extract
(PHP 4, PHP 5, PHP 7, PHP 8)
extract — 配列からシンボルテーブルに変数をインポートする
パラメータ
array
-
この関数は連想配列
var_array
を引数とし、そのキーを変数名、値を変数の値として処理します。 各キー/値の組に関して、flags
およびprefix
パラメータに基づき、 現在のシンボルテーブルに変数を一つ作成します。連想配列を使用する必要があります。
EXTR_PREFIX_ALL
またはEXTR_PREFIX_INVALID
を使用しない限り、 数値添字の配列には結果は出力されません。 flags
-
無効または数値キーおよび衝突に関する対処法は、
flags
で定義されます。 これは以下の値のどれかとなります。EXTR_OVERWRITE
- 衝突があった場合、存在する変数が上書きされます。
EXTR_SKIP
- 衝突があった場合、存在する変数は上書きされません。
EXTR_PREFIX_SAME
-
衝突があった場合、
prefix
を前につけた新しい変数となります。 EXTR_PREFIX_ALL
-
全ての変数の前に
prefix
を付けます。 EXTR_PREFIX_INVALID
-
無効または数値の変数名のみに接頭辞
prefix
を付けます。 EXTR_IF_EXISTS
- 現在のシンボルテーブルに既に存在する場合にのみ上書きします。 例えば $_REQUEST からあなたが定義した変数のみを展開し 有効な変数としたいような場合に有用です。
EXTR_PREFIX_IF_EXISTS
- 同じ変数だが接頭辞をつけていないバージョンの変数が 現在のシンボルテーブルに存在する場合にのみ 変数を生成します。
EXTR_REFS
-
変数を参照として展開します。
これはインポート済みの変数が、
array
パラメータの値に常に参照付けられることを意味します。 このフラグを単独で使用するか、 あるいはflags
と和算することにより、 他のフラグとそれを組み合わせることができます。
flags
が指定されない場合、EXTR_OVERWRITE
とみなされます。 prefix
-
prefix
は、flags
がEXTR_PREFIX_SAME
、EXTR_PREFIX_ALL
、EXTR_PREFIX_INVALID
あるいはEXTR_PREFIX_IF_EXISTS
の場合にのみ必要であることに注意してください。 接頭辞を付けた変数名が有効な変数名でない場合、 この変数はシンボルテーブルにインポートされません。接頭辞は、 アンダースコア文字で配列のキーから自動的に分割されます。
戻り値
シンボルテーブルにインポートした変数の数を返します。
例
例1 extract() の例
extract の使用例としては、シンボルテーブルに wddx_deserialize() から返された連想配列を インポートすることが考えられます。
<?php
/* $var_array はwddx_deserializeから返された配列と仮定します */
$size = "large";
$var_array = array(
"color" => "blue",
"size" => "medium",
"shape" => "sphere"
);
extract($var_array, EXTR_PREFIX_SAME, "wddx");
echo "$color, $size, $shape, $wddx_size\n";
?>
上の例の出力は以下となります。
blue, large, sphere, medium
EXTR_PREFIX_SAME
を指定したため、$size
は上書きされず、$wddx_size が作成されます。
EXTR_SKIP
が指定された場合、$wddx_size は作成されません。
EXTR_OVERWRITE
の場合は、$size の値は "medium" となります。
EXTR_PREFIX_ALL
の場合は新規の変数
$wddx_color,
$wddx_size, $wddx_shape
が作成されます。
注意
extract() をユーザー入力
($_GET や $_FILES など)
のような信頼できないデータについて使用しないでください。
もし行う場合、
EXTR_SKIP
のような flags
の値が上書きされていないことを確認してください。そして
php.ini の
variables_order
で定義されたものと同じ順で展開すべきであることに留意してください。
User Contributed Notes 28 notes
They say "If the result is not a valid variable name, it is not imported into the symbol table."
What they should say is that if _any_ of the results have invalid names, _none_ of the variables get extracted.
Under 4.3.10 on Windows 2000, I was pulling some mySQL records, but needed to convert two fields into IP addresses:
<?
extract(mysql_fetch_assoc(mysql_query('SELECT * FROM foo')));
extract(mysql_fetch_assoc(mysql_query('SELECT INET_NTOA(bar) AS bar, INET_NTOA(baz) FROM foo')));
?>
I had forgotten the second AS modifier in the SQL query. Because it couldn't extract a variable called INET_NTOA(baz) into the symbol table, it didn't do either of them.
