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var_dump

(PHP 4, PHP 5, PHP 7)

var_dump — 打印变量的相关信息

说明

void var_dump ( mixed $expression [, mixed $... ] )

此函数显示关于一个或多个表达式的结构信息，包括表达式的类型与值。数组将递归展开值，通过缩进显示其结构。

In PHP 5 all public, private and protected properties of objects will be returned in the output.

Tip

和直接将结果输出到浏览器一样，可使用输出控制函数来捕获当前函数的输出，然后(例如)保存到一个 string 中。

参数

expression: 你要打印的变量。

返回值

没有返回值。

范例

Example #1 var_dump() 例子

  <?php
$a  = array( 1 ,  2 , array( "a" ,  "b" ,  "c" ));
 var_dump ( $a );
 ?>

以上例程会输出：

array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  array(3) {
    [0]=>
    string(1) "a"
    [1]=>
    string(1) "b"
    [2]=>
    string(1) "c"
  }
}

  <?php

$b  =  3.1 ;
 $c  =  true ;
 var_dump ( $b ,  $c );

 ?>

以上例程会输出：

float(3.1)
bool(true)

参见

var_export() - 输出或返回一个变量的字符串表示
print_r() - 打印关于变量的易于理解的信息。

用户评论:

[#1] nikhazy dot akos at gmail dot com [2015-07-21 10:29:06]

I use this function for smaller projects.

<?php function varDump($v,$die = false) { echo '<pre>'; var_dump($v); echo '</pre><hr>'; $backtrace = debug_backtrace(); echo '<pre>'; print_r($backtrace); echo '</pre>'; if($die) die(); } ?>

[#2] Cyrus [2015-06-05 08:36:00]

Here's a function to output var_dump to PHP's error log

<?php function var_error_log( $object=null ){ ob_start(); // start buffer capture var_dump( $object ); // dump the values $contents = ob_get_contents(); // put the buffer into a variable ob_end_clean(); // end capture error_log( $contents ); // log contents of the result of var_dump( $object ) } ?>

[#3] b dot bergloev at gmail dot com [2014-10-31 23:45:12]

I post a new var_dump function with colors and collapse features. It can also adapt to terminal output if you execute it from there. No need to wrap it in a pre tag to get it to work in browsers.

<?php function dump_debug($input, $collapse=false) { $recursive = function($data, $level=0) use (&$recursive, $collapse) { global $argv; $isTerminal = isset($argv); if (!$isTerminal && $level == 0 && !defined("DUMP_DEBUG_SCRIPT")) { define("DUMP_DEBUG_SCRIPT", true); echo '<script language="Javascript">function toggleDisplay(id) {'; echo 'var state = document.getElementById("container"+id).style.display;'; echo 'document.getElementById("container"+id).style.display = state == "inline" ? "none" : "inline";'; echo 'document.getElementById("plus"+id).style.display = state == "inline" ? "inline" : "none";'; echo '}</script>'."\n"; } $type = !is_string($data) && is_callable($data) ? "Callable" : ucfirst(gettype($data)); $type_data = null; $type_color = null; $type_length = null; switch ($type) { case "String": $type_color = "green"; $type_length = strlen($data); $type_data = "\"" . htmlentities($data) . "\""; break; case "Double": case "Float": $type = "Float"; $type_color = "#0099c5"; $type_length = strlen($data); $type_data = htmlentities($data); break; case "Integer": $type_color = "red"; $type_length = strlen($data); $type_data = htmlentities($data); break; case "Boolean": $type_color = "#92008d"; $type_length = strlen($data); $type_data = $data ? "TRUE" : "FALSE"; break; case "NULL": $type_length = 0; break; case "Array": $type_length = count($data); } if (in_array($type, array("Object", "Array"))) { $notEmpty = false; foreach($data as $key => $value) { if (!$notEmpty) { $notEmpty = true; if ($isTerminal) { echo $type . ($type_length !== null ? "(" . $type_length . ")" : "")."\n"; } else { $id = substr(md5(rand().":".$key.":".$level), 0, 8); echo "<a href=\"javascript:toggleDisplay('". $id ."');\" style=\"text-decoration:none\">"; echo "" . $type . ($type_length !== null ? "(" . $type_length . ")" : "") . ""; echo "</a>"; echo " ⤵"; echo "<div id=\"container". $id ."\" style=\"display: " . ($collapse ? "" : "inline") . ";\">"; echo " "; } for ($i=0; $i <= $level; $i++) { echo $isTerminal ? "| " : "|        "; } echo $isTerminal ? "\n" : " "; } for ($i=0; $i <= $level; $i++) { echo $isTerminal ? "| " : "|        "; } echo $isTerminal ? "[" . $key . "] => " : "[" . $key . "] => "; call_user_func($recursive, $value, $level+1); } if ($notEmpty) { for ($i=0; $i <= $level; $i++) { echo $isTerminal ? "| " : "|        "; } if (!$isTerminal) { echo "</div>"; } } else { echo $isTerminal ? $type . ($type_length !== null ? "(" . $type_length . ")" : "") . " " : "" . $type . ($type_length !== null ? "(" . $type_length . ")" : "") . "  "; } } else { echo $isTerminal ? $type . ($type_length !== null ? "(" . $type_length . ")" : "") . " " : "" . $type . ($type_length !== null ? "(" . $type_length . ")" : "") . "  "; if ($type_data != null) { echo $isTerminal ? $type_data : "" . $type_data . ""; } } echo $isTerminal ? "\n" : " "; }; call_user_func($recursive, $input); } ?>

