Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

Chapter 5. PHP Functions and Objects

The basic requirements of any programming language include somewhere to store data, a means of directing program flow, and a few bits and pieces such as expression evaluation, file management, and text output. PHP has all these, plus tools like else and elseif to make life easier. But even with all these in your toolkit, programming can be clumsy and tedious, especially if you have to rewrite portions of very similar code each time you need them.

That’s where functions and objects come in. As you might guess, a function is a set of statements that performs a particular function and—optionally—returns a value. You can pull out a section of code that you have used more than once, place it into a function, and call the function by name when you want the code.

Functions have many advantages over contiguous, inline code:

• Less typing is involved.

• Functions reduce syntax and other programming errors.

• They decrease the loading time of program files.

• They also decrease execution time, because each function is compiled only once, no matter how often you call it.

• Functions accept arguments and can therefore be used for general as well as specific cases.

Objects take this concept a step further. An object incorporates one or more functions, and the data they use, into a single structure called a class.

In this chapter, you’ll learn all about using functions, from defining and calling them to passing arguments back and forth. With that knowledge under your belt, you’ll ...