PHP Question: Print Object

28th April 2011 - 3 minutes read time

Note: This post is over a year old and so the information contained here might be out of date. If you do spot something please leave a comment and I will endeavour to correct.

Question

The following code was executed.

<?php
class MyClass {
  private $foo = "bar";
}
 
$myObject = new MyClass();
echo $myObject;

Which produced the following error.

Catchable fatal error: Object of class MyClass could not be converted to string in test.php on line 7
 
Call Stack:
    0.0011     323736   1. {main}() /test.php:0

How can the code be simply changed to prevent this error and produce some form of result?

Answer

The easiest way to rewrite this code and to actually print out the object properly is to use the __toString() magic method. This method must return a string and is automatically called an object is printed out. The example code can therefore be rewritten like this:

<?php
class MyClass {
  private $foo = "bar";
 
  public function __toString() {
    return $this->foo;
  }
}
 
$myObject = new MyClass();
echo $myObject;

This stops the error occurring and will produce the output below.

bar

The __toString() function is useful for both debug purposes but also for decorating output. For example, we could have a User class that would print out the user's information, and a HtmlUser decorator class that prints out the user's information with surrounding HTML tags. This would be written like this:

<?php
class User {
 
  public $_username;
  public $_forename;
  public $_surname;
  public $_created;
 
  public function __construct() {
    $this->_username = 'user1';
    $this->_forename = 'John';
    $this->_surname = 'Doe';
    $this->_created = time();
  }
 
  public function __toString() {
    $output = '';
 
    $output .= "Username = " . $this->_username . "\n";
    $output .= "Forename = " . $this->_forename . "\n";
    $output .= "Surname = " . $this->_surname . "\n";
    $output .= "Created = " . $this->_created . "\n";
 
    return $output;
  }
 
}
 
class HtmlUser {
 
  protected $user;
 
  public function __construct(User $user) {
    $this->user = $user;
  }
 
  public function __toString() {
    $output = "<ul>\n";
 
    $output .= "\t<li><strong>Username</strong> " . $this->user->_username . "</li>\n";
    $output .= "\t<li><strong>Forename</strong> " . $this->user->_forename . "</li>\n";
    $output .= "\t<li><strong>Surname</strong> " . $this->user->_surname . "</li>\n";
    $output .= "\t<li><strong>Created</strong> " . $this->user->_created . "</li>\n";
 
    $output .= "</ul>";
 
    return $output;
  }
 
}
 
$user = new User();
$htmlUser = new HtmlUser($user);
echo $htmlUser;

This produces the following output:

<ul>
	<li><strong>Username</strong> user1</li>
	<li><strong>Forename</strong> John</li>
	<li><strong>Surname</strong> Doe</li>
	<li><strong>Created</strong> 1304196043</li>
</ul>

PHP

Comments

Permalink

echo ( is_object( $myObject ) ) ? 'Sorry! We have an object here!' : $myObject ;

Add new comment

Related Content

Creating A Game With PHP Part 4: Side Scrolling Shooter

As another step up from the game of snake I created in my last post I decided to try my hand at creating a side scrolling shooter. Just like my other posts, this is an ASCII based game played on the command line.

A side scrolling shooter, if you didn't already know, moves a scene from right to left across the screen with enemies moving with the scene towards the player's ship, which is on the left hand side of the scene. The player can fire bullets towards the enemies so remove them from the scene.

Seeding Random Numbers in PHP

Computers are not that great at creating random numbers as the methods they use are deterministic. That is, they start from a number (called a seed) and apply maths to that number to generate pseudorandom numbers. Most random numbers generated by computers programs use a seed provided by the system, which is generally the current time. If you can guess the initial value then you can start to work out what the random sequence of numbers generated is. Most random numbers, are therefore not suitable for encryption.

PHP: Find An Array Sequence In An Array

I was looking for a function that searched an array for another array, and after not finding one I decided to write it. What I was looking for was a function that took a smaller array and searched for that exact sequence of items in a larger array. As it happens, PHP does have a number of array search functions, but they didn't produce the correct result.

PHP Live Regex

When creating regular expressions for PHP I tend to use the awesome tool PHP Live Regex.

This tool has really helped me over the last couple of years to create regular expressions for many of the projects I've been working on. Everything from validation functions to formatters that use regular expressions have had their expressions worked out using this tool. I even use it for testing one off expressions where I just need to find/replace in a file.

PHP Strict Types

In December 2015, PHP 7 introduced scalar type declarations and with it the strict_types flag. This flag can be used to enforce the type of value passed to functions. Although I have seen it in action in the past, I have never actually used it before so I decided to look into it a little to see what it was about.

PHP instanceof Operator Tips

The instanceof operator in PHP is great at making sure you are looking at a type of object before acting on it. Whilst it's straightforward to use on its own, using it can lead to some undesirable side effects.

As a basic example, let's create a couple of interfaces and classes to show the instanceof operator in action. Rather than just have some test names I am using object names that you might find in a system. This consists of User and Order that might form part of a commerce system.