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print_r

(PHP 4, PHP 5)

print_r --  打印关于变量的易于理解的信息。

描述

bool print_r ( mixed expression [, bool return] )

注: 参数 return 是在 PHP 4.3.0 的时候加上的

print_r() 显示关于一个变量的易于理解的信息。如果给出的是 string、integer 或 float，将打印变量值本身。如果给出的是 array，将会按照一定格式显示键和元素。object 与数组类似。

记住，print_r() 将把数组的指针移到最后边。使用 reset() 可让指针回到开始处。

<pre>
<?php
    $a = array ('a' => 'apple', 'b' => 'banana', 'c' => array ('x','y','z'));
    print_r ($a);
?>
</pre>

上边的代码将输出： 
<pre>
Array
(
    [a] => apple
    [b] => banana
    [c] => Array
        (
            [0] => x
            [1] => y
            [2] => z
        )
)
</pre>

如果想捕捉 print_r() 的输出，可使用 return 参数。若此参数设为 TRUE，print_r() 将不打印结果（此为默认动作），而是返回其输出。

例子 1. return 参数示例

<?php
    $b = array ('m' => 'monkey', 'foo' => 'bar', 'x' => array ('x', 'y', 'z'));
    $results = print_r ($b, true); //$results 包含了 print_r 的输出结果
?>

注: 如果想在 PHP 4.3.0 之前的版本中捕捉 print_r() 的输出，可使用输出控制函数。

注: 在 PHP 4.0.4 之前的版本中，如果给出的 array 或 object 包含了直接或间接指向自身的引用，print_r() 将永远继续下去。print_r($GLOBALS) 就是一个例子，因为 $GLOBALS 自身即是全局变量，其包含了指向自身的引用。

参见 ob_start()、var_dump() 和 var_export()。


add a note add a note User Contributed Notes
ohira (atto) web. de
13-Apr-2006 10:01
Bases on thbleys sript i use this one to log some actions.
It will return a tabbed like string which you can output or whatever.

Input fields like "Password" will not be shown.

<?php

function print_r_string($arr,$first=true,$tab=0)
{
   $output = "";
   $tabsign = ($tab) ? str_repeat('&nbsp;&nbsp;&nbsp;&nbsp;',$tab) : '';
   if ($first) $output .= "<pre><br>\n";
   foreach($arr as $key => $val)
   {
       switch (gettype($val))
       {
           case "array":
               $output .= $tabsign."[".htmlspecialchars($key)."] = array(".count($val).")<br>\n".$tabsign."(<br>\n";
               $tab++;
               $output .= print_r_string($val,false,$tab);
               $tab--;
               $output .= $tabsign.")<br>\n";
           break;
           case "boolean":
               $output .= $tabsign."[".htmlspecialchars($key)."] bool = '".($val?"true":"false")."'<br>\n";
           break;
           case "integer":
               $output .= $tabsign."[".htmlspecialchars($key)."] int = '".htmlspecialchars($val)."'<br>\n";
           break;
           case "double":
               $output .= $tabsign."[".htmlspecialchars($key)."] double = '".htmlspecialchars($val)."'<br>\n";
           break;
           case "string":
               $output .= $tabsign."[".htmlspecialchars($key)."] string = '".((stristr($key,'passw')) ? str_repeat('*', strlen($val)) : htmlspecialchars($val))."'<br>\n";
           break;
           default:
               $output .= $tabsign."[".htmlspecialchars($key)."] unknown = '".htmlspecialchars(gettype($val))."'<br>\n";
           break;
       }
   }
   if ($first) $output .= "</pre><br>\n";
   return $output;
}

echo print_r_string(array($_POST,$_GET)); // for Example
?>
sanya at hik dot hu
05-Apr-2006 10:13
I find a possibly bug, when I wanted to print the structure of a DOMDocument or a DOMDocumentType object.
print_r() outputs the object type correctly, but the properties are missing.

$doc = $imp->createDocument();
$doc->loadXML($xmlString);
print_r($doc->doctype);

the code outputs:

DOMDocumentType Object
(
)

But the subobjects of $doc->doctype exist.
reinder at fake-address dot com
01-Feb-2006 01:09
I always use this function in my code, because most of my functions return an Array or Boolean :

<?php

function printr ( $object , $name = '' ) {

   print ( '\'' . $name . '\' : ' ) ;

   if ( is_array ( $object ) ) {
       print ( '<pre>' )  ;
       print_r ( $object ) ;
       print ( '</pre>' ) ;
   } else {
       var_dump ( $object ) ;
   }

}

?>

( print_r gives no output on FALSE and that can be annoying! )
13-Dec-2005 05:00
function print_pre($var){
echo '<pre>';
print_r($var);
echo '</pre>'
}
thbley at gmail dot com
17-Nov-2005 04:10
Here is a print_r that produces xml:
(now you can expand/collapse the nodes in your browser)

