PHP/MySQL Tutorial
Welcome to the third and final lesson for this tutorial. If you’ve gone through Lesson 1 and Lesson 2, you already know the essentials for installing and writing useful scripts with MySQL and PHP. We’re going to look at some useful PHP functions that should make your life a lot easier. First, let’s look at include files.
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We all know the basics of includes, right? Contents of an external file are referenced and imported into the main file. It’s pretty easy: You call a file and it’s included. When we do this in PHP there are two functions we need to talk about: include() and require(). The difference between these two functions is subtle but important, so let’s take a closer look. The require() function works in a XSSI-like way; files are included as part of the original document as soon as that file is parsed, regardless of its location in the script. So if you decide to place a require() function inside a conditional loop, the external file will be included even if that part of the conditional loop is false.
The include() function imports the referenced file each time it is encountered. If it’s not encountered, PHP won’t bother with it. This means that you can use include in loops and conditional statements, and they’ll work exactly as planned.
Finally, if you use require() and the file you’re including does not exist, your script will halt and produce an error. If you use include(), your script will generate a warning, but carry on. You can test this yourself by trying the following script. Run the script, then replace include() with require() and compare the results.
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