[#4] stlawson *AT* joyfulearthtech *DOT* com [2011-08-10 09:31:37]

<?php function do_dump(&$var, $var_name = NULL, $indent = NULL, $reference = NULL) { $do_dump_indent = "|    "; $reference = $reference.$var_name; $keyvar = 'the_do_dump_recursion_protection_scheme'; $keyname = 'referenced_object_name'; // So this is always visible and always left justified and readable echo "<div style='text-align:left; background-color:white; font: 100% monospace; color:black;'>"; if (is_array($var) && isset($var[$keyvar])) { $real_var = &$var[$keyvar]; $real_name = &$var[$keyname]; $type = ucfirst(gettype($real_var)); echo "$indent$var_name $type = &$real_name "; } else { $var = array($keyvar => $var, $keyname => $reference); $avar = &$var[$keyvar]; $type = ucfirst(gettype($avar)); if($type == "String") $type_color = ""; elseif($type == "Integer") $type_color = ""; elseif($type == "Double"){ $type_color = ""; $type = "Float"; } elseif($type == "Boolean") $type_color = ""; elseif($type == "NULL") $type_color = ""; if(is_array($avar)) { $count = count($avar); echo "$indent" . ($var_name ? "$var_name => ":"") . "$type ($count) $indent( "; $keys = array_keys($avar); foreach($keys as $name) { $value = &$avar[$name]; do_dump($value, "['$name']", $indent.$do_dump_indent, $reference); } echo "$indent) "; } elseif(is_object($avar)) { echo "$indent$var_name $type $indent( "; foreach($avar as $name=>$value) do_dump($value, "$name", $indent.$do_dump_indent, $reference); echo "$indent) "; } elseif(is_int($avar)) echo "$indent$var_name = $type(".strlen($avar).") $type_color".htmlentities($avar)." "; elseif(is_string($avar)) echo "$indent$var_name = $type(".strlen($avar).") $type_color\"".htmlentities($avar)."\" "; elseif(is_float($avar)) echo "$indent$var_name = $type(".strlen($avar).") $type_color".htmlentities($avar)." "; elseif(is_bool($avar)) echo "$indent$var_name = $type(".strlen($avar).") $type_color".($avar == 1 ? "TRUE":"FALSE")." "; elseif(is_null($avar)) echo "$indent$var_name = $type(".strlen($avar).") {$type_color}NULL "; else echo "$indent$var_name = $type(".strlen($avar).") ".htmlentities($avar)." "; $var = $var[$keyvar]; } echo "</div>"; } ?>

[#5] kobrasrealm at gmail dot com [2011-06-23 13:28:49]

I wrote this dandy little function for using var_dump() on HTML documents so I don't have to view the source.

