmer's Reference},
ISBN 1-55615-329-5.
Subject: 209. What's the difference between .COM and .EXE formats?
To oversimplify: a .COM file is a direct image of core, and an .EXE
file will undergo some further relocation when it is run (and so it
begins with a relocation header). A .COM file is limited to 64K for
all segments combined, but an .EXE file can have as many segments as
your linker will handle and be as large as RAM can take.
The actual file extension doesn't matter. DOS knows that a file
being loaded is in .EXE format if its first two bytes are MZ or ZM;
otherwise it is assumed to be in .COM format. For instance, DR-DOS
6.0's COMMAND.COM is in .EXE format.
section 3. Keyboard
===================
Subject: 301. How can I read a character without echoing it to the
screen, and without waiting for the user to press the
Enter key?
The C compilers from Microsoft and Borland offer getch (or getche to
echo the character); Turbo Pascal has ReadKey.
In other programming languages, load 8 in register AH and execute
INT 21; AL is returned with the character from standard input
(possibly redirected). If you don't want to allow redirection, or
you want to capture Ctrl-C and other special keys, use INT 16 with
AH=10; this will return the scan code in AH and ASCII code (if
possible) in AL, except that AL=E0 with AH nonzero indicates one of
the grey "extended" keys was pressed. (If your BIOS doesn't
support the extended keyboard, use INT 16 function 0 not 10.)
Subject: 302. How can I find out whether a character has been typed,
without waiting for one?
In Turbo Pascal, use KeyPressed. Both Microsoft C and Turbo C offer
the kbhit( ) function. All of these tell you whether a key has been
pressed. If no key has been pressed, they return that information
to your program. If a keystroke is waiting, they tell your program
that but leave the key in the input buffer.
You can use the BIOS call, INT 16 function 01 or 11, to check
whether an actual keystroke is waiting; or the DOS call, INT 21
function 0B, to check for a keystroke from stdin (subject to
redirection). See Ralf Brown's interrupt list.
Subject: 303. How can I disable Ctrl-C/Ctrl-Break and/or Ctrl-Alt-Del?
(rev: 11 Sep 1993) Several utilities are downloadable from
pd1:<msdos.keyboard> at Simtel. In that directory, cadel.zip
contains a TSR (with source code) to disable those keys. Also,
keykill.arc contains two utilities: keykill.com lets you disable up
to three keys of your choice, and deboot.com changes the boot key to
leftShift-Alt-Del.
C programmers who simply want to make sure that the user can't
Ctrl-Break out of their program can use the ANSI-standard signal( )
function; the Borland compilers also offer ctrlbrk( ) for handling
Ctrl-Break. However, if your program uses normal DOS input such as
getch( ), ^C will appear on the screen when the user presses Ctrl-C
or Ctrl-Break. You can avoid the ^C echo for Ctrl-C by using
_bios_keybrd( ) in MSC or bioskey( ) in BC++; however, Ctrl-Break
will still terminate the program.
An alternative approach involves programming input at a lower level.
You can use INT 21 function 7, which allows redirection but doesn't
echo the ^C (or any other character, for that matter); or use INT 16
function 0 or 10; or hook INT 9 to discard Ctrl-C and Ctrl-Break
before the regular BIOS keyboard handler sees them; etc., etc.
You should be aware that Ctrl-C and Ctrl-Break are processed quite
differently internally. Ctrl-Break, like all keystrokes, is
processed by the BIOS code at INT 9 as soon as the user presses the
keys, even if earlier keys are still in the keyboard buffer: by
default the handler at INT 1B is called. Ctrl-C is not special to
the BIOS, nor is it special to DOS functions 6 and 7; it _is_
special to DOS functions 1 and 8 when at the head of the keyboard
buffer. You will need to make sure BREAK is OFF to prevent DOS
polling the keyboard for Ctrl-C during non-keyboard operations.
Some good general references are {Advanced MS-DOS} by Ray Duncan,
ISBN 1-55615-157-8; {8088 Assembler Language Programming: The IBM
PC}, ISBN 0-672-22024-5, by Willen & Krantz; and {COMPUTE!'s Mapping
the IBM PC}, ISBN 0-942386-92-2.
