Page 197 - Beginning PHP 5.3

Chapter 7: Functions
First a new variable, $myVar , is initialized with the value 123 . Next, a reference to $myVar is created,
and the reference is stored in the variable $myRef . Note the ampersand ( & ) symbol after the equals sign;
using this symbol creates the reference.
The next line of code adds one to the value of $myRef . Because $myRef actually points to the same data
as $myVar , both $myRef and $myVar now contain the value 124 , as shown by the two echo statements.

Now that you know what references are, and how to create them, it ’ s time to look at how you can pass
references into and out of your functions.

Passing References to Your Own Functions
By passing a reference to a variable as an argument to a function, rather than the variable itself, you pass
the argument by reference , rather than by value. This means that the function can now alter the original
value, rather than working on a copy.

To get a function to accept an argument as a reference rather than a value, put an ampersand ( & ) before
the parameter name within the function definition:

function myFunc( & $aReference ){
// (do stuff with $aReference)

}
Now, whenever a variable is passed to myFunc() , PHP actually passes a reference to that variable, so
that myFunc() can work directly with the original contents of the variable, rather than a copy.

Now that you know this, you can fix the earlier counter example by using a reference:

function resetCounter( & $c ) {
$c = 0;
}

$counter = 0;
$counter++;
$counter++;
$counter++;
echo “$counter < br/ > ”; // Displays “3”
resetCounter( $counter );
echo “$counter < br/ > ”; // Displays “0”

The only change in the script is in the first line:

function resetCounter( & $c ) {

Adding the ampersand before the $c causes the $c parameter to be a reference to the passed argument
( $counter in this example). Now, when the function sets $c to zero, it ’ s actually setting the value of
$counter to zero, as can be seen by the second echo statement.

Many built - in PHP functions accept references in this way. For example, PHP ’ s sort() function, which you
met in the previous chapter, changes the array you pass to it, sorting its elements in order. The array is passed
in by reference rather than by value, so that the function can change the array itself, rather than a copy of it.

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