Book Image

Tcl/Tk 8.5 Programming Cookbook

Book Image

Tcl/Tk 8.5 Programming Cookbook

Overview of this book

With Tcl/Tk, you can create full-featured cross-platform applications in a simple and easy-to-understand way without any expensive development package; the only tools required are a simple text editor and your imagination. This practical cookbook will help you to efficiently interact with editors, debuggers, and shell type interactive programs using Tcl/Tk 8. This cookbook will comprehensively guide you through practical implementation of Tcl/Tk 8.5 commands and tools. This book will take you through all the steps needed to become a productive programmer in Tcl/Tk 8. Right from guiding you through the basics to creating a stand-alone application, it provides complete explanation of all the steps along with handy tips and tricks. The book begins with an introduction to the Tcl shell, syntax, variables, and programming best practices in the language. It then explores procedures and the flow of events with control constructs followed by advanced error trapping and recovery. From Chapter 4, a detailed study of string expressions and handling enables you to handle various string functions and use lists to expand the string functionality. The book then discusses in-depth the Tcl Dictionary and how to utilize it to store and retrieve data. File operations and Tk GUI handling are covered extensively along with a developing a real-world address book application to practice the concepts learned.
Table of Contents (20 chapters)
Tcl/Tk 8.5 Programming Cookbook
About the Author
About the Reviewers

Returning a range of characters from a string

It is not uncommon to cut a string into its constituent parts. This allows the data to be stored in-line, without comma or space separation, thereby, minimizing the impact on the disk storage. To assist us in this, and other instances where we need to extract a range of characters from a string, Tcl has provided the range keyword.

The syntax of the string command is as follows:

string range string first last

When invoked with the range keyword, the string command will return all characters inclusive between those specified in the first and last location.

How to do it…

In the following example we will locate a range of characters contained within a string. Return values from the commands are provided for clarity. Enter the following command:

% string range abcdefg 2 4

How it works…

As you can see, Tcl has returned the characters "cde", based on the index values passed. The string command returns a range of consecutive characters from the string...