<?php function htmldump($variable, $height="9em") { echo "<pre style=\"border: 1px solid #000; height: {$height}; overflow: auto; margin: 0.5em;\">"; var_dump($variable); echo "</pre>\n"; } ?>

You can pass arguments like this:
<?php $sql = mysql_query("SELECT id, name, value FROM table WHERE cond = 'value'"); $s = mysql_fetch_assoc($sql); // Dump variable containing the result of the MySQL query var_dump($s); ?>

The second parameter lets you specify the height of the box. Default is 9em, but if you're expecting a huge output you'll probably want a higher value.

<?php var_dump($s, "17em"); ?>

Happy var_dumping.

[#6] flyfy1 at gmail dot com [2011-06-22 00:22:39]

for output the var as string, include this function:
<?php function var_dump_to_string($var){ $output = "<pre>"; _var_dump_to_string($var,$output); $output .= "</pre>"; return $output; } function _var_dump_to_string($var,&$output,$prefix=""){ foreach($var as $key=>$value){ if(is_array($value)){ $output.= $prefix.$key.": \n"; _var_dump_to_string($value,$output," ".$prefix); } else{ $output.= $prefix.$key.": ".$value."\n"; } } } ?>

(say if you want to output $var to string $output)
<?php php $output = var_dump_to_string($var); ?>

[#7] divinity76 at gmail dot com [2011-04-23 06:53:00]

a html-encoded var_dump

<?php function htmlvardump(){ob_start(); $var = func_get_args(); call_user_func_array('var_dump', $var); echo htmentities(ob_get_clean());} ?>

(creds: ekneuss / mOo @ irc.freenode.net/#php )

[#8] geoff at spacevs dot com [2010-04-07 20:10:59]

var_export does not return the same output as var_dump, if you want the var_dump output in a return you can wrap the call in ob_* functions.

<?PHP ob_start(); var_dump($_SERVER); $dump = ob_get_clean(); ?>

[#9] david at exposito dot mobi [2010-02-07 11:36:35]

If you want to save exactly the content of an array into a variable to save ir later for example, use this:

<?php $xml = var_export($xml, true); ?>

You'll have in your same variable the content readable, instead of written down or anything else

[#10] ivolucien at gmail dot calm [2009-12-06 14:12:37]

For the special case where you know that you are only dealing with arrays,
<?php string implode(string $glue, array $pieces) ?>
may be all that's necessary, and the $glue parameter can be used to insert placeholders if you need to do more complex formatting. Nested arrays and such are discussed on the implode() page.

[#11] egorinsk at gmail com [2009-02-02 04:08:29]

Note that var_dump reset()'s array internal pointer!

[#12] rich dot schu at gmail dot com [2008-04-09 17:56:27]

Keep in mind if you have xdebug installed it will limit the var_dump() output of array elements and object properties to 3 levels deep.

To change the default, edit your xdebug.ini file and add the folllowing line:
xdebug.var_display_max_depth=n

More information here:
http://www.xdebug.org/docs/display

[#13] highstrike at gmail dot com [2008-01-08 05:33:08]

made 2 nifty functions based of what some people contributed here. Hope you find them usefull

usage ... call for the dump function. EG: dump($array, "Array dump");

