extract
(PHP 4, PHP 5)
extract — Импортировать переменные из массива в текущую символьную таблицу.
Описание
Эта функция используется для импорта переменных из массива в текущую символьную таблицу. Она берёт ассоциативный массив в качестве параметра var_array и трактует его ключи как имена переменных и значения как значения переменных. Для каждой пары ключ/значение будет создана переменная в текущей символьной таблице, согласно параметрам extract_type и prefix .
Замечание: Начиная с версии 4.0.5, эта функция возвращает количество извлечённых переменных.
Замечание: EXTR_IF_EXISTS и EXTR_PREFIX_IF_EXISTS были добавлены в версии 4.2.0.
Замечание: EXTR_REFS был добавлен в версии 4.3.0.
extract() проверяет каждый ключ на соответствие приемлемости в качестве имени переменной. Эта функция также обрабатывает коллизии имён, если ключ совпадает с именем переменной, уже существующей в текущей символьной таблице. Способ обработки неприемлемых/числовых ключей и коллизий имён устанавливает параметр extract_type . Он может принимать одно из следующих значений:
- EXTR_OVERWRITE
- Если переменная с таким именем существует, она будет переназначена.
- EXTR_SKIP
- Если переменная с таким именем существует, будет сохранено её прежнее значение.
- EXTR_PREFIX_SAME
- Если переменная с таким именем существует, к её имени будет добавлен префикс, определённый параметром prefix .
- EXTR_PREFIX_ALL
- Добавить префикс prefix ко всем именам переменных. Начиная с PHP 4.0.5, также включает числовые имена.
- EXTR_PREFIX_INVALID
- Добавить префикс prefix только к неприемлемым/числовым именам переменных. Этот флаг был добавлен в PHP 4.0.5.
- EXTR_IF_EXISTS
- Переназначить только переменные, уже имеющиеся в текущей символьной таблице, в противном случае ничего не делать. Данная возможность полезна для определения списка приемлемых переменных и для извлечения только тех переменных, которые вы уже определили из массивов типа $_REQUEST, например. Этот флаг был добавлен в PHP 4.2.0.
- EXTR_PREFIX_IF_EXISTS
- Создать переменные, имена которых начинаются с prefix только если переменная с названием, которому не предшествует prefix , определена в текущей символьной таблице. Этот флаг был добавлен в PHP 4.2.0.
- EXTR_REFS
- Извлечь переменные как ссылки. Это означает, что значения таких переменных будут всё ещё ссылаться на значения массива var_array . Вы можете использовать этот флаг отдельно или комбинировать его с другими, используя OR. Этот флаг был добавлен в PHP 4.3.0.
Если extract_type не определён, он трактуется как EXTR_OVERWRITE.
Обратите внимание, что prefix имеет значение, только если extract_type установлен в EXTR_PREFIX_SAME, EXTR_PREFIX_ALL, EXTR_PREFIX_INVALID или EXTR_PREFIX_IF_EXISTS. Если в результате добавления префикса, не будет получено допустимое имя для переменной, она не будет импортирована в текущую символьную таблицу.
extract() возвращает количество переменных, успешно импортированных в символьную таблицу.
Не используйте функцию extract() для непроверенных данных, таких как пользовательский ввод ($_GET, ...). Если вы сделаете это, например, для того, что бы временно запустить старый код, использующий register_globals, используйте соответствующий флаг extract_type для того, что бы не переназначить уже установленные переменные, такой как EXTR_SKIP и удостоверьтесь, что вы извлекаете содержимое массивов $_SERVER, $_SESSION, $_COOKIE, $_POST и $_GET в этом порядке.
Функцию extract() также можно использовать для импорта в текущую символьную таблицу переменных, содержащихся в ассоциативном массиве, возвращённом функцией wddx_deserialize().
Пример #1 Пример использования extract()
<?php
/* Предположим, что $var_array - это массив, полученный в результате
wddx_deserialize */
$size = "large";
$var_array = array("color" => "blue",
"size" => "medium",
"shape" => "sphere");
extract($var_array, EXTR_PREFIX_SAME, "wddx");
echo "$color, $size, $shape, $wddx_size
";
?>
Результат выполнения данного примера:
blue, large, sphere, medium
Переменная $size не была переназначена, потому что мы определили EXTR_PREFIX_SAME, в результате чего была создана переменная $wddx_size. Если был бы определён флаг EXTR_SKIP, тогда переменная $wddx_size не была бы создана. EXTR_OVERWRITE был бы причиной того, что переменной $size было бы присвоено значение "medium", и EXTR_PREFIX_ALL был бы причиной того, что были бы также созданы новые переменные $wddx_color, $wddx_size и $wddx_shape.
