Discuss Tcl-Tk ”; Previous Next Tcl is a general purpose multi-paradigm system programming language. It is a scripting language that aims at providing the ability for applications to communicate with each other. On the other hand, Tk is a cross platform widget toolkit used for building GUI in many languages. This tutorial covers various topics ranging from the basics of the Tcl/Tk to its scope in various applications. Print Page Previous Next Advertisements ”;
Tcl-Tk – Useful Resources ”; Previous Next The following resources contain additional information on Tcl-Tk. Please use them to get more in-depth knowledge on this topic. Useful Links on Tcl-Tk Official Site – Official Site for Tcl-Tk Details about Tcl-Tk − Wikipedia Reference for Tcl-Tk More Details – Know more details about Tcl-Tk Useful Books on Tcl-Tk To enlist your site on this page, please drop an email to [email protected] Print Page Previous Next Advertisements ”;
Tk – Events ”; Previous Next Events in its simplest form is handled with the help of commands. A simple example for event handling is event handling with button and is shown below − #!/usr/bin/wish proc myEvent { } { puts “Event triggered” } pack [button .myButton1 -text “Button 1” -command myEvent] When we run the above program, we will get the following output − A simple program to show delay text animation event is shown below − #!/usr/bin/wish proc delay {} { for {set j 0} {$j < 100000} {incr j} {} } label .myLabel -text “Hello…………….” -width 25 pack .myLabel set str “Hello…………….” for {set i [string length $str]} {$i > -2} {set i [expr $i-1]} { .myLabel configure -text [string range $str 0 $i] update delay } When we run the program, we will get the following output in animated way − Event after delay The syntax for event after delay is shown below − after milliseconds number command A simple program to show after delay event is shown below − #!/usr/bin/wish proc addText {} { label .myLabel -text “Hello…………….” -width 25 pack .myLabel } after 1000 addText When we run the program, we will get the following output after one second − You can cancel an event using the after cancel command as shown below − #!/usr/bin/wish proc addText {} { label .myLabel -text “Hello…………….” -width 25 pack .myLabel } after 1000 addText after cancel addText Event Binding The syntax for event binding is as shown below − bind arguments Keyboard Events Example #!/usr/bin/wish bind . {puts “Key Pressed: %K “} When we run the program and press a letter X, we will get the following output − Key Pressed: X Mouse Events Example #!/usr/bin/wish bind . {puts “Button %b Pressed : %x %y “} When we run the program and press the left mouse button, we will get an output similar to the following − Button 1 Pressed : 89 90 Linking Events with Button Example #!/usr/bin/wish proc myEvent { } { puts “Event triggered” } pack [button .myButton1 -text “Button 1” -command myEvent] bind . “.myButton1 invoke” When we run the program and press enter, we will get the following output − Event triggered Print Page Previous Next Advertisements ”;
Tk – Overview ”; Previous Next Tk refers to Toolkit and it provides cross platform GUI widgets, which helps you in building a Graphical User Interface. It was developed as an extension to Tcl scripting language by John Ousterhout. Tk remained in development independently from Tcl with version being different to each other, before, it was made in sync with Tcl in v8.0. Features of Tk It is cross platform with support for Linux, Mac OS, Unix, and Microsoft Windows operating systems. It is an open source. It provides high level of extendibility. It is customizable. It is configurable. It provides a large number of widgets. It can be used with other dynamic languages and not just Tcl. GUI looks identical across platforms. Applications Built in Tk Large successful applications have been built in Tcl/Tk. Dashboard Soft User Interface Forms GUI for Relational DB Ad Hoc GUI for Relational DB Software/Hardware System Design Xtask – Task Management Musicology with Tcl and Tk Calender app Tk mail Tk Debugger Print Page Previous Next Advertisements ”;
Tk – Images ”; Previous Next The image widget is used to create and manipulate images. The syntax for creating image is as follows − image create type name options In the above syntax type is photo or bitmap and name is the image identifier. Options The options available for image create are listed below in the following table − Sr.No. Syntax & Description 1 -file fileName The name of the image file name. 2 -height number Used to set height for widget. 3 -width number Sets the width for widget. 4 -data string Image in base 64 encoded string. A simple example for image widget is shown below − #!/usr/bin/wish image create photo imgobj -file “/Users/rajkumar/Desktop/F Drive/pictur/vb/Forests/ 680049.png” -width 400 -height 400 pack [label .myLabel] .myLabel configure -image imgobj When we run the above program, we will get the following output − The available function for image are listed below in the following table − Sr.No. Syntax & Description 1 image delete imageName Deletes the image from memory and related widgets visually. 2 image height imageName Returns the height for image. 3 image width imageName Returns the width for image. 4 image type imageName Returns the type for image. 5 image names Returns the list of images live in memory. A simple example for using the above image widget commands is shown below − #!/usr/bin/wish image create photo imgobj -file “/Users/rajkumar/images/680049.png” -width 400 -height 400 pack [label .myLabel] .myLabel configure -image imgobj puts [image height imgobj] puts [image width imgobj] puts [image type imgobj] puts [image names] image delete imgobj The image will be deleted visually and from memory once “image delete imgobj” command executes. In console, the output will be like the following − 400 400 photo imgobj ::tk::icons::information ::tk::icons::error ::tk::icons:: warning ::tk::icons::question Print Page Previous Next Advertisements ”;
