PHP - Manual: var_dump

2025-11-01

var_export »

« unset

var_dump

(PHP 4, PHP 5, PHP 7, PHP 8)

var_dump — 打印变量的相关信息

说明

var_dump(mixed $value, mixed ...$values): void

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。数组和对象将递归展开值，通过缩进显示其结构。

对象的所有公共、私有和受保护的属性都会在输出中返回，除非该对象实现了 __debugInfo() 方法。

小技巧

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

value: 要打印的表达式。
values: 更多要打印的表达式。

返回值

没有返回值。

示例

示例 #1 var_dump() 例子

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

以上示例会输出：

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);

?>

以上示例会输出：

float(3.1)
bool(true)

参见

print_r() - 打印人类可读的变量信息
debug_zval_dump() - 将表示内部 zval 结构的字符串转储到输出
var_export() - 输出或返回变量的可解析字符串表示
__debugInfo()

发现了问题？

了解如何改进此页面 • 提交拉取请求 • 报告一个错误

＋添加备注

用户贡献的备注 16 notes

down

153

rich dot schu at gmail dot com ¶

16 years ago

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

down

133

edwardzyang at thewritingpot dot com ¶

19 years ago

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).

down

b dot bergloev at gmail dot com ¶

10 years ago

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 "<span style='color:#666666'>" . $type . ($type_length !== null ? "(" . $type_length . ")" : "") . "</span>";
                        echo "</a>";
                        echo "<span id=\"plus". $id ."\" style=\"display: " . ($collapse ? "inline" : "none") . ";\">&nbsp;&#10549;</span>";
                        echo "<div id=\"container". $id ."\" style=\"display: " . ($collapse ? "" : "inline") . ";\">";
                        echo "<br />";
                    }

                    for ($i=0; $i <= $level; $i++) {
                        echo $isTerminal ? "|    " : "<span style='color:black'>|</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;";
                    }

                    echo $isTerminal ? "\n" : "<br />";
                }

                for ($i=0; $i <= $level; $i++) {
                    echo $isTerminal ? "|    " : "<span style='color:black'>|</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;";
                }

                echo $isTerminal ? "[" . $key . "] => " : "<span style='color:black'>[" . $key . "]&nbsp;=>&nbsp;</span>";

call_user_func($recursive, $value, $level+1);
            }

            if ($notEmpty) {
                for ($i=0; $i <= $level; $i++) {
                    echo $isTerminal ? "|    " : "<span style='color:black'>|</span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;";
                }

                if (!$isTerminal) {
                    echo "</div>";
                }

            } else {
                echo $isTerminal ? 
$type . ($type_length !== null ? "(" . $type_length . ")" : "") . "  " : 
"<span style='color:#666666'>" . $type . ($type_length !== null ? "(" . $type_length . ")" : "") . "</span>&nbsp;&nbsp;";
            }

        } else {
            echo $isTerminal ? 
$type . ($type_length !== null ? "(" . $type_length . ")" : "") . "  " : 
"<span style='color:#666666'>" . $type . ($type_length !== null ? "(" . $type_length . ")" : "") . "</span>&nbsp;&nbsp;";

            if ($type_data != null) {
                echo $isTerminal ? $type_data : "<span style='color:" . $type_color . "'>" . $type_data . "</span>";
            }
        }

        echo $isTerminal ? "\n" : "<br />";
    };

call_user_func($recursive, $input);
}
?>

down

anon ¶

20 years ago

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

down

stlawson *AT* joyfulearthtech *DOT* com ¶

13 years ago

<?php
/**
 * Better GI than print_r or var_dump -- but, unlike var_dump, you can only dump one variable.  
 * Added htmlentities on the var content before echo, so you see what is really there, and not the mark-up.
 * 
 * Also, now the output is encased within a div block that sets the background color, font style, and left-justifies it
 * so it is not at the mercy of ambient styles.
 *
 * Inspired from:     PHP.net Contributions
 * Stolen from:       [highstrike at gmail dot com]
 * Modified by:       stlawson *AT* JoyfulEarthTech *DOT* com 
 *
 * @param mixed $var  -- variable to dump
 * @param string $var_name  -- name of variable (optional) -- displayed in printout making it easier to sort out what variable is what in a complex output
 * @param string $indent -- used by internal recursive call (no known external value)
 * @param unknown_type $reference -- used by internal recursive call (no known external value)
 */
function do_dump(&$var, $var_name = NULL, $indent = NULL, $reference = NULL)
{
$do_dump_indent = "<span style='color:#666666;'>|</span> &nbsp;&nbsp; ";
$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 <span style='color:#666666'>$type</span> = <span style='color:#e87800;'>&amp;$real_name</span><br>";
    }
    else
    {
$var = array($keyvar => $var, $keyname => $reference);
$avar = &$var[$keyvar];

