Last updated: Fri, 27 Jun 2008

Variáveis

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Introdução

As variáveis no PHP são representadas por um cifrão ($) seguido pelo nome da variável. Os nomes de variável no PHP fazem distinção entre maiúsculas e minúsculas.

Os nomes de variável seguem as mesmas regras como outros rótulos no PHP. Um nome de variável válido se inicia com uma letra ou sublinhado, seguido de qualquer número de letras, algarismos ou sublinhados. Em uma expressão regular isto poderia ser representado desta forma: '[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*'

Nota: Para nosso propósito, as letras a-z, A-Z e os caracteres ASCII de 127 a 255 (0x7f-0xff).

Nota: $this é uma variável especial que não pode ser atribuída.

Dica

Veja também o Guia de nomenclatura em espaço de usuário.

Para informação sobre funções relacionadas a variáveis, veja a Referência de funções para variáveis.


<?php
$var = 'Bob';
$Var = 'Joe';
echo "$var, $Var";      // exibe "Bob, Joe"

$4site = 'not yet';     // inválido; começa com um número
$_4site = 'not yet';    // válido; começa com um sublinhado
$täyte = 'mansikka';    // válido; 'ä' é um caracter ASCII (extendido) 228
?>

Por padrão, as variáveis são sempre atribuídas por valor. Isto significa que quando você atribui uma expressão a uma variável, o valor da expressão original é copiado integralmente para a variável de destino. Isto significa também que, após atribuir o valor de uma variável a outra, a alteração de uma destas variáveis não afetará a outra. Para maiores informações sobre este tipo de atribuição, veja o capítulo em Expressões.

O PHP oferece um outro meio de atribuir valores a variáveis: atribuição por referência. Isto significa que a nova variável simplesmente referencia (em outras palavras, "torna-se um apelido para" ou "aponta para") a variável original. Alterações na nova variável afetam a original e vice versa.

Para atribuir por referência, simplesmente adicione um e-comercial (&) na frente do nome da variável que estiver sendo atribuída (variável de origem) Por exemplo, o trecho de código abaixo imprime 'My name is Bob' duas vezes:


<?php
$foo = 'Bob';              // Atribui o valor 'Bob' a variável $foo
$bar = &$foo;              // Referecia $foo através de $bar.
$bar = "My name is $bar";  // Altera $bar...
echo $bar;
echo $foo;                 // $foo é alterada também.
?>

Uma observação importante a se fazer: somente variáveis nomeadas podem ser atribuídas por referência.


<?php
$foo = 25;
$bar = &$foo;      // Esta atribuição é válida.
$bar = &(24 * 7);  // Inválido; referencia uma expressão sem nome.

function test()
{
   return 25;
}

$bar = &test();    // Inválido.
?>

Não é necessário variáveis inicializadas no PHP, contudo é uma ótima prática. Variáveis não inicializadas tem um valor padrão do tipo dela - FALSE, zero, string vazia ou um array vazio.

Exemplo #1 Valores padrões de variáveis não inicializadas


<?php
echo ($unset_bool ? "true" : "false"); // false
$unset_int += 25; // 0 + 25 => 25
echo $unset_string . "abc"; // "" . "abc" => "abc"
$unset_array[3] = "def"; // array() + array(3 => "def") => array(3 => "def")
?>

Confiar no valor padrão de uma variável não inicializada é problemático no caso de incluir um arquivo em outro que usa variável com mesmo nome. E também um principal risco de segurança com register_globals estando on. Erros E_NOTICE são emitidos no caso de ter variáveis não inicializadas, contudo não no caso de adicionar elementos para um array não inicializado. O construtor da linguagem isset() pode ser usado para detectar se uma variável não foi inicializada.

Variáveis Pré-definidas

Manipulação de tipos

Last updated: Fri, 27 Jun 2008

add a note User Contributed Notes
Variáveis

taliesin at gmail dot com
24-May-2008 03:14


or you could change the order of the if



function var_name(&$var, $scope=0)

{

    if (($old = $var) &&  (($var = $old) || true) && ($key = array_search($var = 'unique'.rand().'value', !$scope ? $GLOBALS : $scope))) return $key;

}

ned at wgtech dot com
22-May-2008 12:07


The function given in lower posts:



function var_name(&$var, $scope=0)

{

    if (($old = $var) && ($key = array_search($var = 'unique'.rand().'value', !$scope ? $GLOBALS : $scope)) && (($var = $old) || true)) return $key;

}



has a nasty problem. If array_search fails the (($var=$old)||true) never gets evaluated, and rightly so, permanently changing the value of $var to 'unique#####value'.



How to fail the function:



$z=1;

var_name($z,array(1));



Easily fixed by adding an else:



function var_name(&$var, $scope=false)

{

    if ((($old=$var)||true)&&($key = array_search($var = 'unique'.rand().'value', !$scope ? $GLOBALS : $scope)) && (($var = $old) || true)) return $key;

    else $var=$old;return false;

}



All better.

john dot t dot gold at gmail dot com
20-May-2008 10:03


To list all Variables for debug purposes use this:



<?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>';

?>

(rot13) yrvsrevx [at] jro [dot] qr
15-Feb-2008 08:00


err, the "($old = $var)" could also evaluate to false. Adding a "|| true" would make this overall to crude, I guess. It's better to leave it out of the expression.

