Using PHP count() and sizeof() Functions to Count Array Elements and Object Properties

PHP provides the count() function (alias sizeof()) to obtain the number of elements in an array or the number of properties in an object.

Syntax: count ( mixed $array , int $mode ) Parameters: $array: an array or a Countable object. $mode (optional): set to COUNT_RECURSIVE (or 1) to count recursively.

Return value: the number of elements. If the argument is neither an array nor a Countable object, the function returns 1; if $array is null, it returns 0.

Usage examples:

1. Counting array elements:

<?php
$a[0] = 1;
$a[1] = 3;
$a[2] = 5;
var_dump(count($a));
var_dump(count(null));
var_dump(count(false));
?>

Output (PHP 7.2+):

int(3)
int(0)
int(1)

2. Counting object properties via the Countable interface:

<?php
class C implements Countable {
    public function count() {
        return 0;
    }
}
$a = [];
var_dump($a);
echo 'array is empty: ';
var_dump(empty($a));
echo "<br>";
$c = new C;
var_dump($c);
echo "<br>";
echo 'Countable is empty: ';
var_dump(empty($c));
echo "<br>";
?>

Output shows the array is empty (bool true) while the Countable object is not considered empty (bool false).