Page 196 - Beginning PHP 5.3

Part II: Learning the Language
Finally, the script displays the sorted list of words in another fixed - width div element.

By the way, you don ’ t have to use an anonymous function in this situation. The preceding line of code
could be written as:

function sortByLength( $a, $b ) {
return strlen( $a ) - strlen( $b );
}

usort( $words, “sortByLength” );

As you can see, though, the anonymous function version is much more compact.
Working with References

You ’ ve already learned that you can pass information to a function in the form of arguments, as well as
return information from a function to its calling code using the return statement. When you do either of
these things, PHP actually passes copies of the information to and from the function; this is known as
passing and returning by value .
Most of the time this isn ’ t a problem, but sometimes you want your function to work on the original
information, rather than on a copy. Consider the following example:
function resetCounter( $c ) {
$c = 0;
}

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

echo “$counter < br/ > ”; // Displays “3”
This code defines a function, resetCounter() , that resets its argument to zero. A $counter variable is
then initialized to zero and incremented three times. As you ’ d expect, the value of $counter at this
point is 3 . resetCounter() is then called, passing in $counter , the variable to reset. However, as the
second echo statement shows, $counter has not been reset by the function. This is because the
parameter $c inside resetCounter() merely holds a copy of the information stored in $counter . So
when the function sets $c to zero, it doesn ’ t affect the value of $counter at all.

Fortunately, PHP provides a mechanism known as references that you can use to work around such issues.
A reference is a bit like a shortcut or alias to a file on your hard drive. When you create a reference to a
PHP variable, you now have two ways to read or change the variable ’ s contents — you can use the
variable name, or you can use the reference. Here ’ s a simple example that creates a reference to a variable:
$myVar = 123;
$myRef = & $myVar;
$myRef++;
echo $myRef . “ < br/ > ”; // Displays “124”

echo $myVar . “ < br/ > ”; // Displays “124”
158

9/21/09 9:00:57 AM
c07.indd 158
c07.indd 158 9/21/09 9:00:57 AM