If I don't define a constructor for a subclass, can I use the constructor of the superclass directly?

Question

Are constructors inherited or do they belong to the class they are defined in? I only have seen examples with constructors of subclasses which call superclass' constructors. This is my current code, which can give some hint about what's going on. (I will change the code according to your replies. If I can use the constructor of the superclass, I won't define a constructor for each subclass and call superclass' constructor from each.

abstract class view
{
 public $vieverid;

 function __construct($viewerid) {
  $this->viewer = $viewerid;
 }
}
class viewactor extends view{

 function __construct($viewerid) {
  $this->viewerid = $viewerid;
 }

Answer 1

According to my understanding, PHP doesn't auto-call parent's constructor if child constructor is defined. Otherwise it does.

In child constructor you have to call parent's constructor manually.

abstract class view
{
 public $vieverid;

 function __construct($viewerid) {
  $this->viewer = $viewerid;
 }
}
class viewactor extends view{

 function __construct($viewerid) {
  parent::__construct($viewerid); // manual call
  // do your stuff here...
  $this->viewerid = $viewerid;
 }

Answer 2

parent::__construct(params); use for calling superclass constructor

PHP4

PHP doesn't call constructors of the base class automatically from a constructor of a derived class. It is your responsibility to propagate the call to constructors upstream where appropriate.

PHP5

PHP doesn't call constructors of the base class if new constructor defined. If you define a constructor for derived class It is your responsibility to propagate the call to constructors upstream where appropriate. parent::__construct(params)

Constructors

abstract class view
{
 public $vieverid;

 function __construct($viewerid) {
  $this->vieverid= $viewerid;
 }
}

class viewactor extends view{

 function __construct($viewerid) {
   parent::__construct($viewerid);
   // Extra code if you want
 }
}

class viewactor_construct extends view{
    // Works in PHP5
}