<?php //////////////////////////////////////////////////////// // Function: dump // Inspired from: PHP.net Contributions // Description: Helps with php debugging function dump(&$var, $info = FALSE) { $scope = false; $prefix = 'unique'; $suffix = 'value'; if($scope) $vals = $scope; else $vals = $GLOBALS; $old = $var; $var = $new = $prefix.rand().$suffix; $vname = FALSE; foreach($vals as $key => $val) if($val === $new) $vname = $key; $var = $old; echo "<pre style='margin: 0px 0px 10px 0px; display: block; background: white; color: black; font-family: Verdana; border: 1px solid #cccccc; padding: 5px; font-size: 10px; line-height: 13px;'>"; if($info != FALSE) echo "$info: "; do_dump($var, '$'.$vname); echo "</pre>"; } //////////////////////////////////////////////////////// // Function: do_dump // Inspired from: PHP.net Contributions // Description: Better GI than print_r or var_dump function do_dump(&$var, $var_name = NULL, $indent = NULL, $reference = NULL) { $do_dump_indent = "|    "; $reference = $reference.$var_name; $keyvar = 'the_do_dump_recursion_protection_scheme'; $keyname = 'referenced_object_name'; if (is_array($var) && isset($var[$keyvar])) { $real_var = &$var[$keyvar]; $real_name = &$var[$keyname]; $type = ucfirst(gettype($real_var)); echo "$indent$var_name $type = &$real_name "; } else { $var = array($keyvar => $var, $keyname => $reference); $avar = &$var[$keyvar]; $type = ucfirst(gettype($avar)); if($type == "String") $type_color = ""; elseif($type == "Integer") $type_color = ""; elseif($type == "Double"){ $type_color = ""; $type = "Float"; } elseif($type == "Boolean") $type_color = ""; elseif($type == "NULL") $type_color = ""; if(is_array($avar)) { $count = count($avar); echo "$indent" . ($var_name ? "$var_name => ":"") . "$type ($count) $indent( "; $keys = array_keys($avar); foreach($keys as $name) { $value = &$avar[$name]; do_dump($value, "['$name']", $indent.$do_dump_indent, $reference); } echo "$indent) "; } elseif(is_object($avar)) { echo "$indent$var_name $type $indent( "; foreach($avar as $name=>$value) do_dump($value, "$name", $indent.$do_dump_indent, $reference); echo "$indent) "; } elseif(is_int($avar)) echo "$indent$var_name = $type(".strlen($avar).") $type_color$avar "; elseif(is_string($avar)) echo "$indent$var_name = $type(".strlen($avar).") $type_color\"$avar\" "; elseif(is_float($avar)) echo "$indent$var_name = $type(".strlen($avar).") $type_color$avar "; elseif(is_bool($avar)) echo "$indent$var_name = $type(".strlen($avar).") $type_color".($avar == 1 ? "TRUE":"FALSE")." "; elseif(is_null($avar)) echo "$indent$var_name = $type(".strlen($avar).") {$type_color}NULL "; else echo "$indent$var_name = $type(".strlen($avar).") $avar "; $var = $var[$keyvar]; } } ?>

[#14] vladimir at pixeltomorrow dot com [2007-09-10 00:45:48]

You can also use the PEAR package available at http://pear.php.net/package/Var_Dump

which parses the variable content in a very pleasant manner, a lot more easier to "follow" than the built-in var_dump() function.

Of course there are many others, but I prefer this one, because it's simply to use.

Just add at the begining of your file:

<?php require('Var_Dump.php'); // make sure the pear package path is set in php.ini Var_Dump::displayInit(array('display_mode' => 'HTML4_Text'), array('mode' => 'normal','offset' => 4)); ?>

then, instead of simply using var_dump($foo), use:

<?php Var_Dump::display($foo); ?>

Read the documentation if you're looking for different output layouts.

Cheers!
Vladimir Ghetau

[#15] thriller dot ze at gmail dot com [2007-08-21 01:49:01]

As Bryan said, it is possible to capture var_dump() output to a string. But it's not quite exact if the dumped variable contains HTML code.

You can use this instead:

<?php echo '<pre>'; // This is for correct handling of newlines ob_start(); var_dump($var); $a=ob_get_contents(); ob_end_clean(); echo htmlspecialchars($a,ENT_QUOTES); // Escape every HTML special chars (especially > and < ) echo '</pre>'; ?>

[#16] php at mikeboers dot com [2007-06-28 13:08:49]

Howdy!

I am working on a pretty large project where I needed to dump a human readable form of whatever into the log files... and I thought var_export was too difficult to read. BigueNique at yahoo dot ca has a nice solution, although I needed to NOT modify whatever was being passed to dump.

So borrowing heavily from BigueNique's (just reworked his function) and someone's idea over in the object cloning page, I came up with the following function.

It makes a complete copy of whatever object you initially pass it, including all recursive definitions and outside objects references, then does the same thing as BigueNique's function. I also heavily reworked what it output, to suit my needs.

