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TCL and OTCL programming

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• OTcl
  • Tcl and OTcl

    TCL is pronounced "Tickle" TCL is a scripting programming language - similar to PERL or Python (Scripting languages are usually interpreted and have dynamic typing Very good for quick and dirty jobs) Object TCL (OTCL) is an object oriented extension of TCL OTcl is written in C++ OTCL's library of objects can be extended by adding object definitions in the C++ source code

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  • NS2 and OTcl

    The NS2 network simulator consists mainly of object extensions written in C++ that have been added to OTcl Built-in objects include: Node (is a router) Links (output buffers) TCP Agents (simulate all kinds of TCP protocols) ... Simulator object A special simulator object is defined in NS2 that perform process-based simulation on the network objects To write a network simulation program in NS2, the programmer simply write an OTcl program that creates network objects and one (special) simulator object

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  • Presentation order:

    We will learn to program in TCL and Then we will look at OTcl very briefly how to create objects how to invoke methods in objects Lastly, learn how to use the Network objects defined in NS2           (they are OTcl objects !!!)

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  • External resources to learn TCL:
    • Univ. of Chicago: click here

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• Variables
  • Defining variable:

    You do not need to define a variable before you use it When a new name is encountered, TCL will assume that it is a new variable

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  • Name of a variable:

    Variable names in Tcl can contain any characters and be of any length. To get exotic characters (like whitespace) into a variable name you may need to quote it (i.e., use {....}); Using exotic names (with characters other than letters, digits and _  ) are generally a bad idea.

    More on variable names when we learn to use variables below....

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• Variable Type
  • All variable are auto-typed and dynamically typed

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  • Auto-typing:

    Auto-typing means that type of the variable depends on the value stored in the variable

  • Dynamic typing:

    Dynamically typed means that type of the variable can change over time... (this can be confusing at times)

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• TCL statements
  • A TCL statement always consists of:

    A command name Optionally followed by one or more arguments (parameters) - unlike conventional programming language, the parameters are not given between brackets !

    Example:

    set x "Hello World"

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  • Number of parameters:

    Most Tcl command has a fixed number of arguments There are a few Tcl command (such as expr ) that has a variable number of arguments If you specify an incorrect number of arguments to a command, you will receive an error and the Tcl program will terminate.

   

   

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  Assignment Command/Statement

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• Assignent Statement: set command
  • The set command is used to assign values to variables

  • The set command has 2 forms , depending on the number of arguments given:

    set varName value # Assign value to variable varName set varName # Return value in variable varName

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  • Examples:

    set b 1234 // Associate b with 1234 set b // return 1234 (value associated with b)

  • Note:

    When using "set b", an error occurs if there is no variable named "b".

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• Obtaining the content of a variable
  • You can obtain the value of a variable using the set command:

    set x Hello // assigned Hello to x set x // Obtain the value of variable x

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  • There is a more common way to obtain the value of a variable:

    By using Tcl's substitution operator "$" Syntax: $variableName will replace "variableName" with the content of that variable

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    Examples:

    set b 56 // Asscoiate b with 56 puts b // Output: b puts [set b] // Output: 56 puts $b // Output: 56

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• Variable names revisited
  • Unlike most conventional programming languages, you can use any character in a variable name.... but...

  • However, you would be wise to stick to using only the following set of characters:

    letters digits underscore

    That is because the substitution operator ($) assumes that variables names consists only of these characters.

  • Fact:

    If a variables name contains characters with special meaning (e.g., "-" means subtract) then you need to use braces {...} to "quote" the name of the variable - This practice is a pretty ugly business....

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  • Examples:

    set foo-bar 1234 // Associate foo-bar with 1234 puts $foo-bar // Error // Error message: "foo": no such variable // (- character interpreted as minus operation) puts ${foo-bar} // Output: 1234

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• The unset command
  • The unset command deletes the named variables and all storage associated with them.

  • After an unset, any attempt to refer to the value of those variables results in an error.

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• Querying information: info
  • The info command can be used to obtain information on various things

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• Check for the existance of a variable: The info exists command

  • The info exists varName command returns:

    1 if the variable varName exists          0 if it does not exist

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• List all variables: The info vars command
  • The info vars command returns a list of all defined variables (in the current scope).

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• Arrays
  • Just like simple variables, you don't have to define array variables before using them.

  • Array variable syntax:

    variableName ( index )

    Example:

    set A(2) 4567 # A(2) = 4567 puts $A(2) # Print content of A(2)

  • An array variable is created when you first assign a value to it.

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• Find out the size of an array: The array size command
  • The array size command returns number of elements in the array

  • Note:

    Arrays are dynamic, and the array size can change !

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  • Example:

    set A(2) 4567 # A(2) = 4567 puts [array size A] # Output: 1 set A(6) 1111 # A(6) = 1111 puts [array size A] # Output: 2

  • Note:

    Each array element has an independent from other array elements; not like Java.

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  • In Java, when you define an array:

    int A[] = new int[10];

    You define the array elements A[0], A[1], A[2], A[3], A[4], A[5], A[6], A[7], A[8], A[9]

    In fact, if A[2] exist, we know that A[0] and A[1] must also exist !

  • In TCL, when you create array element A(2):

    set A(2) 4567 # A(2) = 4567

    Only element A(2) is created and nothing else.

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• The associative array
  • The TCL's array is in fact an associative array

  • Arrays in procedural languages (such as Java, C, C++, can only be indexed by integers

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  • Associative arrays:

    Associateive arrays are arrays than are indexed by strings Associative arrays are also called dictionaries

  • Examples:

    set A(cs455) Cheung # A(cs355) = Cheung set A( cs455 ) Cheung # Error: No spaces allowed in array name !!! puts $A(cs455) # prints Cheung set s cs455 # s = cs455 puts $A($s) # prints Cheung !!!

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  • The reason that associative arrays are called dictionaries is the fact that you can make a dictionary with it:

    set dict[red] "Color, associated with fire" set dict[dead] "Opposite of alive"

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• Unsetting an array
  • You can unset individual array element:

    Example:

    unset A(smith) # unsets A(smith) unset A(jones) # unsets A(jones)

  • You can unset an entire array (all elements):

    Example:

    unset A # unsets all elements of A

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• Multi-dimensional arrays
  • Tcl does not have multidimensional arrays...

    but associative arrays can simulate them easily:

    set A(1,1) 0 set A(1,2) 0 set A(1,3) 0 set A(2,1) 0 set A(2,2) 0 set A(2,3) 0

  • NOTE:
    • The array names for the example above will return:

      2,2 1,3 2,3 1,1 2,1 1,2

    So there is no need for nested loops to process multidimensional arrays in TCL