Вы должны использовать ассоциативный массив, использование числовых массивов не приведёт ни к каким результатам, если вы не использууете EXTR_PREFIX_ALL и EXTR_PREFIX_INVALID.
См. также compact().
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Коментарии
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.
If you are working porting an older application, and taking the advice above, extracting only _SERVER, _SESSING, _COOKIE, _POST, _GET, you have forgotten to extract _FILES. Putting _FILES last and using EXTR_SKIP doesn't work because the name of the file upload box is already set as a variable containing only the temporary name of the uploaded file from one of the earlier extracts (I haven't tested to see which one specifically, however). A workaround is to put _FILES last and use EXTR_OVERWRITE. This allows extract to replace that temp-name-only variable with the full array of file upload information.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';
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!)
Here is a little example of how an extraction method should look like when it needs to work recursive (work on nested_arrays too)...
Note that this is only an example, it can be done more easily, and more advanced too.
<?php
/**
* A nested version of the extract () function.
*
* @param array $array The array which to extract the variables from
* @param int $type The type to use to overwrite (follows the same as extract () on PHP 5.0.3
* @param string $prefix The prefix to be used for a variable when necessary
*/
function extract_nested (&$array, $type = EXTR_OVERWRITE, $prefix = '')
{
/**
* Is the array really an array?
*/
if (!is_array ($array))
{
return trigger_error ('extract_nested (): First argument should be an array', E_USER_WARNING);
}
/**
* If the prefix is set, check if the prefix matches an acceptable regex pattern
* (the one used for variables)
*/
if (!empty ($prefix) && !preg_match ('#^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$#', $prefix))
{
return trigger_error ('extract_nested (): Third argument should start with a letter or an underscore', E_USER_WARNING);
}
/**
* Check if a prefix is necessary. If so and it is empty return an error.
*/
if (($type == EXTR_PREFIX_SAME || $type == EXTR_PREFIX_ALL || $type == EXTR_PREFIX_IF_EXISTS) && empty ($prefix))
{
return trigger_error ('extract_nested (): Prefix expected to be specified', E_USER_WARNING);
}
/**
* Make sure the prefix is oke
*/
$prefix = $prefix . '_';
/**
* Loop thru the array
*/
foreach ($array as $key => $val)
{
/**
* If the key isn't an array extract it as we need to do
*/
if (!is_array ($array[$key]))
{
switch ($type)
{
default:
case EXTR_OVERWRITE:
$GLOBALS[$key] = $val;
break;
case EXTR_SKIP:
$GLOBALS[$key] = isset ($GLOBALS[$key]) ? $GLOBALS[$key] : $val;
break;
case EXTR_PREFIX_SAME:
if (isset ($GLOBALS[$key]))
{
$GLOBALS[$prefix . $key] = $val;
}
else
{
$GLOBALS[$key] = $val;
}
break;
case EXTR_PREFIX_ALL:
$GLOBALS[$prefix . $key] = $val;
break;
case EXTR_PREFIX_INVALID:
if (!preg_match ('#^[a-zA-Z_\x7f-\xff]$#', $key{0}))
{
$GLOBALS[$prefix . $key] = $val;
}
else
{
$GLOBALS[$key] = $val;
}
break;
case EXTR_IF_EXISTS:
if (isset ($GLOBALS[$key]))
{
$GLOBALS[$key] = $val;
}
break;
case EXTR_PREFIX_IF_EXISTS:
if (isset ($GLOBALS[$key]))
{
$GLOBALS[$prefix . $key] = $val;
}
break;
case EXTR_REFS:
$GLOBALS[$key] =& $array[$key];
break;
}
}
/**
* The key is an array... use the function on that index
*/
else
{
extract_nested ($array[$key], $type, $prefix);
}
}
}
?>
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!
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.