<?php function var_log(&$varInput, $var_name='', $reference='', $method = '=', $sub = false) { static $output ; static $depth ; if ( $sub == false ) { $output = '' ; $depth = 0 ; $reference = $var_name ; $var = serialize( $varInput ) ; $var = unserialize( $var ) ; } else { ++$depth ; $var =& $varInput ; } // constants $nl = "\n" ; $block = 'a_big_recursion_protection_block'; $c = $depth ; $indent = '' ; while( $c -- > 0 ) { $indent .= '| ' ; } // if this has been parsed before if ( is_array($var) && isset($var[$block])) { $real =& $var[ $block ] ; $name =& $var[ 'name' ] ; $type = gettype( $real ) ; $output .= $indent.$var_name.' '.$method.'& '.($type=='array'?'Array':get_class($real)).' '.$name.$nl; // havent parsed this before } else { // insert recursion blocker $var = Array( $block => $var, 'name' => $reference ); $theVar =& $var[ $block ] ; // print it out $type = gettype( $theVar ) ; switch( $type ) { case 'array' : $output .= $indent . $var_name . ' '.$method.' Array ('.$nl; $keys=array_keys($theVar); foreach($keys as $name) { $value=&$theVar[$name]; var_log($value, $name, $reference.'["'.$name.'"]', '=', true); } $output .= $indent.')'.$nl; break ; case 'object' : $output .= $indent.$var_name.' = '.get_class($theVar).' {'.$nl; foreach($theVar as $name=>$value) { var_log($value, $name, $reference.'->'.$name, '->', true); } $output .= $indent.'}'.$nl; break ; case 'string' : $output .= $indent . $var_name . ' '.$method.' "'.$theVar.'"'.$nl; break ; default : $output .= $indent . $var_name . ' '.$method.' ('.$type.') '.$theVar.$nl; break ; } // $var=$var[$block]; } -- $depth ; if( $sub == false ) return $output ; } // var_log( $var, '$name' ) ; ?>

Hope it works well for you!

[#17] Bryan [2007-06-04 09:38:26]

Here's how you use output buffering to save var_dump to a string, as described in the Tip box.

<?php ob_start(); var_dump($my_variable); $my_string = ob_get_contents(); ob_end_clean(); ?>

[#18] Zak Scott [2007-05-24 10:45:48]

One of the most used approaches to this I have is:
<?php echo "<pre>"; print_r($array); // or var_dump() echo "</pre> "; ?>

This is great for debugging purposes, no need for a long-winded debug class in most cases. Unless maybe you have a gigantic project that you didn't build yourself.

[#19] kaloyan at gmail dot com [2007-04-26 11:32:32]

We can all agree that var_dump(); output is very spartan looking. The debug data needs to be organized better, and presented in a graceful way. In the era of Web 2.0 it is somewhat strange to use plain text to dump information. A DHTML powered informatiion dumping tool will be quite better - like the the open-source alternative of var_dump(); -- Krumo (http://krumo.sourceforge.net).

It renders the output using DHTML and collapsible nodes, it's layout is "skinable" and you can change it to fit your aesthetic taste. Krumo makes the output "human-readable" for real :) Plus it is compliant with both PHP4 and PHP5. Plus it detects "reference recursion". Plus you can use it to dump all various sort of data like debug back-traces, the superglobals ($_SERVER, $_ENV, $_REQUEST, $_COOKIE, $_GET, $_POST, $_SESSION), all the included files, all the declared classes, all the declared constants, all your PHP settings, all your php.ini values (if it is readable), all the loaded extensions, all the HTTP request headers, all the declared interfaces (for PHP5), all the file paths from INCLUDE_PATH, all the values of any particular INI file. Additionally it is designed to be easy to use - for example you can disable all the Krumo dumps instead of cleaning your code out of all print_r()'s and var_dump()'s. Anyway, if you check the site (http://krumo.sourceforge.net), you can found a lot of examples, demonstrations, documentation and all sort of helpful information.

[#20] thc at forestfactory dot de [2007-03-06 00:01:24]

Well, like many others I was looking for a way to get nice dumps of variables. I think I'm about to solve this once and for all; or at least for PHP 5.1. Have a look at my project HLI. http://hli.forestfactory.de

It dumps and highlights not only Arrays and Object but also DOMDocument (as XML), DB results (as table), GD-Images (as PNG), DirectoryIterators (as table), Serialized Strings and many more.

