Aihuxp.110
NET.blfp
utzoo!decvax!ucbvax!mhtsa!ihnss!ihuxp!shqer
Tue Jul 28 13:40:23 1981
BLFP 3.22
From: ihn5g!jdd
Subject: BLFP 3.22
(This newsletter may contain proprietary information so it is not to
be distributed outside Bell Labs.)
Bell Labs Free Press Tuesday, 28 July 1981 Volume 3 : Issue 22
Today's Topics:
HP2621p Printer Malfuntion, Forgotten Command: diff3,
Printing Strings in Debuggers
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>From karn Mon Jul 27 17:41:16 1981 CDT remote from ihnss
Subject: hp printer falling behind
One possibility is the XON/XOFF handshake option in the terminal.
Check the "x" handshake option and make sure it is set.
Phil
------------------------------
>From ber Tue Jul 28 01:27:37 1981 remote from harpo
Subject: hp2621p
It sounds to me like your terminal is not running the Xon/Xoff protocol
check the straps. Mine are:
handshake
---------
etX
which is what UNIX likes to see. Let me know if this does it.
brian
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>From ikeya!rob Tue Jul 28 01:48 EDT 1981 remote from research
Subject: HP2621's and the lot
The HP2621 has a buffer to store received characters, and the printer
goes at less than 1200 baud, so if the characters are coming at 1200
baud or faster, the terminal cannot keep up. The X "strap" may be set,
which causes the terminal to spew ^S/^Q to control the buffer filling up.
However, the amount of space left in the buffer when the ^S is sent
is small, although larger in more recent terminals, and some Unices
do not stop sending before the buffer fills up. It takes code in
the driver to handle 2621's properly.
If the buffer fills up or the terminal receiver gets overruns, the
terminal puts delete characters in the buffer.
------------------------------
>From rsk Sun Jul 26 20:33:01 1981 remote from pur-ee
Subject: Forgotten Commands
I got one for ya...."diff3" which does a three-way file
comparison--sure beats running "diff" three times and slogging through
all the output...
By the way, I was surprised to hear that "pack" and "unpack" are
not in common use at your site--since disk-limits are tight and rigidly
enforced here, everybody, and i mean everybody, uses "pack" to save space.
pur-ee!rsk
rich kulawiec
[pur-ee no longer receives the BLFP because they are non-BTL. JLS]
------------------------------
>From steffen Tue Jul 28 12:28:10 1981 CDT remote from ihuxp
Subject: Portability Problem: Printing Strings in Debuggers
Although C does not have a string data type per se, character arrays
are commonly used as a defacto string data type. A fixed size char
array is used to contain a variable length string of chars
terminated by a null char.
The problem is how to safely print char arrays as strings in
debugging tools. If you tell printf to print a char array as
a string it prints chars until it finds a null char (value of 0), so
if the char array does not contain a null char, and it does not find
one before it reaches the end of the allowed address spectrum, the
program aborts due to a bus or memory error.
Obviously you must limit the number of characters printed, but how
do you determine the limit? The compiler symbol
table contains the length of all the char arrays, but this does not
tell you the length of an array passed as an arguement to a
function. Picking an arbitrary limit (like 50) does not work
because some char arrays may be longer, and you will still get a
memory error if you try to print a char array that is smaller than
the limit and abuts the address boundry. Thus, the debugger must
really know the allowable address range for the program so it can
make sure that it does not exceed it when printing a char array.
Is there a portable method of determining this address range? I say
"portable" because there is a subroutine flow tracing program
("trace" in the Unix Stockroom) which has solved this problem for
PDP 11 Unix, but the solution does not appear to be portable. I
would prefer something that would be portable across all
implementations of the C language, but since this may be impossible,
I will settle for portability across all versions of Unix. The
a.out file should contain the address range information, but is it
the same for all versions of Unix?
Joe Steffen
ihuxp!steffen or ihuxk!steffen
IH 2C-331 x5381
------------------------------
End of Bell Labs Free Press
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