(rot13) yrvsrevx [at] jro [dot] qr
15-Feb-2008 05:22


@cgorbit: This does not work, because "=" has a lower operator precedence than "||". The expression "($var = $old || true)" assigns true to $var. I corrected this and further shortened the function by putting "$old = $var" into the expression, too. :)

Note the parentheses that are necessary because of the operator precedence of "=" and "&&".



function var_name(&$var, $scope=0)

{

    if (($old = $var) && ($key = array_search($var = 'unique'.rand().'value', !$scope ? $GLOBALS : $scope)) && (($var = $old) || true)) return $key;

}

cgorbit
05-Jan-2008 04:34


<?php

function var_name(&$var, $scope=0)

{

    $old = $var;

    if (($key = array_search($var = 'unique'.rand().'value', !$scope ? $GLOBALS : $scope)) && ($var = $old || true)) return $key;  

}

?>



Because $var may casts to false

alexandre at nospam dot gaigalas dot net
06-Jul-2007 10:13


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 09:48


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 03:10


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);

}



?>

whoami
28-Dec-2006 11:14


what is so simple and flexible about these variable..? They're all the same thing -.-"

$var = whatever;



in fact is more complicated than:



String HelloWorld = hello;

giunta dot gaetano at sea-aeroportimilano dot it
04-Aug-2006 02:44


With php 5.1.4 (and maybe earlier?) take care about not using $this as a variable name, even when in the global scope or inside a plain function: the engine will prevent assigning any value to it...

molnaromatic at gmail dot com
20-May-2006 06:44


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

warhog at warhog dot net
28-Dec-2005 12:11


> Variable names follow the same rules as other labels in PHP. A valid variable name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: '[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*'



..is not quite true. You can, in fact, only declare variables having a name like this if you use the syntax <?php $varname = "naks naks"; ?>.. but in fact a variable can have moreless any name that is a string... e.g. if you look at an array you can have

<?php

$arr[''];

$arr['8'];

$arr['-my-element-is-so-pretty-useless-'];

?>

.. by accessing the variables-namespace via {} you can have the same functinalities for all variables, e.g.



<?php ${''} = "my empty variable"; ?>



is a valid expression and the variable having the empty string as name will have the value "my empty variable".



read the chapter on "variable variables" for further information.

Mike at ImmortalSoFar dot com
25-Nov-2005 03:03


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 02:25


When using variable variables this is invalid:



$my_variable_{$type}_name = true;



to get around this do something like:



$n="my_variable_{$type}_name";

${$n} = true;



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

ludvig dot ericson at gmail dot com
13-Oct-2005 05:33


On the previous note:



This is due to how evaluation works. PHP will think of it as:



$a = whatever $b = $c is

$b = whatever $c = 1 is



... because an expression is equal to what it returns.



Therefore $c = 1 returns 1, making $b = $c same as $b = 1, which makes $b 1, which makes $a be $b, which is 1.



$a = ($b = $c = 1) + 2;

Will have $a be 3 while $b and $c is 1.



Hope that clears something up.

Chris Hester
31-Aug-2005 06:09


Variables can also be assigned together.



<?php

$a = $b = $c = 1;

echo $a.$b.$c;

?>



This outputs 111.

Mike Fotes
09-Jul-2005 12:46


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 02:06


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).

user at host dot network
01-May-2005 06:17


pay attention using spaces, dots and parenthesis in case kinda like..

$var=($number>0)?1.'parse error':0.'here too';

the correct form is..

$var=($number>0)?1 .'parse error':0 .'here too';

or

$var=($number>0)?(1).'parse error':(0).'here too';

or

$var = ($number > 0) ? 1 . 'parse error' : 0 . 'here too';

etc..

i think that's why the parser read 1. and 0. like decimal numbers not correctly written, point of fact

$var=$number>0?1.0.'parse error':0.0.'here too';

seems to work correctly..

david at rayninfo dot co dot uk
25-Apr-2005 05:01


When constructing strings from text and variables you can use curly braces to "demarcate" variables from any surrounding text where, for whatever reason, you cannot use a space eg:



$str="Hi my name is ${bold}$name bla-bla";



which AFAIK is the same as 



$str="Hi my name is {$bold}$name bla-bla";



zzapper

mike at go dot online dot pt
07-Apr-2005 10:18


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
14-Feb-2005 05:42


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

?>

jospape at hotmail dot com
05-Feb-2005 12:45


$id = 2;

$cube_2 = "Test";



echo ${cube_.$id};



// will output: Test

ringo78 at xs4all dot nl
14-Jan-2005 01:27


<?

// 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 04:02


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



<?



$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 11:58


<?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 surrealwebs dot com
09-Mar-2004 01:31


OK how about a practicle use for this:



You have a session variable such as:

$_SESSION["foo"] = "bar"

and you want to reference it to change it alot throughout the program instaed of typing the whole thing over and over just type this:



$sess =& $_SESSION

$sess['foo'] = bar;



echo $sess['foo'] // returns bar

echo $_SESSION["foo"] // also returns bar

just saves alot of time in the long run



also try $get = $HTTP_GET_VARS

or $post = $HTTP_POST_VARS

webmaster at daersys dot net
20-Jan-2004 09:15


In reference to "remco at clickbizz dot nl"'s note I would like to add that you don't necessarily have to escape the dollar-sign before a variable if you want to output it's 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
14-Jan-2003 07:37


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



eg:



$error_msg = &$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

add a note

Variáveis Pré-definidas

Manipulação de tipos

Last updated: Fri, 27 Jun 2008