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  • var_dump()

    (PHP 4, PHP 5, PHP 7)

    打印变量的相关信息

    说明

    var_dump(mixed $expression[,mixed$...]): 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 #1var_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() 以易于理解的格式打印变量。
    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
    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 $content;
    }
    ?>
    Fairly simple functions, but they're infinitely helpful (I use var_dump_pre() almost exclusively now).
    I post a new var_dump function with colors and collapse features. It can also adapt to terminal output if you execute it from there. No need to wrap it in a pre tag to get it to work in browsers. 
    <?php
    function dump_debug($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);
    }
    ?>
    
    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)
    ?>
    
    <?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>";
    }
    ?>
    
    var_dump(get_defined_vars());
    will dump all defined variables to the browser.
    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>';
    ?>
    
    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.
    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];
      }
    }
    ?>
    
    Note that var_dump reset()'s array internal pointer!
    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!
    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 )
    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
    Be careful this outputs to stdout stream (1) instead of the proper stderr stream (2).
    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
    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. */
    ?>
    

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