$type = ucfirst(gettype($avar));
        if($type == "String") $type_color = "<span style='color:green'>";
        elseif($type == "Integer") $type_color = "<span style='color:red'>";
        elseif($type == "Double"){ $type_color = "<span style='color:#0099c5'>"; $type = "Float"; }
        elseif($type == "Boolean") $type_color = "<span style='color:#92008d'>";
        elseif($type == "NULL") $type_color = "<span style='color:black'>";

        if(is_array($avar))
        {
$count = count($avar);
            echo "$indent" . ($var_name ? "$var_name => ":"") . "<span style='color:#666666'>$type ($count)</span><br>$indent(<br>";
$keys = array_keys($avar);
            foreach($keys as $name)
            {
$value = &$avar[$name];
do_dump($value, "['$name']", $indent.$do_dump_indent, $reference);
            }
            echo "$indent)<br>";
        }
        elseif(is_object($avar))
        {
            echo "$indent$var_name <span style='color:#666666'>$type</span><br>$indent(<br>";
            foreach($avar as $name=>$value) do_dump($value, "$name", $indent.$do_dump_indent, $reference);
            echo "$indent)<br>";
        }
        elseif(is_int($avar)) echo "$indent$var_name = <span style='color:#666666'>$type(".strlen($avar).")</span> $type_color".htmlentities($avar)."</span><br>";
        elseif(is_string($avar)) echo "$indent$var_name = <span style='color:#666666'>$type(".strlen($avar).")</span> $type_color\"".htmlentities($avar)."\"</span><br>";
        elseif(is_float($avar)) echo "$indent$var_name = <span style='color:#666666'>$type(".strlen($avar).")</span> $type_color".htmlentities($avar)."</span><br>";
        elseif(is_bool($avar)) echo "$indent$var_name = <span style='color:#666666'>$type(".strlen($avar).")</span> $type_color".($avar == 1 ? "TRUE":"FALSE")."</span><br>";
        elseif(is_null($avar)) echo "$indent$var_name = <span style='color:#666666'>$type(".strlen($avar).")</span> {$type_color}NULL</span><br>";
        else echo "$indent$var_name = <span style='color:#666666'>$type(".strlen($avar).")</span> ".htmlentities($avar)."<br>";

$var = $var[$keyvar];
    }

    echo "</div>";
}
?>

down

thriller dot ze at gmail dot com ¶

17 years ago

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>';
?>

down

egorinsk at gmail com ¶

16 years ago

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

down

highstrike at gmail dot com ¶

17 years ago

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($info != FALSE) echo "<b style='color: red;'>$info:</b><br>";
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 = "<span style='color:#eeeeee;'>|</span> &nbsp;&nbsp; ";
$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 <span style='color:#a2a2a2'>$type</span> = <span style='color:#e87800;'>&amp;$real_name</span><br>";
    }
    else
    {
$var = array($keyvar => $var, $keyname => $reference);
$avar = &$var[$keyvar];