Experimentally I found that calling extract() also shows the number of keys if the key is set and is not numeric ! Maybe there was a better definition than mine . Please have a look to this scripts :
<?PHP
$var["i"] = "a";
$var["j"] = "b";
$var["k"] = 1;
echo extract($var); // returns 3
?>
<?PHP
$var2["i"] = "a";
$var2[2] = "b";
$var2[] = 1;
echo extract($var2); // returns 1
?>
(Arash Moslehi)
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.
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 );
?>
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 $is_admin = true attack)
I would draw your attention to the user note at the very end of this page regarding PREFIXES. The user points out that php adds a '_' to your prefixes.Following up on ktwombley at gmail dot com's post:
Presumably one easy way of dealing with this security issue is to use the EXTR_IF_EXISTS flag and make sure
a) your define acceptable input variables beforehand (i.e. as empty variables)
b) Sanitise any user input to avoid unacceptable variable content.
If you do these two things, then I'm not sure I see the difference between extract($_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.
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.
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.
When using EXTR_PREFIX_ALL - and probably all the other EXTR_PREFIX_* constants - and a numerically-indexed array, extract() will add an underscore ("_") between the prefix and the index.
<?php
extract(array('foo', 'bar'), EXTR_PREFIX_ALL, 'var');
print_r(get_defined_vars()); // Reveals $var_0 = 'foo' and $var_1 = 'bar'
?>
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.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.
You can't extract a numeric indexed array(e.g. non-assoc array).
<?php
$a = array(
1,
2
);
extract($a);
var_dump(${1});
?>
result:
PHP Notice: Undefined variable: 1 in /Users/Lutashi/t.php on line 7
Notice: Undefined variable: 1 in /Users/Lutashi/t.php on line 7
NULL
It is possible to use this as a way to create public attributes for a class.
<?php
class Foo {
public function __construct ($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
?>
[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;
}
?>
[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) ""
}
}
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.
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.
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
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.
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
In response to Dan O'Donnell's note:
"Presumably one easy way of dealing with this security issue is to use the EXTR_IF_EXISTS flag and make sure"
Not necessarily - even using the EXTR_IF_EXISTS flag could be extremely dangerous - imagine this code running...
<?php
global $sql ;
function runSql ()
{
$result = $conn->query($sql);
$conn-> close();
return $result;
}
function extractGet ()
{
$name = '' ;
$address = '' ;
foreach ( $_GET as $key => $value )
$_GET[$key] = urldecode ( $value ) ;
extract($_GET,EXTR_IF_EXISTS);
$sql = str_replace ( '{NAME}', $name, $sql ) ;
$sql = str_replace ( '{ADDRESS}', $address, $sql ) ;
}
function outputResult ( $res )
{
echo '<pre>'.print_r ( $res->fetch_array(MYSQLI_NUM) ).'</pre>' ;
}
$sql = 'SELECT postcode FROM Customers WHERE name={NAME} AND address={ADDRESS}';
extractGet () ;
$res = runSql () ;
outputResult ( $res ) ;
?>
Now can you see a massive security issue here...
seems all well and good if we had a url like
mycode.php?name=joe%20bloggs&address=20%20Any%20Street
as that would specifically find joe bloggs of 20 any street.
however what if someone typed in
mycode.php?sql=SELECT%20password%20FROM%20Customers
or even worse
mycode.php?sql=DELETE%20from%20Customers
The problem here is that even though as far as you're aware you defined both name and address as the only two empty variables within that function - you may have forgotten about global variables, and these global variables could cause major security issues
In the example above $sql is defined as "SELECT postcode FROM Customers WHERE name={NAME} AND address={ADDRESS}" which seems all well and good, and safe, and then later on str_replace in the extractGet function replaces {NAME} and {ADDRESS} with the name and address variables from $_GET - but if GET contains an SQL variable then that would overwrite the global $sql variable before the str_replace function - and if the str_replace function finds no matches it just returns the original string - in the above two examples the SQL string would be "SELECT password FROM Customers" which in the example outputResult just prints the data retrieved from the database and so in this stage it could print all the customers passwords (hopefully encrypted!) to the screen (oops!) or in the second example the SQL string would be "DELETE from Customers" - with no WHERE clause that would delete all the data from the Customers table and of course a combination of
SELECT table_name FROM information_schema.tables
and
DROP TABLE <table_name>
could be a real disaster!
Of course, this is only a basic example, but it could be quite easy to forget about global variables and these global variables could quite easily be used with extract to cause serious security risks if GET, REQUEST or POST is sent to extract!