Programming PHP

Boolean values and NULL are not meaningfully displayed by print_r( ):
print_r(true); print "\n";
1
print_r(false); print "\n";
print_r(null); print "\n";
For this reason, var_dump( ) is preferable to print_r( ) for debugging. The var_dump( )
function displays any PHP value in a human-readable format:
var_dump(true);
bool(true)
var_dump(false);
bool(false);
var_dump(null);
bool(null);
var_dump(array('name' => Fred, 'age' => 35));
array(2) {
["name"]=>
string(4) "Fred"
["age"]=>
int(35)
}
class P {
var $name = 'Nat';
// ...
}
$p = new P;
var_dump($p);
object(p)(1) {
["name"]=>
string(3) "Nat"
}
Beware of using print_r( ) or var_dump( ) on a recursive structure such as $GLOBALS
(which has an entry for GLOBALS that points back to itself). The print_r( ) function
loops infinitely, while var_dump( ) cuts off after visiting the same element three times.
Accessing Individual Characters
The strlen( ) function returns the number of characters in a string:
$string = 'Hello, world';
$length = strlen($string); // $length is 12
You can use array syntax (discussed in detail in Chapter 5) on a string, to address
individual characters:
$string = 'Hello';
for ($i=0; $i < strlen($string); $i++) {
printf("The %dth character is %s\n", $i, $string[$i]);
}
The 0th character is H
Accessing Individual Characters | 79
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