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Variables

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Language Reference
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PHP Manual
PHP手册 - N: Variables

User contributed notes:

james at custom-made-sites dot com (30-Sep-2010 12:55)

This script has been running around for a while and has add many additions and changes, however I noticed that if you run it and there is an object assigned to a variable it will fail with 'Object of Class 'XXXX' cannot be converted to string'
so I changed it a little to ignore objects within the script and display the variables only:

Btw, it has haelped me an ENOURMOUS amount over the years especially when keeping track of variables that are being sent through request and if session variables are alive

<?php

//this can be removed if you want to find out if you page has actually started a session, - this is sometimes a problem when relying on a session being started by an included/required file
if(!isset($_SESSION))
{
session_start();
}

//now begin the table
echo '<table border=1><tr> <th>variable</th> <th>value</th> </tr>';
foreach(get_defined_vars() as $key => $value)
{
//if the returned value is NOT an object...
    if (is_array ($value) && !is_object($key) && !is_object($value))
    {
        echo '<tr><td>$'.$key .'</td><td>';
        if ( sizeof($value)>0 )
        {
        echo '"<table border=1><tr> <th>key</th> <th>value</th> </tr>';
        foreach ($value as $skey => $svalue )
        {
 //and if these values are NOT an object...

    if ( !is_object($skey) && !is_object($svalue))
    {
            echo '<tr><td>[' . $skey .']</td><td>"'. $svalue .'"</td></tr>';
    }
        }
        echo '</table>"';
        }
             else
        {
            echo 'EMPTY';
        }
        echo '</td></tr>';
    }else

    {
            echo '<tr><td>[' . $key .']</td><td>"'. $value .'"</td></tr>';
    }
   
   
   
}

echo '</table>';
?>

justgook at gmail dot com (03-Aug-2010 09:38)

I found interstate solution to work with arrays

<?php
$vars['product']['price']=11;

$aa='product';
$bb='price';

echo $vars{$aa}{$bb};

//prints 11
?>

dimitrov dot adrian at gmail dot com (29-Jul-2010 02:52)

This is mine type casting lib, that is very useful for me.

<?php

function CAST_TO_INT($var, $min = FALSE, $max = FALSE)
{
    $var = is_int($var) ? $var : (int)(is_scalar($var) ? $var : 0);
    if ($min !== FALSE && $var < $min)
        return $min;
    elseif($max !== FALSE && $var > $max)
        return $max;
    return $var;
       
}

function CAST_TO_FLOAT($var, $min = FALSE, $max = FALSE)
{
    $var = is_float($var) ? $var : (float)(is_scalar($var) ? $var : 0);
    if ($min !== FALSE && $var < $min)
        return $min;
    elseif($max !== FALSE && $var > $max)
        return $max;
    return $var;
}

function CAST_TO_BOOL($var)
{
    return (bool)(is_bool($var) ? $var : is_scalar($var) ? $var : FALSE);
}

function CAST_TO_STRING($var, $length = FALSE)
{
    if ($length !== FALSE && is_int($length) && $length > 0)
        return substr(trim(is_string($var)
                    ? $var
                    : (is_scalar($var) ? $var : '')), 0, $length);

    return trim(
                is_string($var)
                ? $var
                : (is_scalar($var) ? $var : ''));
}

function CAST_TO_ARRAY($var)
{
    return is_array($var)
            ? $var
            : is_scalar($var) && $var
                ? array($var)
                : is_object($var) ? (array)$var : array();
}

function CAST_TO_OBJECT($var)
{
    return is_object($var)
            ? $var
            : is_scalar($var) && $var
                ? (object)$var
                : is_array($var) ? (object)$var : (object)NULL;
}

?>

Anonymous (20-Jul-2008 02:25)

[EDIT by danbrown AT php DOT net: The function provided by this author will give you all defined variables at runtime.  It was originally written by (john DOT t DOT gold AT gmail DOT com), but contained some errors that were corrected in subsequent posts by (ned AT wgtech DOT com) and (taliesin AT gmail DOT com).]

