Q:

Using print_r and var_dump with circular reference

I'm using the MVC framework Symfony, and it seems a lot of the built-in objects I want to debug have circular references. This makes it impossible to print the variables with print_r() or var_dump() (since they follow circular references ad infinitum or until the process runs out of memory, whichever comes first).
Instead of writing my own print_r clone with some intelligence, are there better alternatives out there? I only want to be able to print a variable (object, array or scalar), either to a log file, http header or the web page itself.
Edit: to clarify what the problem is, try this code:
<?php

class A
{
    public $b;
    public $c;

    public function __construct()
    {
        $this->b = new B();
        $this->c = new C();
    }
}

class B
{
    public $a;

    public function __construct()
    {
        $this->a = new A();
    }
}

class C
{
}

ini_set('memory_limit', '128M');
set_time_limit(5);

print_r(new A());
#var_dump(new A());
#var_export(new A());

It doesn't work with print_r(), var_dump() or var_export(). The error message is:

PHP Fatal error:  Allowed memory size of 134217728 bytes exhausted (tried to allocate 523800 bytes) in print_r_test.php on line 10

A:

Doctrine have the same service class.
Example of usage:
<?php echo "<pre>"; \Doctrine\Common\Util\Debug::dump($result, 4); echo "</pre>";?>

A:

We are using the PRADO Framework and it has a built in class called "TVarDumper" which can handle such complex objects pretty well - it even can format it in nice HTML incl. Syntax Highlighting. You can get that class from HERE.

A:

TVarDumper
TVarDumper is intended to replace the buggy PHP function var_dump and print_r, since it can correctly identify the recursively referenced objects in a complex object structure. It also has a recursive depth control to avoid indefinite recursive display of some peculiar variables.
Check TVarDumper.php:
<?php
/**
 * TVarDumper class file
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.pradosoft.com/
 * @copyright Copyright &copy; 2005-2013 PradoSoft
 * @license http://www.pradosoft.com/license/
 * @version $Id$
 * @package System.Util
 */

/**
 * TVarDumper class.
 *
 * TVarDumper is intended to replace the buggy PHP function var_dump and print_r.
 * It can correctly identify the recursively referenced objects in a complex
 * object structure. It also has a recursive depth control to avoid indefinite
 * recursive display of some peculiar variables.
 *
 * TVarDumper can be used as follows,
 * <code>
 *   echo TVarDumper::dump($var);
 * </code>
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @version $Id$
 * @package System.Util
 * @since 3.0
 */
class TVarDumper
{
    private static $_objects;
    private static $_output;
    private static $_depth;

    /**
     * Converts a variable into a string representation.
     * This method achieves the similar functionality as var_dump and print_r
     * but is more robust when handling complex objects such as PRADO controls.
     * @param mixed variable to be dumped
     * @param integer maximum depth that the dumper should go into the variable. Defaults to 10.
     * @return string the string representation of the variable
     */
    public static function dump($var,$depth=10,$highlight=false)
    {
        self::$_output='';
        self::$_objects=array();
        self::$_depth=$depth;
        self::dumpInternal($var,0);
        if($highlight)
        {
            $result=highlight_string("<?php\n".self::$_output,true);
            return preg_replace('/&lt;\\?php<br \\/>/','',$result,1);
        }
        else
            return self::$_output;
    }