Tk – Geometry Manager ”; Previous Next The geometry manager is used to manage the geometry of the window and other frames. We can use it to handle the position and size of the window and frames. The layout widgets are used for this purpose. Positioning and sizing The syntax for positioning and sizing window is shown below − wm geometry . wxh+/-x+/-y Here, w refers to width and h refers to height. It is followed by a ”+” or ”-” sign with number next referring to the x position on screen. Similarly the following ”+” or ”-” sign with number refers to the y position on screen A simple example is shown below for the above Statement −. #!/usr/bin/wish wm geometry . 300×200+100+100 When we run the above program, we will get the following output − Grid Geometry The syntax for grid geometry is shown below − grid gridName -column number -row number -columnspan number -rowspan number The column, row, columnspan, or rowspan helps in providing the grid geometry. A simple example is shown below for the above statement − #!/usr/bin/wish frame .myFrame1 -background red -height 100 -width 100 frame .myFrame2 -background blue -height 100 -width 50 grid .myFrame1 -columnspan 10 -rowspan 10 -sticky w grid .myFrame2 -column 10 -row 2 When we run the above program, we will get the following output − Print Page Previous Next Advertisements ”;
Tcl – Error Handling ”; Previous Next Error handling in Tcl is provided with the help of error and catch commands. The syntax for each of these commands is shown below. Error syntax error message info code In the above error command syntax, message is the error message, info is set in the global variable errorInfo and code is set in the global variable errorCode. Catch Syntax catch script resultVarName In the above catch command syntax, script is the code to be executed, resultVarName is variable that holds the error or the result. The catch command returns 0 if there is no error, and 1 if there is an error. An example for simple error handling is shown below − Live Demo #!/usr/bin/tclsh proc Div {a b} { if {$b == 0} { error “Error generated by error” “Info String for error” 401 } else { return [expr $a/$b] } } if {[catch {puts “Result = [Div 10 0]”} errmsg]} { puts “ErrorMsg: $errmsg” puts “ErrorCode: $errorCode” puts “ErrorInfo:n$errorInfon” } if {[catch {puts “Result = [Div 10 2]”} errmsg]} { puts “ErrorMsg: $errmsg” puts “ErrorCode: $errorCode” puts “ErrorInfo:n$errorInfon” } When the above code is executed, it produces the following result − ErrorMsg: Error generated by error ErrorCode: 401 ErrorInfo: Info String for error (procedure “Div” line 1) invoked from within “Div 10 0” Result = 5 As you can see in the above example, we can create our own custom error messages. Similarly, it is possible to catch the error generated by Tcl. An example is shown below − Live Demo #!/usr/bin/tclsh catch {set file [open myNonexistingfile.txt]} result puts “ErrorMsg: $result” puts “ErrorCode: $errorCode” puts “ErrorInfo:n$errorInfon” When the above code is executed, it produces the following result − ErrorMsg: couldn”t open “myNonexistingfile.txt”: no such file or directory ErrorCode: POSIX ENOENT {no such file or directory} ErrorInfo: couldn”t open “myNonexistingfile.txt”: no such file or directory while executing “open myNonexistingfile.txt” Print Page Previous Next Advertisements ”;
Tcl – File I/O ”; Previous Next Tcl supports file handling with the help of the built in commands open, read, puts, gets, and close. A file represents a sequence of bytes, does not matter if it is a text file or binary file. Opening Files Tcl uses the open command to open files in Tcl. The syntax for opening a file is as follows − open fileName accessMode Here, filename is string literal, which you will use to name your file and accessMode can have one of the following values − Sr.No. Mode & Description 1 r Opens an existing text file for reading purpose and the file must exist. This is the default mode used when no accessMode is specified. 2 w Opens a text file for writing, if it does not exist, then a new file is created else existing file is truncated. 3 a Opens a text file for writing in appending mode and file must exist. Here, your program will start appending content in the existing file content. 4 r+ Opens a text file for reading and writing both. File must exist already. 5 w+ Opens a text file for reading and writing both. It first truncate the file to zero length if it exists otherwise create the file if it does not exist. 6 a+ Opens a text file for reading and writing both. It creates the file if it does not exist. The reading will start from the beginning, but writing can only be appended. Closing a File To close a file, use the close command. The syntax for close is as follows − close fileName Any file that has been opened by a program must be closed when the program finishes using that file. In most cases, the files need not be closed explicitly; they are closed automatically when File objects are terminated automatically. Writing a File Puts command is used to write to an open file. puts $filename “text to write” A simple example for writing to a file is shown below. #!/usr/bin/tclsh set fp [open “input.txt” w+] puts $fp “test” close $fp When the above code is compiled and executed, it creates a new file input.txt in the directory that it has been started under (in the program”s working directory). Reading a File Following is the simple command to read from a file − set file_data [read $fp] A complete example of read and write is shown below − Live Demo #!/usr/bin/tclsh set fp [open “input.txt” w+] puts $fp “test” close $fp set fp [open “input.txt” r] set file_data [read $fp] puts $file_data close $fp When the above code is compiled and executed, it reads the file created in previous section and produces the following result − test Here is another example for reading file till end of file line by line − Live Demo #!/usr/bin/tclsh set fp [open “input.txt” w+] puts $fp “testntest” close $fp set fp [open “input.txt” r] while { [gets $fp data] >= 0 } { puts $data } close $fp When the above code is compiled and executed, it reads the file created in previous section and produces the following result − test test Print Page Previous Next Advertisements ”;
