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So now that you know what's a PHP array and what's a PHP variable, let's see a few functions that can help you get a good idea what's the content of a variable at any time .

print_r()

print() is a language construct, almost the same as echo and can be used instead of echo to print strings. print_r() on the other hand is a function that prints a variable recursively, meaning that it can print all elements of an array, even if it consist of other arrays.

Let's see an example:

$a = array(1, 2, 3, array(4, 5, 6));
echo $a; // prints "Array", not useful at all
print $a; // same as above
echo '<pre>'
print_r($a); // the good stuff
echo '</pre>'

So echo and print will output "Array", that's the best they can do, because they accept string input, not arrays. print_r() will output the array very nicely in a readable format, so that you know exactly what's the contents of the array. The output from the print_r() in the code above will be:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => Array
        (
            [0] => 4
            [1] => 5
            [2] => 6
        )

)

Very useful when at some point in the development, you're no longer sure what exactly is in this array.

If you give a string or a number to print_r() instead of an array, it will act as a normal print call.

var_dump()

Similarly to print_r() you can get an idea of the contents of an array by using var_dump(). In addition to what print_r() gives, it will also report the size of an array (or sub-array) and will report the type of each value.

An example use of var_dump():

$a = array('one', true, 3.14, array(4, 5, 6));
echo '<pre>'
var_dump($a);
echo '</pre>'

The result is:

array(4) {
  [0]=>
  string(3) "one"
  [1]=>
  bool(true)
  [2]=>
  float(3.14)
  [3]=>
  array(3) {
    [0]=>
    int(4)
    [1]=>
    int(5)
    [2]=>
    int(6)
  }
}

Given scalar data (not an array), var_dump() will behave similarly.

var_dump('one'); // string(3) "one"

You can pass as many values or variables to var_dump() as you want.

var_dump('one', 'two', 3);

The above will print:

string(3) "one"
string(3) "two"
int(3)

var_export()

var_export() is similar to var_dump() and print_r(), but with one significant difference - it produces valid PHP code. You can take the output and put it a PHP script as a normal PHP code.

$a = array('one', true, 3.14, array(4, 5, 6));
echo '<pre>'
var_export($a);
echo '</pre>'

The result is:

array (
  0 => 'one',
  1 => true,
  2 => 3.14,
  3 =>
  array (
    0 => 4,
    1 => 5,
    2 => 6,
  ),
)

This entry was posted on Sunday, August 10th, 2008 and is filed under PHP Tutorial. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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