(BTW I don't normally stack functions up like that! Just to make a short example!)
It is possible to use this as a way to create public attributes for a class.
<?php
class Foo {
public function __construct ($array) {
extract($array, EXTR_REFS);
foreach ($array as $key => $value) {
$this->$key = $$key;
// Do: $this->key = $key; if $key is not a string.
}
}
}
$array = array(
'valueOne' => 'Test Value 1',
'valueTwo' => 'Test Value 2',
'valueThree' => 'Test Value 3'
);
$foo = new Foo($array);
// Works
echo $foo->valueOne; // Test Value 1
echo $foo->valueTwo; // Test Value 2
// Does not work!
echo $foo::$valueOne; // Fatal error: Access to undeclared static property: Test::$valueOne
?>
Sometimes you may want to extract only a named subset of the key/value pairs in an array. This keeps things more orderly and could prevent an unrelated variable from getting clobbered from an errant key. For example,
$things = 'unsaid';
$REQUEST = array(He=>This, said=>1, my=>is, info=>2, had=>a,
very=>3, important=>test, things=>4);
$aVarToExtract = array(my, important, info);
extract (array_intersect_key ($REQUEST, array_flip($aVarToExtract)));
will extract
$my = 'is';
$important = 'test';
$info = 2;
but will leave certain
$things = 'unsaid'
Csaba Gabor from Vienna
NB. Of course the composite request coming in from a web page is in $_REQUEST.
I have made some tests to compare the speed of next constructions:
<?php
extract($ARRAY);
// vs.
foreach($ARRAY as $key=>$value)
$$key = $value;
?>
Surprisingly for me extract is 20%-80% slower then foreach construction. I don't really understand why, but it's so.
When extracting from a row after a database query using for example:
$row = mysql_fetch_array($result, MYSQL_ASSOC)
extract($row);
I find that the resultant variables may not match the variable type in the database. In particular I have found integers in the database may gettype() to string on the extracted variable.
Following up on ktwombley at gmail dot com's post:
Presumably one easy way of dealing with this security issue is to use the EXTR_IF_EXISTS flag and make sure
a) your define acceptable input variables beforehand (i.e. as empty variables)
b) Sanitise any user input to avoid unacceptable variable content.
If you do these two things, then I'm not sure I see the difference between extract($_REQUEST,EXTR_IF_EXISTS); and assigning each of the variables by hand.
I'm not talking here about the idea of storing the variables in a database, just the immediately necessary steps to allow you to use extract on REQUEST arrays with relative safety.
[New Version]
Example Usage:
<?php
$_GET['A']['a'] = ' CORRECT(including some spaces) ';
$_GET['A']['b'] = ' CORRECT(including some spaces) ';
$_GET['A']['c'] = "Invalid UTF-8 sequence: \xe3\xe3\xe3";
$_GET['A']['d']['invalid_structure'] = 'INVALID';
$_GET['B']['a'] = ' CORRECT(including some spaces) ';
$_GET['B']['b'] = "Invalid UTF-8 sequence: \xe3\xe3\xe3";
$_GET['B']['c']['invalid_structure'] = 'INVALID';
$_GET['B']["Invalid UTF-8 sequence: \xe3\xe3\xe3"] = 'INVALID';
$_GET['C']['a'] = ' CORRECT(including some spaces) ';
$_GET['C']['b'] = "Invalid UTF-8 sequence: \xe3\xe3\xe3";
$_GET['C']['c']['invalid_structure'] = 'INVALID';
$_GET['C']["Invalid UTF-8 sequence: \xe3\xe3\xe3"] = 'INVALID';
$_GET['unneeded_item'] = 'UNNEEDED';
var_dump(filter_struct_utf8(INPUT_GET, array(
'A' => array(
'a' => '',
'b' => FILTER_STRUCT_TRIM,
'c' => '',
'd' => '',
),
'B' => FILTER_STRUCT_FORCE_ARRAY,
'C' => FILTER_STRUCT_FORCE_ARRAY | FILTER_STRUCT_TRIM,
)));
?>
Example Result:
array(3) {
["A"]=>
array(4) {
["a"]=>
string(36) " CORRECT(including some spaces) "
["b"]=>
string(30) "CORRECT(including some spaces)"
["c"]=>
string(0) ""
["d"]=>
string(0) ""
}
["B"]=>
array(3) {
["a"]=>
string(36) " CORRECT(including some spaces) "
["b"]=>
string(0) ""
["c"]=>
string(0) ""
}
["C"]=>
array(3) {
["a"]=>
string(30) "CORRECT(including some spaces)"
["b"]=>
string(0) ""
["c"]=>
string(0) ""
}
}
If an object is typecasted into an array and "extracted",only the public properties will be accessible.Methods are of course omitted.