Subject: 304. How can I disable the print screen function?
There are really two print screen functions: 1) print current
screen snapshot, triggered by PrintScreen or Shift-PrtSc or
Shift-grey*, and 2) turn on continuous screen echo, started and
stopped by Ctrl-P or Ctrl-PrtSc.
1) Screen snapshot to printer
The BIOS uses INT 5 for this. Fortunately, you don't need to mess
with that interrupt handler. The standard handler, in BIOSes dated
December 1982 or later, uses a byte at 0040:0100 (alias 0000:0500)
to determine whether a print screen is currently in progress. If it
is, pressing PrintScreen again is ignored. So to disable the screen
snapshot, all you have to do is write a 1 to that byte. When the
user presses PrintScreen, the BIOS will think that a print screen is
already in progress and will ignore the user's keypress. You can
re-enable PrintScreen by zeroing the same byte.
Here's some simple code:
void prtsc_allow(int allow) /* 0=disable, nonzero=enable */ {
unsigned char far* flag = (unsigned char far*)0x00400100UL;
*flag = (unsigned char)!allow;
}
2) Continuous echo of screen to printer
If ANSI.SYS is loaded, you can easily disable the continuous echo of
screen to printer (Ctrl-P or Ctrl-PrtSc). Just redefine the keys by
"printing" strings like these to the screen (BASIC print, C printf,
Pascal Write statements, or ECHO command in batch files):
<27>[0;114;"Ctrl-PrtSc disabled"p
<27>[16;"^P"p
Change <27> in the above to an Escape character, ASCII 27.
If you haven't installed ANSI.SYS, I (SB) can't offer an easy way to
disable the echo-screen-to-printer function. Please send any tested
solutions to the editor.
Actually, you might not need to disable Ctrl-P and Ctrl-PrtSc. If
your only concern is not locking up your machine, when you see the
"Abort, Retry, Ignore, Fail" prompt just press Ctrl-P again and then
I. As an alternative, install one of the many print spoolers that
intercept printer-status queries and always return "Printer ready".
Subject: 305. How can my program turn NumLock (CapsLock, ScrollLock)
on or off?
First, if you just don't want NumLock turned on when you reboot,
check your system's setups. (Use Ctrl-Alt-Enter any time, or press
a special key like Del at boot time, or run the setup program
supplied with your system.) Many systems now have an option in
setup to turn NumLock off at boot time.
You need to twiddle bit 5, 6, or 4 of location 0040:0017. Here's
some code: lck( ) turns on a lock state, and unlck( ) turns it off.
(The status lights on some keyboards may not reflect the change. If
yours is one, call INT 16 function 2, "get shift status", and that
may update them. It will certainly do no harm.)
#define NUM_LOCK (1 << 5)
#define CAPS_LOCK (1 << 6)
#define SCRL_LOCK (1 << 4)
void lck(int shiftype) {
char far* kbdstatus = (char far*)0x00400017UL;
*kbdstatus |= (char)shiftype;
}
void unlck(int shiftype) {
char far* kbdstatus = (char far*)0x00400017UL;
*kbdstatus &= ~(char)shiftype;
}
Subject: 306. How can I speed up the keyboard's auto-repeat?
The keyboard speed has two components: delay (before a key that you
hold down starts repeating) and typematic rate (the speed once the
key starts repeating). Most BIOSes since 1986 let software change
the delay and typematic rate by calling INT 16 function 3, "set
typematic rate and delay"; see Ralf Brown's interrupt list. If you
have DOS 4.0 or later, you can use the MODE CON command that you'll
find in your DOS manual.
On 83-key keyboards (mostly XTs), the delay and typematic rate can't
easily be changed. According to the {PC Magazine} of 15 Jan 1991,
page 409, to adjust the typematic rate you need "a memory-resident
program which simply '[watches]' the keyboard to see if you're
holding down a key ... and after a certain time [starts] stuffing
extra copies of the held-down key into the buffer." No source code
is given in that issue; but the QUICKEYS utility that {PC} published
in 1986 does this sort of watching (not verified); source and object
code are downloadable in pd1:<msdos.pcmag>vol5n05.arc from Simtel.
Subject: 307. What is the SysRq key for?
