- Tcl/Tk 8.5 Programming Cookbook
- Copyright
- Credits
- About the Author
- Acknowledgment
- About the Reviewers
- www.PacktPub.com
- Preface
- 1. The Tcl Shell
- 2. Using the Building Blocks Control Constructs
- 3. Error Handling
- 4. Handling String Expressions
- Introduction
- Appending to a string
- Formatting a string
- Matching a regular expression within a string
- Performing character substitution on a string
- Parsing a string using conversion specifiers
- Determining the length of a string
- Comparing strings
- Comparing a string of characters
- Locating the first instance of a character
- Locating the index of a character
- Determining the class of a string
- Locating the last instance of a string
- Determining the size of a string
- Replacing values within a string
- Locating a pattern within a string
- Returning a range of characters from a string
- Creating a string of repeated characters
- Replacing ranges of characters contained within a string
- Creating a reverse string
- Converting a string to lowercase
- Converting a string to title
- Converting a string to uppercase
- Trimming a string
- Trimming leading whitespace
- Trimming trailing whitespace
- Locating the word end
- Locating the word start
- Performing variable substitution
- 5. Expanding String Functionality Using Lists
- Introduction
- Creating a list
- Joining two lists
- Joining list elements
- Appending list elements
- Assigning list elements to variables
- Retrieving an element from a list
- Inserting elements into a list
- Determining the number of elements
- Getting a list element
- Repeating elements
- Replacing elements
- Reversing elements
- Searching a list
- Editing a list
- Sorting a list
- Splitting a string into a list
- 6. The Tcl Dictionary
- Introduction
- Creating a dictionary
- Appending to a dictionary
- Determining if a key exists
- Filtering a dictionary
- Searching a dictionary
- Getting a record
- Incrementing a value
- Getting the dictionary structure
- Getting a list of keys
- Appending to an existing record
- Merging two dictionaries
- Creating a blank dictionary structure
- Updating variables from a dictionary
- Determining the size of a dictionary
- Getting all records
- Assigning values
- 7. File Operations
- 8. Tk GUI Programming with Tcl/Tk
- 9. Configuring and Controlling Tk Widgets
- 10. Geometry Management
- 11. Using Tcl Built-in Dialog Windows
- 12. Creating and Managing Menus
- 13. Creating the Address Book Application
Now that we have a named dictionary with key/value pairs, it becomes necessary to determine if the given key exists. To accomplish this, Tcl provides the dict exists command. The syntax is as follows:
dict exists DictionaryValue key… key…
In the following example, we will create a dictionary containing a set of key/value pairs and then determine whether or not a specific key exists. Return values from the commands are provided for clarity. Enter the following command:
% set names [dict create 1 John 2 Mary 3 Paul]
1 John 2 Mary 3 Paul
% dict exists $names 3
1
The dict exists command returns a Boolean value to indicate if the specified key exists in the dictionary referenced in name. A return value of 1 indicates that the key exists, while a return of 0 indicates that it does not. Be aware that this command will return an error if dictionaryValue does not reference an existing dictionary.
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