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Everything is a string - even a list

Almost all variables in Tcl are held as strings ... if you use integers and stirings in calculations such as expr and incr. the strings are converted back and forth intergally. Lists, too, are held as strings of characters in which chunks of string are counted / taken out as being elements in the list. Here's an example setting up a list ... and then reporting the length as a list (where it contains two values), and as a string (where it contains 15 letters).

  % set daze "Monday Chewsday"
  Monday Chewsday
  % puts daze
  daze
  % puts $daze
  Monday Chewsday
  % put [string length $daze]
  15
  % put [llength $daze]
  2
  %


Note my use of almost - Tcl's arrays are NOT held as simple strings - and that does make a difference (later in Tcl course we'll take a look at this)
(written 2015-03-11)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
T205 - Tcl/Tk - String Handling in Tcl
  [4455] Working out distance between places, using OS grid references and a program in Tcl - (2015-03-11)
  [4205] Regular Expression Substitution - Tcl - (2013-11-12)
  [3576] Tcl - apparently odd behaviour of string trimleft - (2012-01-13)
  [3285] Extracting data from a string / line from file - Tcl - (2011-05-10)
  [3192] Tcl - Some example of HOW TO in handling data files and formats - (2011-03-04)
  [2472] split and join in tcl and expect - (2009-10-23)
  [1601] Replacing the last comma with an and - (2008-04-04)
  [1410] Tcl / regsub - changing a string and using interesting bits - (2007-10-27)
  [1403] Square Bracket protection in Tcl - (2007-10-23)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [779] The fragility of pancakes - and better structures - (2006-06-26)
  [404] How to check that a string contains a number in Tcl - (2005-08-06)

T206 - Tcl/Tk - Lists
  [4209] Lists in Tcl - fundamentals in a commented source code example - (2013-11-16)
  [3618] lists and struct::list in Tcl - Introduction to struct::list and examples - (2012-02-18)
  [3583] Expanding a list of parameters in Tcl - {*} and eval - (2012-01-17)
  [3582] Tcl collections - lists, dicts and array - (2012-01-16)
  [3415] User defined sorting and other uses of callbacks in Tcl and Tk - (2011-09-02)
  [3394] The difference between lists and strings - Tcl - (2011-08-16)
  [2468] What are Tcl lists? - (2009-10-22)
  [1405] Sorting in Tcl - lists and arrays - (2007-10-24)
  [1402] Tcl - append v lappend v concat - (2007-10-23)
  [1334] Stable sorting - Tcl, Perl and others - (2007-09-06)
  [1283] Generating traffic for network testing - (2007-07-29)
  [1282] Stringing together Tcl scripts - (2007-07-29)
  [781] Tcl - lappend v concat - (2006-06-27)
  [463] Splitting the difference - (2005-10-13)
  [144] Tcl sandwich - lists in Tcl - (2004-12-08)


Back to
Tcl variable names - no real limits!
Previous and next
or
Horse's mouth home
Forward to
Working out distance between places, using OS grid references and a program in Tcl
Some other Articles
A new Tcl/tk example - a window to show system status
Test framework for TCL - Tcltest - some examples
Objects in Tcl - iTcl - updated first steps example
Everything is a string - even a list
Tcl variable names - no real limits!
Binary data handling - Python and Perl
Running an operating system command from your Python program - the new way with the subprocess module
Deciding whether to use parameters, conditional statements or subclasses
Spike solution, refactoring into encapsulated object methods - good design practise
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