<?php

echo '<table border=1><tr> <th>variable</th> <th>value</th> </tr>';
foreach( get_defined_vars() as $key => $value)
{
    if (is_array ($value) )
    {
        echo '<tr><td>$'.$key .'</td><td>';
        if ( sizeof($value)>0 )
        {
        echo '"<table border=1><tr> <th>key</th> <th>value</th> </tr>';
        foreach ($value as $skey => $svalue)
        {
            echo '<tr><td>[' . $skey .']</td><td>"'. $svalue .'"</td></tr>';
        }
        echo '</table>"';
        }
             else
        {
            echo 'EMPTY';
        }
        echo '</td></tr>';
    }
    else
    {
            echo '<tr><td>$' . $key .'</td><td>"'. $value .'"</td></tr>';
    }
}
echo '</table>';
?>

alexandre at nospam dot gaigalas dot net (07-Jul-2007 05:13)

Here's a simple solution for retrieving the variable name, based on the lucas (http://www.php.net/manual/en/language.variables.php#49997) solution, but shorter, just two lines =)

<?php
function var_name(&$var, $scope=0)
{
    $old = $var;
    if (($key = array_search($var = 'unique'.rand().'value', !$scope ? $GLOBALS : $scope)) && $var = $old) return $key; 
}
?>

jsb17 at cornell dot edu (20-Feb-2007 04:48)

As an addendum to David's 10-Nov-2005 posting, remember that curly braces literally mean "evaluate what's inside the curly braces" so, you can squeeze the variable variable creation into one line, like this:

<?php
  ${"title_default_" . $title} = "selected";
?>

and then, for example:

<?php
  $title_select = <<<END
    <select name="title">
      <option>Select</option>
      <option $title_default_Mr  value="Mr">Mr</option>
      <option $title_default_Ms  value="Ms">Ms</option>
      <option $title_default_Mrs value="Mrs">Mrs</option>
      <option $title_default_Dr  value="Dr">Dr</option>
    </select>
END;
?>

code at slater dot fr (25-Jan-2007 10:10)

Here's a pair of functions to encode/decode any string to be a valid php and javascript variable name.

<?php

function label_encode($txt) {
 
  // add Z to the begining to avoid that the resulting
  // label is a javascript keyword or it starts with a
  // number
  $txt = 'Z'.$txt;
 
  // encode as urlencoded data
  $txt = rawurlencode($txt);
 
  // replace illegal characters
  $illegal = array('%', '-', '.');
  $ok = array('é', 'è', 'à');
  $txt = str_replace($illegal,$ok, $txt);
 
  return $txt;
}

function label_decode($txt) {
 
  // replace illegal characters
  $illegal = array('%', '-', '.');
  $ok = array('é', 'è', 'à');
  $txt = str_replace($ok, $illegal, $txt);
 
  // unencode
  $txt = rawurldecode($txt);
 
  // remove the leading Z and return
  return substr($txt,1);
}

?>

molnaromatic at gmail dot com (20-May-2006 01:44)

Simple sample and variables and html "templates":
The PHP code:
variables.php:
<?php
$SYSN["title"] = "This is Magic!";
$SYSN["HEADLINE"] = "Ez magyarul van"; // This is hungarian
$SYSN["FEAR"] = "Bell in my heart";
?>

index.php:
<?php
include("variables.php");
include("template.html");
?>

The template:
template.html

<html>
<head><title><?=$SYSN["title"]?></title></head>
<body>
<H1><?=$SYSN["HEADLINE"]?></H1>
<p><?=$SYSN["FEAR"]?></p>
</body>
</html>
This is simple, quick and very flexibile

Mike at ImmortalSoFar dot com (25-Nov-2005 10:03)

References and "return" can be flakey:

<?php
//  This only returns a copy, despite the dereferencing in the function definition
function &GetLogin ()
{
    return $_SESSION['Login'];
}

//  This gives a syntax error
function &GetLogin ()
{
    return &$_SESSION['Login'];
}

//  This works
function &GetLogin ()
{
    $ret = &$_SESSION['Login'];
    return $ret;
}
?>

david at removethisbit dot futuresbright dot com (10-Nov-2005 09:25)

When using variable variables this is invalid:

<?php
$my_variable_{$type}_name = true;
?>

to get around this do something like:

<?php
$n="my_variable_{$type}_name";
${$n} = true;
?>

(or $$n - I tend to use curly brackets out of habit as it helps t reduce bugs ...)

Chris Hester (31-Aug-2005 01:09)

Variables can also be assigned together.

<?php
$a = $b = $c = 1;
echo $a.$b.$c;
?>

This outputs 111.

Mike Fotes (09-Jul-2005 07:46)

In conditional assignment of variables, be careful because the strings may take over the value of the variable if you do something like this:

<?php
$condition = true;

// Outputs " <-- That should say test"
echo "test" . ($condition) ? " <-- That should say test" : "";
?>

You will need to enclose the conditional statement and assignments in parenthesis to have it work correctly:

<?php
$condition = true;

// Outputs "test <-- That should say test"
echo "test" . (($condition) ? " <-- That should say test " : "");
?>

josh at PraxisStudios dot com (17-May-2005 09:06)

As with echo, you can define a variable like this:

<?php

$text = <<<END

<table>
    <tr>
        <td>
             $outputdata
        </td>
     </tr>
</table>

END;

?>

The closing END; must be on a line by itself (no whitespace).