<?php
class Test{
public $name = '';
protected $age = 10;
public $status = 'disabled';
private $isTrue = false;
public function __construct()
{
$this->name = 'Amolo';
$this->status = 'active';
}
public function getName()
{
return $this->name;
}
public function getAge()
{
return $this->age;
}
public function getStatus()
{
return $this->status;
}
}
$obj = (array) new Test();
var_dump($obj);
/* array(4) { ["name"]=> string(5) "Amolo" ["*age"]=> int(10) ["status"]=> string(6) "active" ["TestisTrue"]=> bool(false) } */
extract((array)new Test());
echo $name; //Amolo
echo $status; //active
echo $age;//Notice: Undefined variable: age
echo $isTrue;//Notice: Undefined variable: isTrue
Using extract's return parameter can lead to unintended results, particularly with EXTR_REFS:
<?php
$my_data = [
'count' => 15,
'name' => 'foo',
];
$count = extract( $my_data, EXTR_REFS );
echo $my_data['count']; // 2, not 15.
You can't extract a numeric indexed array(e.g. non-assoc array).
<?php
$a = array(
1,
2
);
extract($a);
var_dump(${1});
?>
result:
PHP Notice: Undefined variable: 1 in /Users/Lutashi/t.php on line 7
Notice: Undefined variable: 1 in /Users/Lutashi/t.php on line 7
NULL
We can use extract () function for Template Engine:
<?php
#Template.php
class Template
{
protected $viewVars;
public function renderPage($tpl)
{
ob_start();
extract($this->viewVars, EXTR_SKIP);
include $tpl;
return ob_end_flush();
}
public function assign($arr)
{
foreach ($arr as $key => $value) {
$this->viewVars[$key] = $value;
}
return $this;
}
}
$template = new Template();
$template->assign(
[ 'pageHeader' => 'Page Header', 'content' => 'This is the content page']
);
$template->renderPage('tpl.php');
#tpl.php
<h1><?= $pageHeader; ?></h1>
<p><?= $content ;?></p>
Output:
Page Header
This is the content page
[New Version]
This function is very useful for filtering complicated array structure.
Also, Some integer bitmasks and invalid UTF-8 sequence detection are available.
Code:
<?php
/**
* @param integer $type Constant like INPUT_XXX.
* @param array $default Default structure of the specified super global var.
* Following bitmasks are available:
* + FILTER_STRUCT_FORCE_ARRAY - Force 1 dimensional array.
* + FILTER_STRUCT_TRIM - Trim by ASCII control chars.
* + FILTER_STRUCT_FULL_TRIM - Trim by ASCII control chars,
* full-width and no-break space.
* @return array The value of the filtered super global var.
*/
define('FILTER_STRUCT_FORCE_ARRAY', 1);
define('FILTER_STRUCT_TRIM', 2);
define('FILTER_STRUCT_FULL_TRIM', 4);
function filter_struct_utf8($type, array $default) {
static $func = __FUNCTION__;
static $trim = "[\\x0-\x20\x7f]";
static $ftrim = "[\\x0-\x20\x7f\xc2\xa0\xe3\x80\x80]";
static $recursive_static = false;
if (!$recursive = $recursive_static) {
$types = array(
INPUT_GET => $_GET,
INPUT_POST => $_POST,
INPUT_COOKIE => $_COOKIE,
INPUT_REQUEST => $_REQUEST,
);
if (!isset($types[(int)$type])) {
throw new LogicException('unknown super global var type');
}
$var = $types[(int)$type];
$recursive_static = true;
} else {
$var = $type;
}
$ret = array();
foreach ($default as $key => $value) {
if ($is_int = is_int($value)) {
if (!($value | (
FILTER_STRUCT_FORCE_ARRAY |
FILTER_STRUCT_FULL_TRIM |
FILTER_STRUCT_TRIM
))) {
$recursive_static = false;
throw new LogicException('unknown bitmask');
}
if ($value & FILTER_STRUCT_FORCE_ARRAY) {
$tmp = array();
if (isset($var[$key])) {
foreach ((array)$var[$key] as $k => $v) {
if (!preg_match('//u', $k)){
continue;
}
$value &= FILTER_STRUCT_FULL_TRIM | FILTER_STRUCT_TRIM;
$tmp += array($k => $value ? $value : '');
}
}
$value = $tmp;
}
}
if ($isset = isset($var[$key]) and is_array($value)) {
$ret[$key] = $func($var[$key], $value);
} elseif (!$isset || is_array($var[$key])) {
$ret[$key] = null;
} elseif ($is_int && $value & FILTER_STRUCT_FULL_TRIM) {
$ret[$key] = preg_replace("/\A{$ftrim}++|{$ftrim}++\z/u", '', $var[$key]);
} elseif ($is_int && $value & FILTER_STRUCT_TRIM) {
$ret[$key] = preg_replace("/\A{$trim}++|{$trim}++\z/u", '', $var[$key]);
} else {
$ret[$key] = preg_replace('//u', '', $var[$key]);
}
if ($ret[$key] === null) {
$ret[$key] = $is_int ? '' : $value;
}
}
if (!$recursive) {
$recursive_static = false;
}
return $ret;
}
?>
This function provides exactly the same functionality as extract except that a parameter was added defining the extract target.
