Q: I want to have a printed documentation of my students' Turbo
Pascal program exercises. How is all input and output directed 
also
to the printer?

 A1: Use a screen 
capturing program to put everything that comes
onto the screen into a file, and print the file. See FAQPROGS.TXT 
in
ftp://garbo.uwasa.fi/pc/ts/tsfaqn43.zip (or whatever version number
is the current) for more about these programs. Available by
anonymous FTP or mail server from garbo.uwasa.fi.

 A2: See the code in 
TSPAS.NWS (item: Redirecting writes to the
printer) in the ftp://garbo.uwasa.fi/pc/ts/tspa3470.zip (or whatever
is the current version number) Turbo Pascal units package (70 = 
40,
50, 55, 60, or 70 depending on your TP version). Alternatively use
USECON and USEPRN routines in the TSUNTG unit of the same 
package.

     
+------------------------------------------+
     ! To get these and other packages given as !
     !   /dir/subdir/name                       !
     ! see the instructions in PD2ANS.TXT       !
     +------------------------------------------+

 A3: But the really 
elegant solution to the problem of getting a
logfile (or a printed list) of a Turbo Pascal run is to rewrite the
write(ln) and read(ln) device driver functions. In itself writing
such driver redirections is very advanced Turbo Pascal 
programming,
but when the programming has once been done, the system is 
extremely
easy to use as many times as you like. It goes like this. The driver
redirections are programmed into a unit (say, tpulog or tpuprn). All
that is needed after that is to include the following uses statement
into the program (the target program) which has to be logged:
      uses TPULOG;    ( or )    uses TPUPRN;
This is all there is to it. Just adding one simple line to the
target program. (If you call any other units, "uses 
tpulog" must
come AFTER the system units (e.g. Dos), but BEFORE any which 
you may
define yourself!)
   The reason that I have named two units here instead of just one
in the above example is that the preferred log for the target
program may be a logfile or the printer. The better solution of
these two is to use the logfile option, and then print it. The
reason is simple. If the target program itself prints something,
your printout will look confused.
   The logging also has obvious limitations. It works for standard
input and output (read(ln) and write(ln)) only. 1) It does not
support graphics, in other words it is for the textmode. 2) It does
not support direct (Crt) screen writes. 3) And, naturally it only
shows the input and output that comes to the screen. Not any other
input or output, such as from or to a file. 4) Furthermore, you are
not allowed to reassign input or output. Statements like assign
(output, '') will result in a crash, because the rewritten output
device redirections are invalidated by such statements. 5) The
device on the default drive must not be write protected, since else
the logfile cannot be written to it. 6) It does not work for Turbo
Pascal 4.0. Despite these restrictions, the method is perfectly
suited for logging students' Turbo Pascal escapades.
   It is advisable first to test and run your target program without
"tpulog", so that if you get any strange errors you'll 
know whether
they are caused by the logging.
   Where to get such a unit. The code can be found in Michael
Tischer (1990), Turbo Pascal Internals, Abacus, Section 4.2. Next 
a
few of my own tips on this unit Tischer calls Prot. 1) The code is
in incorrect order. The code that is listed on pages 142 - 145 goes
between pages 139 and 140. 2) You can change the logfile name 
(const
prot_name) to lpt1 for a printed list of the target program run. In
that case it is advisable to include a test for the online status of
the printer within Tischer's unit. 3) I see no reason why the two
lines in Tischer's interface section couldn't be transferred to the
implementation section. Why have any global definitions?  But all 
in
all, it works like magic!

 A4: From: 
abcscnuk@csunb.csun.edu (Naoto Kimura (ACM))
Subject: Re: Printing a log of students' exercises revisited
To: ts@uwasa.fi
Date: Fri, 2 Nov 90 20:52:03 pdt
[Reproduced with Naoto's kind permission]
By the way, several months ago, I had submitted a file (nktools.zip)
file on SimTel that contains sources to a unit (LOGGER), which
allows logging of I/O going through the standard input and output
files, while still being able to use the program interactively.  I
believe that I also submitted a copy to your site.  It was something
I put together for use by students here at California State
University at Northridge.  The source works equally well in all
presently available versions of Turbo Pascal.
The only requirements are that
 * you place it as one of the last entries in the USES clause.  If
   there is anything that redirects the standard input and output
   file variables, you should put that unit before my unit in the
   USES clause, so that it can see the I/O stream.
 * Don't use the GotoXY and similar screen display control
   procedures in the Crt unit and expect it to come out the same way
   you had it on the display.  Since all my unit does is just
   capture the I/O stream to send it through the normal channels and
   also to the log file, all screen control information is not sent
   to the log file.
 * All I/O you want logged should go through the standard input and
   output file variables.
 * Don't close the standard input and output file variables, because
   it will cause problems.  Basically, as far as I have checked, it
   just causes the logging to stop at that point.