Page 154 - Beginning PHP 5.3

Part II: Learning the Language

Notice that, although $val was changed from “ Tolkien ” to “ Hardy ” within the loop, the original

$authors array remains untouched, as evidenced by the output from print_r() on the final line.
However, if you do want to modify the array values themselves, you can get foreach() to return a
reference to the value in the array, rather than a copy. This means that the variable within the loop points
to the value in the original array element, allowing you to change the element ’ s value simply by
changing the variable ’ s value.

To work with references to the array elements rather than copies of the values, simply add a &
(ampersand) symbol before the variable name within the foreach statement:
foreach ( $array as & $value ) {

Here ’ s the previous example rewritten to use references:

$authors = array( “Steinbeck”, “Kafka”, “Tolkien”, “Dickens” );
// Displays “Steinbeck Kafka Hardy Dickens”;
foreach ( $authors as & $val ) {
if ( $val == “Tolkien” ) $val = “Hardy”;
echo $val . “ “;
}

unset( $val );
echo “ < br/ > ”;

// Displays “Array ( [0] = > Steinbeck [1] = > Kafka [2] = > Hardy [3] = >
Dickens )”
print_r ( $authors );

Notice how, this time, the third element ’ s value in the $authors array is changed from “ Tolkien ” to

“ Hardy ” in the array itself.
By the way, the unset( $val ) line ensures that the $val variable is deleted after the loop has finished.
This is generally a good idea, because when the loop finishes, $val still holds a reference to the last
element (that is, “ Dickens “ ). If you were to change $val later in your code, you would inadvertently
alter the last element of the $authors array. By unset ting (deleting) $val , you safeguard against this
potential bug.

References are a powerful tool, and they ’ re explained in more detail in the next chapter.

Working with Multidimensional Arrays

So far, all the arrays you ’ ve worked with in this chapter have contained simple values, such as strings
and integers. However, arrays can get a lot more powerful than this. As mentioned in “ The Anatomy of
an Array, ” earlier in this chapter, PHP arrays can store values of any type. This includes resources,
objects, and, more importantly, other arrays.

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