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Including and requiring files

From: PHP with MySQL Essential Training

Video: Including and requiring files

One of the most useful features in PHP is the ability to include code from other files into a PHP page. It may not be obvious why that's so great, but it's an important feature because it's going to help us to stay organized and to not repeat ourselves. For example, if you define a function for one page of your site and then you need that same function again on another page. It's much better to be able to access the same function from both places, exact same code. Instead of copying and pasting the code into the second page so you can use it again. A copy is going to mean that if we find a bug or make an improvement to the function.

Including and requiring files

One of the most useful features in PHP is the ability to include code from other files into a PHP page. It may not be obvious why that's so great, but it's an important feature because it's going to help us to stay organized and to not repeat ourselves. For example, if you define a function for one page of your site and then you need that same function again on another page. It's much better to be able to access the same function from both places, exact same code. Instead of copying and pasting the code into the second page so you can use it again. A copy is going to mean that if we find a bug or make an improvement to the function.

Then we have to remember to update the code in more than one place, and that leads to bugs and code that's hard to maintain. And remember that's the whole reason that we created functions in the first place. So that we wouldn't have to repeat that code every time we needed to use it again. Instead what works better is to have a file that contains a function and then we'll include that file in both PHP pages that need it. Even better, we can have a file dedicated to functions of a certain type and put all our functions in one, easy to locate, easy to include, place. And we can do that, by using PHP's Include function.

Let's see how that works. To start with, I'm just going to open up basic .HTML and I'll do a file save as, on it. And we'll call this includes.php. Includes, so lets also make another file that we want to include the code in this file. So, lets do that, we'll do Save As on this, and this one, lets call included header. And I'm intentionally giving it a name that's very similar so that the two will show up close to each other in the list here.

So here's Included Header and here's Includes. So, for this included header, let's just have everything that's the header, everything up to the body tag. That's it. Just this HTML. Let's save that and now lets go back and open up our Includes file. And let's take all of that out. We're going to remove all of that and instead we're going to open up PHP tags, and we're going to use include, and then what do we want to include? In quotes the name of the file, included_Header.php. Now it's a PHP file even though there's not any PHP in it, that's fine.

It's not our problem. It could also be called .html, we can also include HTML files. But generally if I'm working on a PHP site, I'm going to go ahead and call all of my files that I'm working with .php. Just so that there is not a problem if I ever decide to drop in PHP, it's already ready for me. It already has PHP in the name, alright so let's just save it and then let's put something here about says the header has been included. Okay. So, let's just save that, let's go to our browser and let's open up includes.php.

There it is. The header has been included. Let's view the source. That's going to be the real test. You can see that the title is up here, Includes, that's good. Let's look at View Source. And you can see, sure enough, it included all of that header right up above it. The header's been included, and there's the body and everything that goes above it. Nice and simple, right? Include, just bring that in. That included just some basic HTML and you can do the same thing for the footer. I won't do that now but you can do that as an exercise on your own. It's just to move that to an included footer. Let's try another one now, let's just do a Save As. It doesn't really have to Save As but I'll just do Included_Functions.php.

Let's take all of this out, and let's put in a Function here. How about, function hello. Followed by a name. And that will simply return, hello, and then the name that we gave it. Exclamation point and semicolon. The hello function is now defined in our included functions file. We'll switch back. I don't need the header. What I need is, includes. There it is. And now before I even get to the header, let's do another include, which is going to be included_functions.php.

And I need semi-colons after both of those, there we go. So now we have the ability to include both of those, we should have access to this function. We should be able to call, hello. So let's try that. Let's use some PHP code here. Now it just returned a value, it didn't echo it so we're going to need to do an echo. Hello, and let's just do everyone. Now we'll put a br tag at the end, there we go. Come back over here, reload the page. There's hello everyone. Put a br tag here too just to make it nice and clean. So, there we go. It's that easy. We're including the function, it's as if it was written on this same page. It goes ahead and just processes it.

Now, there's one gotcha that I want to make sure, super clear to you. Here, we're inside PHP tags, we're in PHP mode, we do the include. Let's look over at the other file. It has PHP tags also. It's very important that you turn PHP back on in every file that's going to have PHP. 'Cuz what happens is, during this include, it turns off PHP processing. Even though we're still inside these PHP tags, when it goes to get what's in the other file. It turns off PHP processing so that this first thing in this file could be, potentially, some HTML like it was for a header.

And we need to turn it back on explicitly in this file. So just make sure that, that doesn't get you. Make sure you don't think that you're still in PHP mode here. You're not. As soon as you go to the other file, if you want to write PHP code, the same rules apply. You're going to have to turn it back on. So we've seen two good examples of what to include. Let's talk about a few others. I would say that the good things to include would be functions, because then we can define them once and only once, and they can be broken up by type. We could have our form functions, and our database functions, our general functions, right? We could have several different files of functions.

We could have layout sections of the page, the header, the footer, maybe there's a side bar that has navigation elements on. That's common to all pages, that could also be included. Reusable bits of html PHP code, this could be banner ads, page analytics. It could be little snippets of HTML/PHP, like maybe you're going to display a bunch of images. All those images are going to have titles underneath them that are all formatted a certain way. Well you could to use that throughout your site, over and over and over again. You can use Include to bring that in. And so it's useful to use Include when you want to bring in some CSS and JavaScript.

. Especially something that wasn't defined in the header of the page. Now, in addition to include, there are three variations on it that are important for us to look at. The first is require. Require does exactly the same thing as include, but it raises a fatal page error if the file can't be found. It says, look it really is required. This page will not be able to go forward if you can't get this file, so require it. Include doesn't do that. Include will try to load the file, but if it can't find it, well it'll just keep on going anyway. Now it might cause an error later on the page if we try and call a function or something that isn't defined. But include itself won't throw the error, require will. It will go ahead and say oops, we have a problem here. We can't find the file, now generally the files that you want to include are going to be present.

So, either one of these will due but, it's worth thinking about whether a file is really required or optional. For example a file that contains function or database connectivity is probably a requirement while a file that outputs a standard html footer is probably not. Another variation is include_once. Include_once keeps an array of paths to the files that it has already included. So as it includes a file, it just adds that file path to an array. And then if we asked to include it again, it will ignore it, because it sees that it has already included it before. This is great to use with functions, because we can't define functions more than once without getting an error.

And then of course there's the combination of those which is require_once. The same idea, but we're requiring it, instead of just including it. So, by using these four functions we're going to be able to keep our code well organized. And be able to bring in common code that we need, whenever we need to use it on a new page.

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This video is part of

Image for PHP with MySQL Essential Training
PHP with MySQL Essential Training

131 video lessons · 33249 viewers

Kevin Skoglund
Author

 
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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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