Tcl – Lists ”; Previous Next List is one of the basic data-type available in Tcl. It is used for representing an ordered collection of items. It can include different types of items in the same list. Further, a list can contain another list. An important thing that needs to be noted is that these lists are represented as strings completely and processed to form individual items when required. So, avoid large lists and in such cases; use array. Creating a List The general syntax for list is given below − set listName { item1 item2 item3 .. itemn } # or set listName [list item1 item2 item3] # or set listName [split “items separated by a character” split_character] Some examples are given below − Live Demo #!/usr/bin/tclsh set colorList1 {red green blue} set colorList2 [list red green blue] set colorList3 [split “red_green_blue” _] puts $colorList1 puts $colorList2 puts $colorList3 When the above code is executed, it produces the following result − red green blue red green blue red green blue Appending Item to a List The syntax for appending item to a list is given below − append listName split_character value # or lappend listName value Some examples are given below − Live Demo #!/usr/bin/tclsh set var orange append var ” ” “blue” lappend var “red” lappend var “green” puts $var When the above code is executed, it produces the following result − orange blue red green Length of List The syntax for length of list is given below − llength listName Example for length of list is given below − Live Demo #!/usr/bin/tclsh set var {orange blue red green} puts [llength $var] When the above code is executed, it produces the following result − 4 List Item at Index The syntax for selecting list item at specific index is given below − lindex listname index Example for list item at index is given below − Live Demo #!/usr/bin/tclsh set var {orange blue red green} puts [lindex $var 1] When the above code is executed, it produces the following result − blue Insert Item at Index The syntax for inserting list items at specific index is given below. linsert listname index value1 value2..valuen Example for inserting list item at specific index is given below. Live Demo #!/usr/bin/tclsh set var {orange blue red green} set var [linsert $var 3 black white] puts $var When the above code is executed, it produces the following result − orange blue red black white green Replace Items at Indices The syntax for replacing list items at specific indices is given below − lreplace listname firstindex lastindex value1 value2..valuen Example for replacing list items at specific indices is given below. Live Demo #!/usr/bin/tclsh set var {orange blue red green} set var [lreplace $var 2 3 black white] puts $var When the above code is executed, it produces the following result − orange blue black white Set Item at Index The syntax for setting list item at specific index is given below − lset listname index value Example for setting list item at specific index is given below − Live Demo #!/usr/bin/tclsh set var {orange blue red green} lset var 0 black puts $var When the above code is executed, it produces the following result − black blue red green Transform List to Variables The syntax for copying values to variables is given below − lassign listname variable1 variable2.. variablen Example for transforming list into variables is given below − Live Demo #!/usr/bin/tclsh set var {orange blue red green} lassign $var colour1 colour2 puts $colour1 puts $colour2 When the above code is executed, it produces the following result − orange blue Sorting a List The syntax for sorting a list is given below − lsort listname An example for sorting a list is given below − Live Demo #!/usr/bin/tclsh set var {orange blue red green} set var [lsort $var] puts $var When the above code is executed, it produces the following result − blue green orange red Print Page Previous Next Advertisements ”;
Tcl – Loops ”; Previous Next There may be a situation, where you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on. Programming languages provide various control structures that allow for more complicated execution paths. A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages − Tcl language provides the following types of loops to handle looping requirements. Sr.No. Loop Type & Description 1 while loop Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body. 2 for loop Executes a sequence of statements multiple times and abbreviates the code that manages the loop variable. 3 nested loops You can use one or more loop inside any another while, for or do..while loop. Loop Control Statements Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed. Tcl supports the following control statements. Sr.No. Control Statement & Description 1 break statement Terminates the loop or switch statement and transfers execution to the statement immediately following the loop or switch. 2 continue statement Causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating. The Infinite Loop A loop becomes infinite loop if a condition never becomes false. The while loop is traditionally used for this purpose. You can make an endless loop by leaving the conditional expression as 1. while {1} { puts “This loop will run forever.” } When the conditional expression is absent, it is assumed to be true. Tcl programmers more commonly use the while {1} construct to signify an infinite loop. NOTE − You can terminate an infinite loop by pressing Ctrl + C keys. Print Page Previous Next Advertisements ”;