This function can be used if your PHP installation does not support the required Flags or more important if you would like to extract arrays to another destination as to $GLOBALS, i.e. other arrays or objects.
The only difference to extract is that extract_to moves the array pointer of $arr to the end as $arr is passed by reference to support the EXTR_REFS flag.
<?php
if( !defined('EXTR_PREFIX_ALL') ) define('EXTR_PREFIX_ALL', 3);
if( !defined('EXTR_PREFIX_INVALID') ) define('EXTR_PREFIX_INVALID', 4);
if( !defined('EXTR_IF_EXISTS') ) define('EXTR_IF_EXISTS', 5);
if( !defined('EXTR_PREFIX_IF_EXISTS') ) define('EXTR_PREFIX_IF_EXISTS', 6);
if( !defined('EXTR_REFS') ) define('EXTR_REFS', 256);
function extract_to( &$arr, &$to, $type=EXTR_OVERWRITE, $prefix=false ){
if( !is_array( $arr ) ) return trigger_error("extract_to(): First argument should be an array", E_USER_WARNING );
if( is_array( $to ) ) $t=0;
else if( is_object( $to ) ) $t=1;
else return trigger_error("extract_to(): Second argument should be an array or object", E_USER_WARNING );
if( $type==EXTR_PREFIX_SAME || $type==EXTR_PREFIX_ALL || $type==EXTR_PREFIX_INVALID || $type==EXTR_PREFIX_IF_EXISTS )
if( $prefix===false ) return trigger_error("extract_to(): Prefix expected to be specified", E_USER_WARNING );
else $prefix .= '_';
$i=0;
foreach( $arr as $key=>$val ){
$nkey = $key;
$isset = $t==1 ? isset( $to[$key] ) : isset( $to->$key );
if( ( $type==EXTR_SKIP && $isset )
|| ( $type==EXTR_IF_EXISTS && !$isset ) )
continue;
else if( ( $type==EXTR_PREFIX_SAME && $isset )
|| ( $type==EXTR_PREFIX_ALL )
|| ( $type==EXTR_PREFIX_INVALID && !preg_match( '#^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$#', $key ) ) )
$nkey = $prefix.$key;
else if( $type==EXTR_PREFIX_IF_EXISTS )
if( $isset ) $nkey = $prefix.$key;
else continue;
if( !preg_match( '#^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$#', $nkey ) ) continue;
if( $t==1 )
if( $type & EXTR_REFS ) $to->$nkey = &$arr[$key];
else $to->$nkey = $val;
else
if( $type & EXTR_REFS ) $to[$nkey] = &$arr[$key];
else $to[$nkey] = $val;
$i++;
}
return $i;
}
// e.g.:
extract_to( $myarray, $myobject, EXTR_IF_EXISTS );
?>
Re: anon at anon dot org, about extract() and null values
Personally I've found use extracting multiple resultsets from db where the latter would overwrite the previous when a variable is not null ( and optionally if its not >0 )
It would be useful if $extract_type was extended on top of these two:
EXTR_OVERWRITE
EXTR_SKIP
with something like this:
EXTR_OVERWRITE_NULL
- If there is a collision, overwrite the existing variable if it is null
EXTR_OVERWRITE_0
- Same thing but == 0 or null
EXTR_SKIP_NULL
- If there is a collision, skip the new variable if the existing is not null
EXTR_SKIP_0
- Same thing but == 0 or null
Those ought to cover a few good cases that aren't covered now.
