(PHP 4, PHP 5, PHP 7)
is_object — Finds whether a variable is an object
varThe variable being evaluated.
   Returns TRUE if var is an object,
   FALSE otherwise.
  
Example #1 is_object() example
<?php
// Declare a simple function to return an 
// array from our object
function get_students($obj)
{
    if (!is_object($obj)) {
        return false;
    }
    return $obj->students;
}
// Declare a new class instance and fill up 
// some values
$obj = new stdClass();
$obj->students = array('Kalle', 'Ross', 'Felipe');
var_dump(get_students(null));
var_dump(get_students($obj));
?>
Note:
This function will return
FALSEif used on an unserialized object where the class definition is not present (even though gettype() returns object).