[EDIT by danbrown AT php DOT net: This note illustrates HEREDOC syntax.  For more information on this and similar features, please read the "Strings" section of the manual here: http://www.php.net/manual/en/language.types.string.php ]

mike at go dot online dot pt (07-Apr-2005 05:18)

In addition to what jospape at hotmail dot com and ringo78 at xs4all dot nl wrote, here's the sintax for arrays:

<?php
//considering 2 arrays
$foo1 = array ("a", "b", "c");
$foo2 = array ("d", "e", "f");

//and 2 variables that hold integers
$num = 1;
$cell = 2;

echo ${foo.$num}[$cell]; // outputs "c"

$num = 2;
$cell = 0;

echo ${foo.$num}[$cell]; // outputs "d"
?>

lucas dot karisny at linuxmail dot org (15-Feb-2005 12:42)

Here's a function to get the name of a given variable.  Explanation and examples below.

<?php
  function vname(&$var, $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;
    return $vname;
  }
?>

Explanation:

The problem with figuring out what value is what key in that variables scope is that several variables might have the same value.  To remedy this, the variable is passed by reference and its value is then modified to a random value to make sure there will be a unique match.  Then we loop through the scope the variable is contained in and when there is a match of our modified value, we can grab the correct key.

Examples:

1.  Use of a variable contained in the global scope (default):
<?php
  $my_global_variable = "My global string.";
  echo vname($my_global_variable); // Outputs:  my_global_variable
?>

2.  Use of a local variable:
<?php
  function my_local_func()
  {
    $my_local_variable = "My local string.";
    return vname($my_local_variable, get_defined_vars());
  }
  echo my_local_func(); // Outputs: my_local_variable
?>

3.  Use of an object property:
<?php
  class myclass
  {
    public function __constructor()
    {
      $this->my_object_property = "My object property  string.";
    }
  }
  $obj = new myclass;
  echo vname($obj->my_object_property, $obj); // Outputs: my_object_property
?>

ringo78 at xs4all dot nl (14-Jan-2005 08:27)

<?php
// I am beginning to like curly braces.
// I hope this helps for you work with them
$filename0="k";
$filename1="kl";
$filename2="klm";
 $i=0;
for ($varname = sprintf("filename%d",$i);   isset  ( ${$varname} ) ;   $varname = sprintf("filename%d", $i)  )  {
    echo "${$varname} <br>";
    $varname = sprintf("filename%d",$i);
    $i++;
}
?>

Carel Solomon (07-Jan-2005 11:02)

You can also construct a variable name by concatenating two different variables, such as:

<?php

$arg = "foo";
$val = "bar";

//${$arg$val} = "in valid";     // Invalid
${$arg . $val} = "working";

echo $foobar;     // "working";
//echo $arg$val;         // Invalid
//echo ${$arg$val};     // Invalid
echo ${$arg . $val};    // "working"

?>

Carel

raja shahed at christine nothdurfter dot com (25-May-2004 06:58)

<?php
error_reporting(E_ALL);

$name = "Christine_Nothdurfter";
// not Christine Nothdurfter
// you are not allowed to leave a space inside a variable name ;)
$$name = "'s students of Tyrolean language ";

print " $name{$$name}<br>";
print  "$name$Christine_Nothdurfter";
// same
?>

webmaster at daersys dot net (20-Jan-2004 04:15)

You don't necessarily have to escape the dollar-sign before a variable if you want to output its name.

You can use single quotes instead of double quotes, too.

For instance:

<?php
$var = "test";

echo "$var"; // Will output the string "test"

echo "\$var"; // Will output the string "$var"

echo '$var'; // Will do the exact same thing as the previous line
?>

Why?
Well, the reason for this is that the PHP Parser will not attempt to parse strings encapsulated in single quotes (as opposed to strings within double quotes) and therefore outputs exactly what it's being fed with :)

To output the value of a variable within a single-quote-encapsulated string you'll have to use something along the lines of the following code:

<?php
$var = 'test';
/*
Using single quotes here seeing as I don't need the parser to actually parse the content of this variable but merely treat it as an ordinary string
*/

echo '$var = "' . $var . '"';
/*
Will output:
$var = "test"
*/
?>

HTH
- Daerion

unleaded at nospam dot unleadedonline dot net (15-Jan-2003 02:37)

References are great if you want to point to a variable which you don't quite know the value yet ;)

eg:

<?php
$error_msg = &$messages['login_error']; // Create a reference

$messages['login_error'] = 'test'; // Then later on set the referenced value

echo $error_msg; // echo the 'referenced value'
?>

The output will be:

test