    private static function dumpInternal($var,$level)
    {
        switch(gettype($var))
        {
            case 'boolean':
                self::$_output.=$var?'true':'false';
                break;
            case 'integer':
                self::$_output.="$var";
                break;
            case 'double':
                self::$_output.="$var";
                break;
            case 'string':
                self::$_output.="'$var'";
                break;
            case 'resource':
                self::$_output.='{resource}';
                break;
            case 'NULL':
                self::$_output.="null";
                break;
            case 'unknown type':
                self::$_output.='{unknown}';
                break;
            case 'array':
                if(self::$_depth<=$level)
                    self::$_output.='array(...)';
                else if(empty($var))
                    self::$_output.='array()';
                else
                {
                    $keys=array_keys($var);
                    $spaces=str_repeat(' ',$level*4);
                    self::$_output.="array\n".$spaces.'(';
                    foreach($keys as $key)
                    {
                        self::$_output.="\n".$spaces."    [$key] => ";
                        self::$_output.=self::dumpInternal($var[$key],$level+1);
                    }
                    self::$_output.="\n".$spaces.')';
                }
                break;
            case 'object':
                if(($id=array_search($var,self::$_objects,true))!==false)
                    self::$_output.=get_class($var).'#'.($id+1).'(...)';
                else if(self::$_depth<=$level)
                    self::$_output.=get_class($var).'(...)';
                else
                {
                    $id=array_push(self::$_objects,$var);
                    $className=get_class($var);
                    $members=(array)$var;
                    $keys=array_keys($members);
                    $spaces=str_repeat(' ',$level*4);
                    self::$_output.="$className#$id\n".$spaces.'(';
                    foreach($keys as $key)
                    {
                        $keyDisplay=strtr(trim($key),array("\0"=>':'));
                        self::$_output.="\n".$spaces."    [$keyDisplay] => ";
                        self::$_output.=self::dumpInternal($members[$key],$level+1);
                    }
                    self::$_output.="\n".$spaces.')';
                }
                break;
        }
    }
}

XDebug var_dump
Use XDebug PHP extension, and it'll detect and ignore the circular references, e.g.:
echo xdebug_var_dump($object);

print_r + array_slice
As per this post, you may try:
print_r(array_slice($desiredArray, 0, 4));

features_var_export
Use the following function which is part of Features module for Drupal (features.export.inc):
/**
 * Export var function
 */
function features_var_export($var, $prefix = '', $init = TRUE, $count = 0) {
  if ($count > 50) {
    // Recursion depth reached.
    return '...';
  }

  if (is_object($var)) {
    $output = method_exists($var, 'export') ? $var->export() : features_var_export((array) $var, '', FALSE, $count+1);
  }
  else if (is_array($var)) {
    if (empty($var)) {
      $output = 'array()';
    }
    else {
      $output = "array(\n";
      foreach ($var as $key => $value) {
        // Using normal var_export on the key to ensure correct quoting.
        $output .= "  " . var_export($key, TRUE) . " => " . features_var_export($value, '  ', FALSE, $count+1) . ",\n";
      }
      $output .= ')';
    }
  }
  else if (is_bool($var)) {
    $output = $var ? 'TRUE' : 'FALSE';
  }
  else if (is_int($var)) {
    $output = intval($var);
  }
  else if (is_numeric($var)) {
    $floatval = floatval($var);
    if (is_string($var) && ((string) $floatval !== $var)) {
      // Do not convert a string to a number if the string
      // representation of that number is not identical to the
      // original value.
      $output = var_export($var, TRUE);
    }
    else {
      $output = $floatval;
    }
  }
  else if (is_string($var) && strpos($var, "\n") !== FALSE) {
    // Replace line breaks in strings with a token for replacement
    // at the very end. This protects whitespace in strings from
    // unintentional indentation.
    $var = str_replace("\n", "***BREAK***", $var);
    $output = var_export($var, TRUE);
  }
  else {
    $output = var_export($var, TRUE);
  }

  if ($prefix) {
    $output = str_replace("\n", "\n$prefix", $output);
  }

  if ($init) {
    $output = str_replace("***BREAK***", "\n", $output);
  }

  return $output;
}

Usage:
echo features_var_export($object);

Serialize
Use serialize to dump the object in serialized representation, e.g.:
echo serialize($object);

JSON Encode
Use json_encode to convert it into JSON format, e.g.:
echo json_encode($object);

See also: Test if variable contains circular references

