[HELP] Why No Display?

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  • hide2may
    New Member
    • Jul 2009
    • 5
    #1

    [HELP] Why No Display?

    Hi there,

    I'm learning from PHP5 Power Programming by Gutmans, Bakken & Rethans and have come to p.58. The book says the output is:

    Judy
    Joe

    However I get nothing from neither IE8 nor FF3 instead!
    My machine is XP + PHP5 + Apache2.2. The error message is:

    Catchable fatal error: Object of class Person could not be converted to string in C:\Program Files\...\PHP5 PP\58.php on line 24

    Any clue?

    Thanks in advance,
    -hide2may

    // Here is the source:
    Code:
    <html>
<title>PHP5 Power Programming</title>
<head>P.58</head>
<body>
<?php

   error_reporting(E_ALL);
   ini_set('display_errors', true);

   class Person {

      function _construct($name) {
         $this->name = $name;
      }

      function getName() {
         return $this->name;
      }

      private $name;
   
   };

   $judy = new Person("Judy") . "\n";  // <---- this is line 24
   $joe = new Person("Joe") . "\n";

   print $judy->getName();
   print $joe->getName();

?>
</body>
</html>
    Tags: None
    • Dormilich
      Recognized Expert Expert
      • Aug 2008
      • 8694
      #2
      the problem is
      Code:
      $judy = new Person("Judy")[U] . "\n"[/U];
      if you instantiate an object, you cannot apply any other operation at the same time.

      Code:
      // correct
$judy = new Person("Judy");
      in your case the string concatenation forces new Person("Judy") to be converted to a string, which doesn’t work.

      guess it’s a printing mistake, should probably be like in the previous example (and this would actually make sense)
      Code:
      $judy = new Person("Judy"); 
$joe = new Person("Joe"); 
print $judy->getName() . "\n"; 
print $joe->getName() . "\n";
      and one additional note
      Code:
      $x = new Sample;
// is the same as
$x = new Sample();
      Originally posted by hide2may
      However I get nothing from neither IE8 nor FF3 instead!
      since PHP runs on the server both browsers get the same output (unless you start working with HTTP/1.1* data (like Accept header…))

      * see RFC 2616

        Comment

        • Markus
          Recognized Expert Expert
          • Jun 2007
          • 6092
          #3
          However, you can have a __toString() implementation that will allow you to do what you attempt above (although I don't think it's quite the right way to do it).

          Code:
          	class Person {
	
		private $person;
		
		public function __construct($name) {
			$this->person = $name;
		}
		
		public function __toString() {
			return $this->person;
		}
	
	}
	
	$person = new Person("mark") . " - hi";
	
	echo $person;

            Comment

            • hide2may
              New Member
              • Jul 2009
              • 5
              #4
              Oh, no, Dormilich! Even I changed the relevant code to the followings, still get no display! How come?

              ...
              $judy = new Person("Judy");
              $joe = new Person("Joe");

              print $judy->getName( );
              print $joe->getName( );

                Comment

                • Dormilich
                  Recognized Expert Expert
                  • Aug 2008
                  • 8694
                  #5
                  Originally posted by Markus
                  … that will allow you to do what you attempt above.
                  even book printers can make mistakes. I don’t think hide2may actually meant to do that.

                    Comment

                    • hide2may
                      New Member
                      • Jul 2009
                      • 5
                      #6
                      No, Dormilich, I don't want to do Markus' way which is too far for me as a PHP beginner. My problem now becomes that even I changed those 4 lines mentioned by Dormilich in post 2, I still don't get the desired output, though the error message has gone. So, how do I proceed? Thanks again ^.^

                      The 4 lines have already been changed to:

                      $judy = new Person("Judy");
                      $joe = new Person("Joe");

                      print $judy->getName( ) . "\n";
                      print $joe->getName( ) . "\n";

                        Comment

                        • hide2may
                          New Member
                          • Jul 2009
                          • 5
                          #7
                          Ah... the same thing happens again in p.70!
                          The book says the output is:

                          In Ancestor constructor
                          In Child constructor

                          But in my machine: No desired display, no error message!
                          I doubt that it has something to do with _construct( )
                          any ideas, please?

                          // Here is the code:
                          Code:
                          <html>
<title>PHP5 Power Programming</title>
<head>P.70</head>
<body>
<?php

   error_reporting(E_ALL);
   ini_set('display_errors', true);

   class Ancestor {
      const NAME = "Ancestor";
      function _construct() {
         print "In " . self::NAME . " constructor\n";
      }
   }

   class Child extends Ancestor {
      const NAME = "Child";
      function _construct() {
         parent::_construct();
         print "In " . self::NAME . " constructor\n";
      }
   }

   $obj = new Child();
?>
</body>
</html>

                            Comment

                            • Dormilich
                              Recognized Expert Expert
                              • Aug 2008
                              • 8694
                              #8
                              all the magical methods (__construct(), __destruct(), __get(), __set(), __call(), …) are written with 2 underscores in the beginning.

                              for the correct syntax also refer to the manual

                              PS: please use &#91;code] &#91;/code] tags when posting code

                                Comment

                                • Markus
                                  Recognized Expert Expert
                                  • Jun 2007
                                  • 6092
                                  #9
                                  Easy mistake - magic methods use two preceding underscores.

                                  Code:
                                  public function __construct()

// not!
public function _construct()

                                    Comment

                                    • Markus
                                      Recognized Expert Expert
                                      • Jun 2007
                                      • 6092
                                      #10
                                      Whoops - beaten to it :P

                                        Comment

                                        • hide2may
                                          New Member
                                          • Jul 2009
                                          • 5
                                          #11
                                          okay, that works!
                                          thanks man \O/

                                            Comment

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