$type = ucfirst(gettype($avar));
        if($type == "String") $type_color = "<span style='color:green'>";
        elseif($type == "Integer") $type_color = "<span style='color:red'>";
        elseif($type == "Double"){ $type_color = "<span style='color:#0099c5'>"; $type = "Float"; }
        elseif($type == "Boolean") $type_color = "<span style='color:#92008d'>";
        elseif($type == "NULL") $type_color = "<span style='color:black'>";

        if(is_array($avar))
        {
$count = count($avar);
            echo "$indent" . ($var_name ? "$var_name => ":"") . "<span style='color:#a2a2a2'>$type ($count)</span><br>$indent(<br>";
$keys = array_keys($avar);
            foreach($keys as $name)
            {
$value = &$avar[$name];
do_dump($value, "['$name']", $indent.$do_dump_indent, $reference);
            }
            echo "$indent)<br>";
        }
        elseif(is_object($avar))
        {
            echo "$indent$var_name <span style='color:#a2a2a2'>$type</span><br>$indent(<br>";
            foreach($avar as $name=>$value) do_dump($value, "$name", $indent.$do_dump_indent, $reference);
            echo "$indent)<br>";
        }
        elseif(is_int($avar)) echo "$indent$var_name = <span style='color:#a2a2a2'>$type(".strlen($avar).")</span> $type_color$avar</span><br>";
        elseif(is_string($avar)) echo "$indent$var_name = <span style='color:#a2a2a2'>$type(".strlen($avar).")</span> $type_color\"$avar\"</span><br>";
        elseif(is_float($avar)) echo "$indent$var_name = <span style='color:#a2a2a2'>$type(".strlen($avar).")</span> $type_color$avar</span><br>";
        elseif(is_bool($avar)) echo "$indent$var_name = <span style='color:#a2a2a2'>$type(".strlen($avar).")</span> $type_color".($avar == 1 ? "TRUE":"FALSE")."</span><br>";
        elseif(is_null($avar)) echo "$indent$var_name = <span style='color:#a2a2a2'>$type(".strlen($avar).")</span> {$type_color}NULL</span><br>";
        else echo "$indent$var_name = <span style='color:#a2a2a2'>$type(".strlen($avar).")</span> $avar<br>";

$var = $var[$keyvar];
    }
}
?>

down

Anonymous ¶

8 years ago

Be careful this outputs to stdout stream (1) instead of the proper stderr stream (2).

down

php at mikeboers dot com ¶

17 years ago

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!

down

david at exposito dot mobi ¶

15 years ago

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

down

kobrasrealm at gmail dot com ¶

13 years ago

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.

down

vladimir at pixeltomorrow dot com ¶

17 years ago

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

down

-1

fabien dot villepinte at gmail dot com ¶

5 years ago

It's important to note that the output depends on the precision directive.
<?php
var_dump(10000000000000.5); // float(10000000000000)
ini_set('precision',-1);
var_dump(10000000000000.5); // float(10000000000000.5)
?>

down

-3

divinity76 at gmail dot com ¶

13 years ago

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 )

down

-3

jonbarnett at gmail dot com ¶

18 years ago

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); 
/* dumps all of $brother's properties, including "sister", which dumps all of $sister's properties, including "brother", etc. */
?>

＋添加备注

官方地址：https://www.php.net/manual/en/function.var-dump.php

有任何技术问题请点击这里网站运营推广招聘

IT PHP 编程语言开发编程 Linux 科技 Elasticsearch HTML/CSS/XML 面试数据库网络 JAVA NoSQL C/C++ Golang 操作系统 Git 算法正则表达式 Redis 互联网 MySql 软件运维 JavaScript 国际架构设计 Mac OS Excel TCP/IP Windows Oracle Socket Vim VR MongoDB 运营 Python MemCache 商业硬件电子娱乐设计摄影 nginx WordPress 游戏 HTTP 团建数码电器 Docker

php7.3 使用 PDO_DM 扩展连接 DM8 中文乱码 PhpStorm中PHP注释的规范指南使用PHPWord将docx文件转换为html格式 docker-compose启动nginx与php-fpm laravel查看orm生成的sql PHPStorm ESC 会退出命令行 composer install参数 laravel orm中DB::insert方法导致内存泄漏的问题解决方法 php7 安装fileinfo扩展 adodb手册 ADORecordSet对象常用的php ADODB使用方法集锦 ADOConnection 公用函数利用php soap实现web service adodb连接mysql多个数据库的问题 mysql面试题 PHP注释规范 [PHP] inet_pton/inet_ntop IP地址转换函数 php上周一、本周一、下周一日期 PHP7添加redis扩展

略微加速

PHP官方手册 - 互联网笔记

var_dump

说明

参数

返回值

示例

参见

发现了问题？

用户贡献的备注 16 notes