<?php
header('Content-Type: text/xml; charset=UTF-8');
echo print_r_xml($some_var);

function print_r_xml($arr,$first=true) {
  $output = "";
  if ($first) $output .= "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<data>\n";
  foreach($arr as $key => $val) {
   if (is_numeric($key)) $key = "arr_".$key; // <0 is not allowed
   switch (gettype($val)) {
     case "array":
       $output .= "<".htmlspecialchars($key)." type='array' size='".count($val)."'>".
         print_r_xml($val,false)."</".htmlspecialchars($key).">\n"; break;
     case "boolean":
       $output .= "<".htmlspecialchars($key)." type='bool'>".($val?"true":"false").
         "</".htmlspecialchars($key).">\n"; break;
     case "integer":
       $output .= "<".htmlspecialchars($key)." type='integer'>".
         htmlspecialchars($val)."</".htmlspecialchars($key).">\n"; break;
     case "double":
       $output .= "<".htmlspecialchars($key)." type='double'>".
         htmlspecialchars($val)."</".htmlspecialchars($key).">\n"; break;
     case "string":
       $output .= "<".htmlspecialchars($key)." type='string' size='".strlen($val)."'>".
         htmlspecialchars($val)."</".htmlspecialchars($key).">\n"; break;
     default:
       $output .= "<".htmlspecialchars($key)." type='unknown'>".gettype($val).
         "</".htmlspecialchars($key).">\n"; break;
   }
  }
  if ($first) $output .= "</data>\n";
  return $output;
}
 
?>
jamin42b at gmail dot com
02-Sep-2005 08:52
Here's a short function that can export php arrays to javascript arrays.

<?php

function php_to_js($array, $base) {
   $js = '';
   foreach ($array as $key=>$val) {
       if (is_array($val)) {
           $js .= php_to_js($val, $base.(is_numeric($key) ? '['.$key.']' : "['".addslashes($key)."']"));
       } else {
           $js .= $base;
           $js .= is_numeric($key) ? '['.$key.']' : "['".addslashes($key)."']";
           $js .= ' = ';
           $js .= is_numeric($val) ? ''.$val.'' : "'".addslashes($val)."'";
           $js .= ";\n";
       }
   }
   return $base." = new Array();\n".$js;
}

?>

Example use:

<?php
$my_array = array('gdsag' => 4, 'hello', array(5, 6));
echo '<script>'.php_to_js($my_array).'</script>';
?>

This would output:

<script>
jsvarname = new Array();
jsvarname['gdsag'] = 4;
jsvarname[0] = 'hello';
jsvarname[1] = new Array();
jsvarname[1][0] = 5;
jsvarname[1][1] = 6;

</script>

Now the array is loaded in the browser as javascript. As you can see, it supports multidimensional arrays too.
warhog at warhog dot net
12-Aug-2005 08:01
For very long arrays I have written a little function which formats an array quite nice and uses javascript for browsing it like a tree. The function is very customizable with the $style parameter.
For me it's of great use for browsing large array's, for example when those are used in language-files in some script and so on. It may even be used in "real" scripts for the "real" front-end, cause the tree can very easily be styled (look at the function or the outputted source and you'll see what i mean).

Here's the function:

<?php

function print_r_html($arr, $style = "display: none; margin-left: 10px;")
{ static $i = 0; $i++;
  echo "\n<div id=\"array_tree_$i\" class=\"array_tree\">\n";
  foreach($arr as $key => $val)
  { switch (gettype($val))
   { case "array":
       echo "<a onclick=\"document.getElementById('";
       echo array_tree_element_$i."').style.display = ";
       echo "document.getElementById('array_tree_element_$i";
       echo "').style.display == 'block' ?";
       echo "'none' : 'block';\"\n";
       echo "name=\"array_tree_link_$i\" href=\"#array_tree_link_$i\">".htmlspecialchars($key)."</a><br />\n";
       echo "<div class=\"array_tree_element_\" id=\"array_tree_element_$i\" style=\"$style\">";
       echo print_r_html($val);
       echo "</div>";
     break;
     case "integer":
       echo "<b>".htmlspecialchars($key)."</b> => <i>".htmlspecialchars($val)."</i><br />";
     break;
     case "double":
       echo "<b>".htmlspecialchars($key)."</b> => <i>".htmlspecialchars($val)."</i><br />";
     break;
     case "boolean":
       echo "<b>".htmlspecialchars($key)."</b> => ";
       if ($val)
       { echo "true"; }
       else
       { echo "false"; }
       echo  "<br />\n";
     break;
     case "string":
       echo "<b>".htmlspecialchars($key)."</b> => <code>".htmlspecialchars($val)."</code><br />";
     break;
     default:
       echo "<b>".htmlspecialchars($key)."</b> => ".gettype($val)."<br />";
     break; }
   echo "\n"; }
  echo "</div>\n"; }

?>

The function as it is now does not support the $return parameter as print_r does and will create an endless loop like print_r did in php-versions < 4.0.3 when there is an element which contains a reference to a variable inside of the array to print out :-/

I've tested it with PHP 5.0.6 and PHP 4.2.3 - no problems except those already mentioned.

please e-mail me if you've got a solution for the problems i've mentioned, i myself are not able to solve them 'cause i don't know how the hell i can find out whether a variable is a reference or not.
nicky dot weber at siner dot de
11-Jun-2005 05:13
Print arrays formatted for a browser easily:

<?php
function print_html_r( $aData ) {
   echo nl2br( eregi_replace( " ", " ", print_r( $data, TRUE ) ) );   
}
?>
general at NOSPAMbugfoo dot com
21-Jan-2005 05:23
You can't use print_r($var, TRUE) inside a function which is a callback from ob_start() or you get the following error:
Fatal error: print_r(): Cannot use output buffering in output buffering display handlers
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