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PHP with MySQL Essential Training
Illustration by Don Barnett

Constants


From:

PHP with MySQL Essential Training

with Kevin Skoglund

Video: Constants

We started off this chapter by talking about variables. So, it's fitting that we're going to end it by talking about constants. As you can guess from the name, a constant is the opposite of a varible. A vaible can change or vary. A constant can't change. It remains constantly set at the same value. Constants are going to be recognizable on PHP because they're always written in all capital letters and there's no dollar sign in front of them. They're also going to differ from variables in another way. The only way to set a value for constant is to use a function. The define function. You can't just use the equal sign to assign a value. Like you can with variable.
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  1. 4m 8s
    1. Welcome
      1m 0s
    2. Using the exercise files
      3m 8s
  2. 15m 6s
    1. What is PHP?
      3m 52s
    2. The history of PHP
      2m 51s
    3. Why choose PHP?
      4m 10s
    4. Installation overview
      4m 13s
  3. 54m 53s
    1. Overview
      2m 33s
    2. Working with Apache Web Server
      6m 56s
    3. Changing the document root
      7m 24s
    4. Enabling PHP
      6m 16s
    5. Upgrading PHP
      3m 30s
    6. Configuring PHP
      10m 3s
    7. Installing MySQL
      5m 46s
    8. Configuring MySQL
      7m 24s
    9. Text editor
      5m 1s
  4. 31m 25s
    1. Overview
      3m 27s
    2. Installing WampServer
      5m 46s
    3. Finding the document root
      2m 24s
    4. Configuring PHP
      8m 12s
    5. Configuring MySQL
      5m 45s
    6. Text editor
      5m 51s
  5. 19m 12s
    1. Embedding PHP code on a page
      6m 43s
    2. Outputting dynamic text
      5m 55s
    3. The operational trail
      2m 27s
    4. Inserting code comments
      4m 7s
  6. 1h 18m
    1. Variables
      7m 50s
    2. Strings
      4m 38s
    3. String functions
      8m 54s
    4. Numbers part one: Integers
      6m 27s
    5. Numbers part two: Floating points
      5m 25s
    6. Arrays
      10m 0s
    7. Associative arrays
      6m 37s
    8. Array functions
      6m 33s
    9. Booleans
      3m 50s
    10. NULL and empty
      5m 15s
    11. Type juggling and casting
      8m 27s
    12. Constants
      4m 43s
  7. 27m 37s
    1. If statements
      6m 0s
    2. Else and elseif statements
      4m 16s
    3. Logical operators
      7m 30s
    4. Switch statements
      9m 51s
  8. 42m 15s
    1. While loops
      8m 41s
    2. For loops
      5m 59s
    3. Foreach loops
      8m 16s
    4. Continue
      8m 28s
    5. Break
      4m 8s
    6. Understanding array pointers
      6m 43s
  9. 37m 25s
    1. Defining functions
      8m 25s
    2. Function arguments
      5m 32s
    3. Returning values from a function
      7m 33s
    4. Multiple return values
      4m 53s
    5. Scope and global variables
      6m 2s
    6. Setting default argument values
      5m 0s
  10. 20m 18s
    1. Common problems
      3m 47s
    2. Warnings and errors
      8m 36s
    3. Debugging and troubleshooting
      7m 55s
  11. 57m 57s
    1. Links and URLs
      5m 33s
    2. Using GET values
      5m 35s
    3. Encoding GET values
      8m 41s
    4. Encoding for HTML
      9m 26s
    5. Including and requiring files