Note that extract() will only create or overwrite variables in the current scope, so
<?
function test(){
$a=Array('b'=>1,'c'=>2);
extract($a);
}
test();
exit("$b");
?>
will produce no output, whereas
<?
function test(){
global $b;
$a=Array('b'=>1,'c'=>2);
extract($a);
}
test();
exit("$b");
?>
will output 1.
Dan O'Donnell's suggestion needs a third requirement to work as described:
c) No other variables are defined - especially variables that contain potentially sensitive information.
Without that condition the difference between extract() and assigning variables by hand (and the resulting security implications) should be obvious.
The only valid security step there is (b) - but you should be doing that anyway.
And if you want with PHP 5 an easy way to extract $V by reference, try this :
<?php
foreach ($V as $k => &$v) {
$$k =& $v;
}
?>
It can be used to create special kind of "free args" functions that let you choose when you call them the way you send variables, and which ones. They are moreover very fast to call thanks to references :
<?php
function free_args (&$V) {
foreach ($V as $k => &$v) {
$$k =& $v;
}
unset ($k); unset ($v); unset ($V);
// be careful that if you need to extract $k, $v or $V variables you should find other names for them in the lines above (ie. $__k, $__v and $__V)
}
$huge_text = '...';
$a = array ('arg1' => 'val1', 'arg2' => &$huge_text); // in this call, only $arg2 will be a true reference in the function
free_args ($a);
?>
Be warned that you can't write : "<?php free_args (array ('arg1' => 'val1')); ?>" because the array can't be referenced by the function, as it's not yet created when the function starts.
It's really easy to open gaping security holes using extract() on $_REQUEST, $_GET, etc. You have to be really sure of what you're doing, and use the proper flags on extract() to avoid clobbering important variables.
For instance, the submission by kake26 at gmail dot com will not only perfectly emulate register globals (that's bad), but it'll store it in a database and recall the same variables every time the script runs (essentially allowing an attacker to attack your script every time it runs via one attack). Oops!
To fix it, you'd have to get creative with flags. Maybe you could use EXTR_PREFIX_ALL instead of EXTR_OVERWRITE, for example. Of course, you should also sanitize the form elements to ensure there's no php code in them, and also to make sure any very important variables aren't in the form data. (like the classic $is_admin = true attack)
As shown in the example, if your 'prefix' is used, a single underscore is added to the name of the extracted variable. Meaning, a prefix of 'p' becomes a prefix of 'p_', so 'blarg' prefixed would be 'p_blarg'.
If you're not sure what variables you've created through extraction, you can call get_defined_vars() to see all defined variables in the current scope.
To make this perfectly clear (hopefully), an underscore is always added when the string is prefixed.
extract(array("color" => "blue"),EXTR_PREFIX_ALL,'');// note: prefix is empty
is the same as
$color='_blue';
I would draw your attention to the user note at the very end of this page regarding PREFIXES. The user points out that php adds a '_' to your prefixes.
A warning about extract() and null values.
This might be an actual Zend2 Engine bug, but it's bad programming practice, so I'm sharing it here instead.
I often work in envrionments where E_STRICT (which would prevent errors like this) isn't on, and I don't have access to change it. I also use a very simple template class that in a nutshell works like this:
$t = new Template('somefile.php');
$t->title = $title;
$t->body = $body;
$t->display();
display() more or less looks like this:
function display(){
extract(get_object_vars($this),EXTR_REFS);
ob_start(); include $this->templateFileName;
return ob_get_clean();
}
If any of the assigned values are null (let's say that in this case $title wasn't initialized above) it causes the engine to do all sorts of incredibly whacky stuff like certifiably lose track of variables in an incredibly inconsistent way. I traced the problem down to the fact that it's using the EXTR_REFS flag. I assume that in PHP's internal variable storage or reference counting mechanism, that trying to extract null references makes it lose track or count of something or rather.
In a nutshell, if you start getting wierd behavior when using extract() make sure that the array or object you are trying to get variables out of doesn't contain null keys or values!
I use XDebug with NetbeansIDE to for analyzing and developing PHP Code. When debugging an extract statement no new variables appeared in the variable's list. Although all variables created by extract could be examined by explicit watch items and single variables appeared as soon as an PHP script makes use of them I am not sure weather it is a wrong configuration, a feature or a bug in XDebug.