Programming PHP

Storing Data in Arrays

Storing a value in an array will create the array if it didn’t already exist, but trying to retrieve a value from an array that hasn’t been defined yet won’t create the array. For example:

// $addresses not defined before this point
echo $addresses[0];                    // prints nothing
echo $addresses;                       // prints nothing
$addresses[0] = '[e-mail]';
echo $addresses;                       // prints "Array"

Using simple assignment to initialize an array in your program leads to code like this:

$addresses[0] = '[e-mail]';
$addresses[1] = '[e-mail]';
$addresses[2] = '[e-mail]';
// ...

That’s an indexed array, with integer indexes beginning at 0. Here’s an associative array:

$price['Gasket'] = 15.29;
$price['Wheel']  = 75.25;
$price['Tire']   = 50.00;
// ...

An easier way to initialize an array is to use the array( ) construct, which builds an array from its arguments:

$addresses = array('[e-mail]', '[e-mail]',
                   '[e-mail]');

To create an associative array with array( ), use the => symbol to separate indexes from values:

$price = array('Gasket' => 15.29,
               'Wheel'  => 75.25,
               'Tire'   => 50.00);

Notice the use of whitespace and alignment. We could have bunched up the code, but it wouldn’t have been as easy to read:

$price = array('Gasket'=>15.29,'Wheel'=>75.25,'Tire'=>50.00);

To construct an empty array, pass no arguments to array( ):

$addresses = array(  );

You can specify an initial key with => and then a list of values. The values are inserted into ...