      7m 40s
    6. Modifying headers
      6m 45s
    7. Page redirection
      6m 43s
    8. Output buffering
      7m 34s
  12. 1h 3m
    1. Building forms
      7m 28s
    2. Detecting form submissions
      5m 59s
    3. Single-page form processing
      7m 57s
    4. Validating form values
      10m 40s
    5. Problems with validation logic
      9m 54s
    6. Displaying validation errors
      7m 23s
    7. Custom validation functions
      6m 28s
    8. Single-page form with validations
      7m 25s
  13. 28m 5s
    1. Working with cookies
      2m 49s
    2. Setting cookie values
      5m 55s
    3. Reading cookie values
      6m 1s
    4. Unsetting cookie values
      4m 51s
    5. Working with sessions
      8m 29s
  14. 48m 39s
    1. MySQL introduction
      6m 43s
    2. Creating a database
      7m 41s
    3. Creating a database table
      7m 42s
    4. CRUD in MySQL
      5m 48s
    5. Populating a MySQL database
      7m 32s
    6. Relational database tables
      6m 40s
    7. Populating the relational table
      6m 33s
  15. 56m 4s
    1. Database APIs in PHP
      4m 51s
    2. Connecting to MySQL with PHP
      7m 45s
    3. Retrieving data from MySQL
      8m 47s
    4. Working with retrieved data
      6m 12s
    5. Creating records with PHP
      6m 58s
    6. Updating and deleting records with PHP
      9m 6s
    7. SQL injection
      3m 5s
    8. Escaping strings for MySQL
      6m 45s
    9. Introducing prepared statements
      2m 35s
  16. 35m 58s
    1. Blueprinting the application
      7m 19s
    2. Building the CMS database
      5m 14s
    3. Establishing your work area
      4m 38s
    4. Creating and styling the first page
      4m 22s
    5. Making page assets reusable
      6m 36s
    6. Connecting the application to the database
      7m 49s
  17. 32m 49s
    1. Adding pages to the navigation subjects
      5m 58s
    2. Refactoring the navigation
      6m 7s
    3. Selecting pages from the navigation
      6m 2s
    4. Highlighting the current page
      5m 26s
    5. Moving the navigation to a function
      9m 16s
  18. 1h 45m
    1. Finding a subject in the database
      9m 48s
    2. Refactoring the page selection
      10m 52s
    3. Creating a new subject form
      6m 55s
    4. Processing form values and adding subjects
      11m 20s
    5. Passing data in the session
      9m 16s
    6. Validating form values
      9m 40s
    7. Creating an edit subject form
      8m 30s
    8. Using single-page submission
      7m 44s
    9. Deleting a subject
      9m 44s
    10. Cleaning up
      10m 37s
    11. Assignment: Pages CRUD
      4m 30s
    12. Assignment results: Pages CRUD
      6m 10s
  19. 39m 26s
    1. The public appearance
      8m 52s
    2. Using a context for conditional code
      11m 37s
    3. Adding a default subject behavior
      6m 9s
    4. The public content area
      5m 51s
    5. Protecting page visibility
      6m 57s
  20. 1h 3m
    1. User authentication overview
      4m 3s
    2. Admin CRUD
      8m 41s
    3. Encrypting passwords
      7m 26s
    4. Salting passwords
      5m 42s
    5. Adding password encryption to CMS
      11m 54s
    6. New PHP password functions
      3m 13s
    7. Creating a login system
      11m 28s
    8. Checking for authorization
      5m 48s
    9. Creating a logout page
      5m 40s
  21. 2m 4s
    1. Next steps
      2m 4s

