PHP $this variable

Question

I am reading some PHP code that I could not understand:

class foo {
  function select($p1, $dbh=null) {
    if ( is_null($dbh) )
        $dbh = $this->dbh         


        

Answer 1

What is the value of $this->dbh

It will have the default value, if assigned else "null"

Is it a local variable for function select()? If it is, then why get() function can use this variable?

It is the property of foo class, not the local variable, so it will be available to all the methods of the foo class

Does it belongs class foo's data member? If it is, why there is no declaration for $dbh in this class?

Yes it does belong to the foo's data member, you don't see any declaration because, PHP is not strict about requiring class property declarations.