PHP, Structures and Functions of ARRAY

This function, This function treats keys as variable names and values as variable values.

For each key/value pair it will create a variable in the current symbol table, subject to $flags and $prefix parameters.

We must use an associative ARRAY; a numerically indexed ARRAY will not produce results unless you use EXTR_PREFIX_ALL or EXTR_PREFIX_INVALID.

Worth noting that $prefix is only required if $flags is EXTR_PREFIX_SAME, EXTR_PREFIX_ALL, EXTR_PREFIX_INVALID or EXTR_PREFIX_IF_EXISTS.

If the prefixed result is not a valid variable name, it is not imported into the symbol table.

Prefixes are automatically separated from the array key by an underscore character.


<?php

int extract ( arr &$array [, int $flags = EXTR_OVERWRITE [, 
                                          str $prefix = NULL ]] )


where,

&$array = An associative ARRAY
                ( PASSED by reference )

$flags = To control the way  invalid/numeric keys and
                     collisions are treated is determined by the extraction
             ( SEE the below TABLE )
                
$prefix = The prefix to consider or not

?>

&$array

An associative ARRAY where the variables will be imported

$flags

The way invalid/numeric keys and collisions are treated is determined by the extraction flags.

It can be one of the following values:

CONSTANT	VALUE	OBSERVATIONS
EXTR_OVERWRITE DEFAULT	0	If there is a collision, overwrite the existing variable.
EXTR_SKIP	1	If there is a collision, don't overwrite the existing variable
EXTR_PREFIX_SAME	2	If there is a collision, prefix the variable name with $prefix.
EXTR_PREFIX_ALL	3	Prefix variable names with $prefix.
EXTR_PREFIX_INVALID	4	Only prefix invalid/numeric variable names with $prefix.
EXTR_PREFIX_IF_EXISTS	5	Only create prefixed variable names if the non-prefixed version of the same variable exists in the current symbol table.
EXTR_IF_EXISTS	6	Only overwrite the variable if it already exists in the current symbol table, otherwise do nothing. This is useful for defining a list of valid variables and then extracting only those variables you have defined out of $_REQUEST, for example.
EXTR_REFS	256	Extracts variables as references. This effectively means that the values of the imported variables are still referencing the values of the $array parameter. You can use this flag alone or combine it with any other flag using the $flags signaling.
ed48

$prefix

The prefix of the variable to be considered or not.

WARNING

Do not use this function on untrusted data, like user input, (i.e. $_GET, $_FILES, etc.).

If you do, for example if you want to temporarily run old code that relied on register_globals, make sure you use one of the non-overwriting $flags values such as EXTR_SKIP and be aware that you should extract in the same order that's defined in variables_order within the php.ini.

If you still have register_globals and it is turned on, if you use this function on $_FILES and specify EXTR_SKIP, you may be surprised at the results.

This is not recommended practice and is only documented here for for didactic reasons.

The use of register_globals is deprecated.

A possible use for this function is to import into the symbol table variables contained in an associative array returned by the function wddx_deserialize, however, this will be removed in PHP 7.4.0.

EXERCISE


<?php

$colorblue = "AERO BLUE";
$colorgreen = "AVOCADO";
$colorred= "AMERICAN ROSE";

$arr01 = [ "red" => "#FF033E", 
            "green" => "#568203", 
              "blue" => "#C9FFE5" ];

extract($arr01, EXTR_OVERWRITE);

echo '<pre>';
print_r($arr01);

echo '</pre><br><br>' . $colorred . 
                        '&nbsp;= &nbsp;' . 
                                    $red . '<br><br>';

echo $colorgreen . 
                        '&nbsp;=&nbsp;' . 
                                    $green . '<br><br>';

echo $colorblue . 
                        '&nbsp;=&nbsp;' . 
                                    $blue . '<br>';

?>

EXERCISE


<?php

$arr0102 = [ 'f1' => "Apple", 
                    'f2' => "Strawberry", 
                    'f3' => "Pineapple", 
                    'f4' => "Banana", 
                    'f5' => "Orange" ];
                
extract($arr0102, EXTR_PREFIX_SAME, NULL);
                
echo $f1, ' is red, ', $f5, ' is orange.' . '<br>';
                          
?>

EXERCISE


<?php

$data03 = 'AEAD.txt';
// See the below file

$rdata03 = file_get_contents($data03);

echo $rdata03 . '<br>';

$xdata03 = explode('<br>', $rdata03);

extract($_FILES, 256);
// 256 = EXTR_REFS

echo $xdata03[2] . '<br>';
                         
?>


AEAD, Autenticated Encryption with 
Associated Data, is a form of encryption which 
simultaneously provides confidentiality, integrity, 
and authenticity assurances on the data.<br><br>GCM, Galois/Counter Mode
 is a mode of operation for symmetric key cryptographic
 block ciphers that has been widely adopted because of 
 its efficiency and performance.<br><br>
GCM throughput rates for state-of-the-art, 
high-speed communication channels can be achieved 
with reasonable hardware resources.<br><br>
CCM, (Counter with CBC-MAC) is a mode of operation 
for cryptographic block ciphers.
It is an authenticated encryption algorithm designed 
to provide both authentication and confidentiality.<br><br>
CCM mode is only defined for block ciphers with a 
block length of 128 bits.<br><br>