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PHP with MySQL Essential Training
14h 24m Beginner Jun 04, 2013

Viewers: in countries Watching now:

PHP is a popular, reliable programming language at the foundation of many smart, data-driven websites. This comprehensive course from Kevin Skoglund helps developers learn the basics of PHP (including variables, logical expressions, loops, and functions), understand how to connect PHP to a MySQL database, and gain experience developing a complete web application with site navigation, form validation, and a password-protected admin area. Kevin also covers the basic CRUD routines for updating a database, debugging techniques, and usable user interfaces. Along the way, he provides practical advice, offers examples of best practices, and demonstrates refactoring techniques to improve existing code.

Topics include:
  • What is PHP?
  • Installing and configuring PHP and MySQL
  • Exploring data types
  • Controlling code with logical expressions and loops
  • Using PHP's built-in functions
  • Writing custom functions
  • Building dynamic webpages
  • Working with forms and form data
  • Using cookies and sessions to store data
  • Connecting to MySQL with PHP
  • Creating and editing database records
  • Building a content management system
  • Adding user authentication
Subjects:
Developer Servers Programming Languages Web Development
Software:
MySQL PHP
Author:
Kevin Skoglund

Constants

We started off this chapter by talking about variables. So, it's fitting that we're going to end it by talking about constants. As you can guess from the name, a constant is the opposite of a varible. A vaible can change or vary. A constant can't change. It remains constantly set at the same value. Constants are going to be recognizable on PHP because they're always written in all capital letters and there's no dollar sign in front of them. They're also going to differ from variables in another way. The only way to set a value for constant is to use a function. The define function. You can't just use the equal sign to assign a value. Like you can with variable.

Lets try some experiments. want to open up basic.html. And then we'll just do save as. And we're going to call this constants.php. Change the title here to constants. And let's give ourselves a PHP block. Now, we know how variables work. Let's say we had max width equals to 980. That would be a variable set at the integer 980. But if was a constant max width would not have the dollar sign in front of it and it would be in all capital letters. So it would be MAX_WIDTH, and if we wanted to set MAX_WIDTH to 980 we can't to it by just simply saying 980.

That doesn't work with Constant. Because we're going to be doing them only rarely we need to use this special function to do it. We're going to use define, and then we're going to provide the name of the constant. In quotes, max width. The second argument then will be the value that we want to set it to, and that's going to define max width for us, now notice that we used the quotes here, but most of the time when we talk about the constant we don't use the quotes. Why don't we use them here? Well if you think about it... This is a constant.

But how can we use a constant if it hasn't been defined yet, right? So we have to use quotes until it's been defined. We're just providing PHP with the string that we'd like to use for the name of it, so don't let that trip you up. Now, once it's been defined, then of course We can echo back the value and see that it's been set. Let's just do that real quick. I'll save that and we'll switch back over to Firefox. And instead of typecasting, we're looking for constants. So there it is, 980. That's the value that's being echoed back as max width.

Now, we can't change the value. Let's just see that real quick. I'll put a br tag. And then let's open some more PHP. Let me make a note here. Can't change the value. Max width plus equals one. And then let's echo back max width. See what we get. Alright. Switch back over to our browser. Reload it. Oop. Sorry. Error. You can't do that. It's a syntax error. We can't do adding to this.

Right. Max width equals max width plus one. That doesn't work either. Let's just switch back and try it. Nope. Sorry. Can't do it. Let's take both of those out. Let me show you that you can't even redefine it. Alright, so let's just drop down here, we defined it here. Let's just change this, and let's say, can't even redefine it. So let's say instead of 980, let's make it now 981.

Let's try and echo that back and see what we get. Says oops, sorry. Constant max width was already defined, and then what value did it give me back? 980. It didn't change anything. It basically just objected to this completely, said sorry can't do it, and so max width stayed unchanged. It stayed constant. Now constant stays defined for the duration of the PHP script. So of course once the script ends and all the values are unset, then it can be redefined on the next run of the script. So think back to that diagram that we had of the request response cycle.

Right? When it first comes in and grabs our script and executes it, it defines the constant, the constant stays defined until it returns HTML To the user, but at that point the constant goes away. Everything in our PHP goes away at that point, until the next request response cycle. So I don't want you to think this value is forever set in stone. However, during on execution of your PHP script, that value is going to be defined and it is going to be fixed. Typically, you're only going to use them for things that don't change, things that you really want to be hard and fast. Maybe you're going to define the root path of the place where you're going to store images, right? So you want to have that as a fixed location on this hard drive. This is where you can find your image storage.

That's the kind of thing that you would use a constant for because you're not going to be varying it. You want PHP to have a fixed location for those. So most of the time, you're probably going to want to use variables. And you're going to use constants sparingly. But they're going to be very useful for saving data that's fixed.

Find answers to the most frequently asked questions about PHP with MySQL Essential Training.


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Q: This course was revised on 6/4/2013. What changed?
A: The old version of this course was 6 years old and it was time for a complete revision, using PHP 5.4. (The tutorials will work with any version of PHP and covers any differences you might encounter). The author has also added updated installation instructions for Mac OS X Mountain Lion and Windows 8. The topics and end project are the same, but the code is slightly different. It also addresses frequently asked questions from the previous version.
 
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