Errata for 4th Edition

Practical Programming in Tcl and Tk
ISBN: 0-13-038560-3

This page reflects errors that were found in the 4th edition of the book. If you found an error that is not listed here, please send me a note at with the word "book" in the subject and mention that you did not see it here.

Special thanks to the readers noted in italics that reported these errors.

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Last update Mon Aug 18 20:21:30 PDT 2014


pli3rd bullet point in the Why Tcl? section should say "available on the Internet" instead of "available on the network".
Sean Mitchell
plx4th Edition Thanks section, 2nd paragraph. Third word from end of paragraph should be "and" not "an".
Gary Roth

Chapter 3

p37Example 3-3 botches the first line of output. It should be
puts "Content-Type: text/html"
Marty Leisner
p42The first paragraph should say "loop variable name" instead of "loop variable x"
Pierre-Marie Le Biot

Chapter 4

p50The string first description should say that -1 is returned if subString is not found (not string)
p52The text next to the Hot Tip may be confusing. Kevin suggests this, which reads pretty well:
"Despite the quotes, the expression operators that work on numbers and strings first try converting items to numbers if possible, and then the operators convert them back if they detect a case of string comparison."
I would add that it helps to know that Tcl represents values internally as both a string and some other native value, like a double-precision floating point, or 32-bit integer, or Tcl list, or byte code, or binary blob. Tcl Math expressions compute values that are native double-precision values, and are only converted to strings for printing. The Hot Tip is reminding us that there are some automatic conversions between native representations and strings, and in some subtle cases those conversions might suprise you. Tcl_Obj values are described in Chapter 47 on C programming.
Kevin Jennings
p55The caption for Example 4-4 says "Microsoft World" instead of "Microsoft Word".
Marcin Siebert
p57Near the bottom of the page, the format %#08x should result in:
because the field width of 8 includes the leading 0x.
Hemang Lavana

Chapter 5

p65Example 5-1. The last line of the example has an extra }. It should be:
 => {{1 2} {a b} {$foo}} {1 2}
Simon Klempert

Chapter 6

p78There is a reference to regular expressions and Chapter 11 with a stray "page" in it. The closest page reference would be to page 145, Regular Expression Syntax.
Steve Munnings
p84Example 6-15. The paragraph after this example says that the catch command is not grouped with curly braces, but it is. (It wasn't in earlier editions.) It turns out you can get away without the curly braces, as in:
if [catch { blah } result ] { # handle error }
But it is better style and slightly more efficient to always enclose the if expression in braces.
Simon Klempert

Chapter 7

p89The cross reference for namespaces should be Chapter 14, not Chapter 7.
Simon Klempert

Chapter 8

p99The second-to-last line says "Example 5-8 uses on array", which should be "Example 5-8 uses one array."
Yang Wang
p100In the last paragraph, the word implement should be implemented
Damien Lynch
p102The first paragraph says "Example 8-10 defines RecordInsert" but it should say it defines RecordAppend.
Yang Wang

Chapter 9

p109Table 9-2. The file volumes command does not take a name argument.
Marty Leisner
p123Example 9-11. The second foreach erroneously has curly braces around its [glob -nocomplain *] list value argument.
Alex Brown

Chapter 10

p133Example 10-2 has a typo in the rename command, which should be
  rename $procName $procName-orig
p136In the middle of the page, after
PackedButton .save "Save" { Save $file } {-side left}
The next two in-line examples should reference .save instead of .new. E.g., they should be:
button .save -text Save -command { Save $file }
pack .save -side left

Yang Wang

Chapter 11

p150In the last paragraph, the in-line reference to the pattern [[:<:]] is missing a right bracket.
Mike Schincariol
p162In Table 11-7 the pattern for hexadecimal numbers is incorrect. It includes the character ranges a-hA-H, which of course should be a-fA-F. This same bug also appears on p164.
Andrew Ching

Chapter 12

p174In the first paragraph of the Packages Implemented in C Code section, there is an incorrect reference to Chapter 37. It should refer to Chapter 47.
Damien Lynch

Chapter 13

p191In the paragraph before Example 13-6, the last sentence is missing an "and":
Chapter 10 describes callbacks and why the curly braces are used with eval as they are in this example:
Steve Munnings

Chapter 14

p211-212 The in-line examples for namespace code return a new command that begins with ::namespace inscope. The book omits the leading ::, which is present to ensure the command is not ambiguous. If you evaluated that command in a namespace that (foolishly) had its own namespace command, you would not want to use that redefined namespace command.
Marty Leisner

Chapter 15

p221 In Conversions Between Encodings, the gb12345 encoding is incorrectly referred to as the Big5 encoding. Those are in fact two different encodings. See
Andrew Tannenbaum

Chapter 17

p240 In Example 17-1 it is safer to cancel the after event when the socket becomes writeable, otherwise it could be possible for the after event to run after the fileevent and incorrectly change the value of the connected variable.
set ::afterid [after $timeout {set connected timeout}]
set sock [socket -async $host $port]
fileevent $sock w {after cancel $::afterid ; set connected ok}
vwait connected
Zoran Slavulj