It prints backtrace, object reflection (including PHPDoc) and the position of the dump. Dumps are movable, resizeable and foldable.

It is plugin-based, so its easy to write new dump-modes for other objects/resources. It generates XML output that is parsed by XSLT to HTML and will soon be able to be handled over AJAX (I will do this the next time I program some AJAX stuff).

It runs out of the box (tested with PHP 5.1 and PHP 5.2), but this is only a 0.1 release, so please tell me if something in wrong and I'll be happy to fix it.

Oh, and it's LGPL, so just use and enjoy it. I couldn't work without it any more.

Thomas

[#21] eric at ITCbrandt dot com swap ITC/brandt [2006-12-30 22:57:27]

Very new to this and really appreciate the contributions of everyone.  I really rely on this site .  BigueNique inspired me with the last post.

I am writing an application that is WAY above my head and am buried in pages of variables and objects.  I really wanted an easier way to read them.

I had two problems - 1. The lists were too long; 2. It was hard to tell where one ended and the other began; 3.  By the time I saw my rendered forms, I forgot where my variable listing was. (Yeah, I can't count, get over it - now you know why this is so hard for me)

I had a variable dumping routine that worked better than the print_r, but elegant_dump was MUCH nicer.

I added a little bit of CSS and javascript to mine, and I have a really quick and easy way to display a colored title with a toggle control to expand or contract the variable structure and contents.

It might be too rudimentary for most of you guys, and I'm not answering anyone's question specifically, but perhaps this creative implementation will make someone's life a little easier.  At a minimum, It might be a good example of mixing in the different languages which was initially a big challenge for me.

simply call: dump_e($var,[$TracerMessage],[$ColorBackground],[$ColorContentBox]);

I have explained my functions as well as posted the required code to make it work here: http://tech.brandtitc.com/dump_e.php

It is a little too long to post in this venue.

Best Regards.

[#22] jonbarnett at gmail dot com [2006-10-02 12:25:29]

dumping objects that reference each other could lead to infinite recursion
<?php $brother = new Sibling(); $sister = new Sibling(); $brother->sister = $sister; $sister->brother = $brother; var_dump($brother); ?>

[#23] Storm [2006-08-19 10:12:37]

ul_var_dump - dump $var to <ul><li></li></ul>

<?php function ul_var_dump(&$var,$type=0) { if(!$type) echo "<ul type='circle' style='border:1px solid #a0a0a0;padding-bottom:4px;padding-right:4px'>\n<li>"; if(is_array($var)) { echo "[array][".count($var)."]"; echo "<ul type='circle' style='border:1px solid #a0a0a0;padding-bottom:4px;padding-right:4px'>\n"; foreach($var as $k=>$v) { echo "<li>\"{$k}\"=>"; ul_var_dump(&$v,1); } echo "</ul>\n"; } else echo "[".gettype($var)."][{$var}]</li>\n"; if(!$type) echo "</ul>\n"; } ?>

[#24] ospinto at hotmail dot com [2005-08-06 21:43:01]

Just created this neat class that dumps a variable in a colored tabular structure similar to the cfdump tag in Coldfusion. Very easy to use and makes it so much easier to see the contents of variable. For examples and download, visit http://dbug.ospinto.com

[#25] edwardzyang at thewritingpot dot com [2005-03-20 14:06:13]

If you're like me and uses var_dump whenever you're debugging, you might find these two "wrapper" functions helpful.

This one automatically adds the PRE tags around the var_dump output so you get nice formatted arrays.

<?php function var_dump_pre($mixed = null) { echo '<pre>'; var_dump($mixed); echo '</pre>'; return null; } ?>

This one returns the value of var_dump instead of outputting it.

<?php function var_dump_ret($mixed = null) { ob_start(); var_dump($mixed); $content = ob_get_contents(); ob_end_clean(); return $content; } ?>

Fairly simple functions, but they're infinitely helpful (I use var_dump_pre() almost exclusively now).

[#26] anon [2005-01-28 06:31:38]

var_dump(get_defined_vars());
will dump all defined variables to the browser.