There is no standard use for the key. The BIOS keyboard routines in
INT 16 simply ignore it; therefore so do the DOS input routines in
INT 21 as well as the keyboard routines in libraries supplied with
high-level languages.
When you press or release a key, the keyboard triggers hardware line
IRQ1, and the CPU calls INT 9. INT 9 reads the scan code from the
keyboard and the shift states from the BIOS data area.
What happens next depends on whether your PC's BIOS supports an
enhanced keyboard (101 or 102 keys). If so, INT 9 calls INT 15
function 4F to translate the scan code. If the translated scan code
is 54 hex (for the SysRq key) then INT 9 calls INT 15 function 85
and doesn't put the keystroke into the keyboard buffer. The default
handler of that function does nothing and simply returns. (If your
PC has an older BIOS that doesn't support the extended keyboards,
INT 15 function 4F is not called. Early ATs have 84-key keyboards,
so their BIOS calls INT 15 function 85 but nor 4F.)
Thus your program is free to use SysRq for its own purposes, but at
the cost of some programming. You could hook INT 9, but it's
probably easier to hook INT 15 function 85, which is called when
SysRq is pressed or released.
Subject: 308. How can my program tell what kind of keyboard is on the
system?
Ralf Brown's Interrupt List includes MEMORY.LST, a detailed
breakdown by Robin Walker of the contents of the BIOS system block
that starts at 0040:0000. Bit 4 of byte 0040:0096 is "1=enhanced
keyboard installed". C code to test the keyboard type:
char far *kbd_stat_byte3 = (char far *)0x00400096UL;
if (0x10 & *kbd_stat_byte3)
/* 101- or 102-key keyboard is installed */
{PC Magazine} 15 Jan 1991 issue suggests on page 412 that "for some
clones [the above test] is not foolproof". If you use this method
in your program you should provide the user some way to override
this test, or at least some way to tell your program to assume a
non-enhanced keyboard. The article suggests a different approach to
determining the type of keyboard.
Subject: 309. How can I tell if input, output, or stderr has been
redirected?
(rev: 24 Sep 1993) Normally, input and output are associated with
the console (i.e., with the keyboard and the screen, respectively).
If either is not, you know that it has been redirected. Some source
code to check this is available at the usual archive sites.
If you program in Turbo Pascal, you'll want this downloadable
collection of Turbo Pascal units:
/pc/ts/tspa33*.zip at Garbo
pd1:<msdos.turbopas>tspa33*.zip at Simtel.
(where the * is 70, 60, 55, 50, or 40 for Turbo Pascal 7.0, 6.0,
5.5, 5.0, or 4.0 respectively.) Source code is not included. Also
see the downloadable Frequently Asked Questions files by Timo Salmi:
/pc/ts/tsfaqp15.zip at Garbo
pd1:<msdos.info>tsfaqp15.zip at Simtel.
If you program in C, use isatty( ) if your implementation has it.
Otherwise, pd1:<msdos.sysutl>is_con10.zip is downloadable from
Simtel; it includes source code.
Good references for the principles are {PC Magazine} 16 Apr 1991
(x:7) pg 374; Ray Duncan's {Advanced MS-DOS}, ISBN 1-55615-157-8, or
Ralf Brown's interrupt list for INT 21 function 4400; and Terry
Dettman and Jim Kyle's {DOS Programmer's Reference: 2d edition},
ISBN 0-88022-458-4, pp 602-603.
Subject: 310. How can I increase the size of the keyboard buffer?
(new: 20 June 1993) SB tested only one of the many available device
drivers that do this, namely BUF160, which extends the keyboard
buffer to 160 characters. It performed flawlessly for two years
with MS-DOS 5 and Windows 3.1. It's downloadable as
pd1:<msdos.keyboard>buf160_6.zip at Simtel
/pc/keyboard/buf160_6.zip at Garbo.
Subject: 311. How can I stuff characters into the keyboard buffer?
(new: 15 Aug 1993) If your computer has an enhanced keyboard (see
"How can my program tell what kind of keyboard is on the system?",
above), then put the scan code in CH, the ASCII character in CL, 5
in AH, and execute INT 16. The return in AL is 0 for success or 1
for buffer full.
(continued in part 3)