Tcl/Tk - Procedures and Variable Scope

Procedures and Variable Scope - Tcl/Tk module T207

As your code grows from 1 to 10 to 100 lines, you'll find that it's helpful to split it into a series of logical blocks, each of which can be run as a command. You'll learn how to define such procedures, how to pass information in and out of them, and how to access information that's held in your main program and in the calling procedure too.

This topic is presented on public course Tcl Basics

Examples from our training material

add2	Answer to final exercise
addindemo	Sample code to complete - final exercise
cbn	Using upvar to call by name
doublit	Another upvar example for learners
gsc	The global scope
p1	Sharing a variable using global
p2	Sharing a variable using upvar
p3	Sharing a variable using upvar and call by name - RECOMMENED
p4	returning a variable - RECOMMENED for passing 1 piece of data back
p5	Sharing a variable using uplevel - obscure
pr1	Defining a proc (command) and using it
pr3	loading a file of procs shared with other applications
scope1	Variable default to being local
up1	using upvar to effect a variable in the calling code
uquery	Shared file of procs
uv	Call by value and call by name
vardemo	Calling a proc with a variable number of arguments
whatandwhen	Exercise - please write the proc to complete
wwanswer	First sample answer - "getnumber"
wwbetter	Better sample answer - "getnumber"

Opentalk forum discussions related to this topic

Passing arrays in and out of procedures
Using variables defined inside the procedure
Pulling a list out of a proceedure
Procedure with variable number of arguments
Passing lists into procedures

Pictures

Radia software is tailored through Tcl procedures
Teaching Tcl around the world

Background information

Some modules are available for download as a sample of our material or under an Open Training Notes License for free download from http://www.training-notes.co.uk.

Topics covered in this module

Holding commonly used command sequences.
Why use procs?.
Sharing procedures with another application.
Variable parameters.
Variable scope.
The global scope.
The upvar command.
Another example of upvar.
Structured programming and OO.
Structured programming.
Programming with objects.
Use of Procs as an interface to Tcl.

Complete learning

If you are looking for a complete course and not just a information on a single subject, visit our Listing and schedule page.

Well House Consultants specialise in training courses in Tcl/Tk, Expect,Python, Perl, PHP, and MySQL. We run Private Courses throughout the UK (and beyond for longer courses), and Public Courses at our training centre in Melksham, Wiltshire, England. It's surprisingly cost effective to come on our public courses - even if you live in a different country or continent to us.

We have a technical library of over 600 books on the subjects on which we teach. These books are available for reference at our training centre. Also available is the Opentalk Forum for discussion of technical questions.