Chapter 18

p265 In Example 18-5 the call to Mtype_Add has its arguments reversed. It should read:
Mtype_Add .junk application/myjunk
Ricardo Jorge
p275 In Example 18-16 the two uses of html::varEmpty should really be ncgi::empty
Hank Liu
p276 In Example 18-17 there is an extra double-quote (") after addr2 in the arguments to Form_Simple
Ricardo Jorge
p278 In Table 18-2 the procedure name Url_PrefixInstall is misspelled.
Andy Goth

Chapter 22

p355 Example 22-5 is missing the $ in the second reference to $starkit::topdir
Rainer Schwarzinger
p355 Example 22-6 doesn't create the "data" file. One way to do that would be
echo "Hello, World!" > write.vfs/data
Rainer Schwarzinger

Chapter 24

p378Example 24-1 does not work as written on Windows because of limitations in pipes on that platform. Here is a version that works on Windows by using the cmd command processor. Note, however, that output is still batched up and so the fileevent is not really necessary.
Ben Ginsberg
p385The CD-ROM version of Example 24-3 has an out of date cross reference to the Scrolled_Text procedure in a comment. The cross reference in the printed example is correct.
Marty Leisner
p393The screen shots in examples 24-5, 24-6, 24-7 are not updated, so they incorrectly refer to Example 31-3, which is now really Example 37-3.
Marty Leisner

Chapter 25

p401The second sentence in the first paragraph should read:
"Due to other constraints the request might not be honored, ..."
Mike Beaufort

Chapter 26

p412-414The screen shots in this chapter were taken on Windows where wish has a white default background. If you are on a Unix platform you will need to preface the examples with
. config -bg white

Marty Leisner
p415Example 26-7 could usefully cross reference the numeric color specifications shown on page 622.
Marty Leisner
p416Example 26-9 is supposed to be tried interactively so you can see the effect of each of the three grid commands. If you run the whole example you'll end up with the appearance in the lower right figure. In addition, the text of the labels should be "left side" and "right side".
Marty Leisner
p418Example 26-11 is missing from the CD-ROM archive.
Marty Leisner

Chapter 33

p500The CD-ROM version of Example 33-1 loads the "/etc/passwd" file, while the printed example loads the sample Tk file "colors.tcl".
Marty Leisner
p502The CD-ROM version of Example 33-3 It is missing the three toplevel commands at the end of the example.
Marty Leisner

Chapter 34

p509Table 34-1 does not list %S, which is "The text string being inserted/deleted, if any, {} otherwise."
Marty Leisner
p510The paragraph before Example 34-3 should say "Example 34-3 demonstrates..."
Marty Leisner

Chapter 37

p558At the top of the page, the tk scale command should be tk scaling
Andrew Tannenbaum

Chapter 39

p604The bindings for Tab and Shift-Tab are not correct because tk_focusNext and tk_focusPrev don't actually set the focus (they did in an early Tk 4.0 beta...). The current bindings are now:
bind all <Tab> {tkTabToWindow [tk_focusNext %W]}
bind all <Shift-Tab> {tkTabToWindow [tk_focusPrev %W]}
Andrew Tannenbaum
p606Using both Example 39-1 and 39-2 together reveals an inconsistency in the value of the variable used to wait. In 39-1 it is set to "cancel", but in 39-2 it expect it to be either "0" or "1". The simplest fix is to change Dialog_Wait in Example 39-1 to contain:
bind $top  [list set $varName 0]
Andreas Brodmann

Chapter 44

p660In the first paragraph under the Icons section, the state operation returns iconic, not "iconified"
Ron Hart

Chapter 41

p632On Windows, the no cursor should result in no cursor being displayed. However, due to a bug in Tk 8.3 and 8.4, the cursor is a circle with a slash through it.
Roy Terry

Chapter 46

p689Example 46-7: The Bind_Save procedure takes args but is never passed anything. Instead, it should use the global bind(class) value.
  proc Bind_Save { dotfile } {
    global bind
    set out [open $ w]
    foreach w $bind(class) {
      # etc
Greg Edwards

Chapter 47

p701In Example 47-2, the sprintf call specifies buf as its first argument. That should be buffer.
Art Morel

Chapter 49

p765In Example 49-15 the ClockEventProc should cancel the timer event associated with the TICKING flag in the case where it schedules the ClockDisplay. This avoids queuing up lots and lots of extra calls to the Display procedure.
    if ((clockPtr->tkwin != NULL) &&
            !(clockPtr->flags & REDRAW_PENDING)) {

        if (clockPtr->flags & TICKING) {
            clockPtr->flags &= ~TICKING;

        Tk_DoWhenIdle(ClockDisplay, (ClientData) clockPtr);
        clockPtr->flags |= REDRAW_PENDING;
Dave Wolff


p837There are no entries for < or > under Symbols. These are used as event delimiters on page 439.
Andrew Tannenbaum
p843The clock command is missing from the index, nor is it listed as a sub-entry under the Tcl Command index entry. However, clock is listed in the command index on page 22, and is described starting on page 183.
p838Entry for "arrow on canvas" should reference page 572.
p849Entry for "file: is plain" is really about "file: isfile. This confusion shows up for the "plain file" cross reference, which should really be a "see also" reference.
p856Entry for "lsearch, Tcl command" should reference page 69.