EXERCISE


<?php

$val = 4;
$str = "John";

debug_zval_dump($val);
echo '<br>'; 
debug_zval_dump($str);
echo '<br><br>'; 

/* Extracting Global Variables */
var_dump(extract($GLOBALS, EXTR_REFS));
echo '<br>'; 
debug_zval_dump($val);
echo '<br>'; 
debug_zval_dump($str);

?>

EXERCISE


<?php

/* various combinations of arrays
                     to be used for the test */
$mixed_array = array(
array(),
array( 1,2,3,4,5,6,7,8,9 ),
array( "One", "Two", "Three", "Four", "Five" ),
);

$counter = 0;

foreach ( $mixed_array as $sub_array ) {
echo "<br><br>Iteration: $counter<br><br>";
$counter++;

var_dump ( extract($sub_array));
/* Single Argument */
echo '<br><br>';
/* variations of two arguments */
var_dump ( extract($sub_array, EXTR_OVERWRITE));
echo '<br>';
var_dump ( extract($sub_array, EXTR_SKIP));
echo '<br>';
var_dump ( extract($sub_array, EXTR_IF_EXISTS));
echo '<br><br>';
/* variations of three arguments 
          with use of various extract types */
var_dump ( extract($sub_array, EXTR_PREFIX_INVALID, "ssd"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_SAME, "sss"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_ALL, "bb"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_ALL, ""));
// "_" taken as default prefix
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_IF_EXISTS, "bb"));
}

?>

EXERCISE


<?php

/* various combinations of arrays 
               to be used for the test */
$mixed_array = array(
array( 6, "six", 7, "seven", 8, "eight", 9, "nine" ),
array( "a" => "aaa", "A" => "AAA", 
                      "c" => "ccc", "d" => "ddd", "e" => "eee" ),
array( "1" => "one", "2" => "two", 
            "3" => "three", "4" => "four", "5" => "five" ),
);

$counter = 0;

foreach ( $mixed_array as $sub_array ) {
echo "<br><br>Iteration: $counter<br><br>";
$counter++;

var_dump ( extract($sub_array));
/* Single Argument */
echo '<br>';
/* variations of two arguments */
var_dump ( extract($sub_array, EXTR_OVERWRITE));
echo '<br>';
var_dump ( extract($sub_array, EXTR_SKIP));
echo '<br>';
var_dump ( extract($sub_array, EXTR_IF_EXISTS));
echo '<br><br>';

/* variations of three arguments 
           with use of various extract types*/
var_dump ( extract($sub_array, EXTR_PREFIX_INVALID, "ssd"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_SAME, "sss"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_ALL, "bb"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_ALL, ""));
// "_" taken as default prefix
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_IF_EXISTS, "bb"));
}

?>

EXERCISE


<?php

$mixed_array = array(
array( 1 => "one", 2 => "two", 3 => 7, 
                     4 => "four", 5 => "five" ),
array( "f" => "fff", "1" => "one", 4 => 6, 
               "" => "blank", 2.4 => "float", "F" => "FFF",
               "blank" => "", 3.7 => 3.7,
               5.4 => 7, 6 => 8.6, '5' => "Five", 
               "4name" => "jonny", "a" => NULL, 
               NULL => 3 ),
array( 12, "name", 'age', '45' ),
);

$counter = 0;

foreach ( $mixed_array as $sub_array ) {
echo "<br><br>Iteration: $counter<br><br>";
$counter++;

var_dump ( extract($sub_array)); 
/* Single Argument */
 echo '<br>';
/* variations of two arguments */
var_dump ( extract($sub_array, EXTR_OVERWRITE));
 echo '<br>';
var_dump ( extract($sub_array, EXTR_SKIP));
 echo '<br>';
var_dump ( extract($sub_array, EXTR_IF_EXISTS));
 echo '<br><br><br>';

/* variations of three arguments 
             with use of various extract types*/
var_dump ( extract($sub_array, EXTR_PREFIX_INVALID, "ssd"));
 echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_SAME, "sss"));
 echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_ALL, "bb"));
 echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_ALL, ""));
// "_" taken as default prefix
 echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_IF_EXISTS, "bb"));
}

?>

EXERCISE


<?php

$mixed_array = array(
  array( array("oNe", "tWo", 4), 
  array(10, 20, 30, 40, 50), array() ),
  array( "one" => 1, "one" => 2, "three" => 3, 
                3, 4, 3 => 33, 4 => 44, 5, 6,
               5.4 => 54, 5.7 => 57, 
               "5.4" => 554, "5.7" => 557 )
);

$counter = 0;

foreach ( $mixed_array as $sub_array ) {
  echo "<br><br>Iteration: $counter<br><br>";
  $counter++;

  var_dump ( extract($sub_array));
  /* Single Argument */
  echo '<br>';
  /* variations of two arguments */
  var_dump ( extract($sub_array, EXTR_OVERWRITE));
  echo '<br>';
  var_dump ( extract($sub_array, EXTR_SKIP));
  echo '<br>';
  var_dump ( extract($sub_array, EXTR_IF_EXISTS));
  echo '<br><br><br>';

/* variations of three arguments 
              with use of various extract types*/
var_dump ( extract($sub_array, EXTR_PREFIX_INVALID, "ssd"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_SAME, "sss"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_ALL, "bb"));
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_ALL, ""));
// "_" taken as default prefix
echo '<br>';
var_dump ( extract($sub_array, EXTR_PREFIX_IF_EXISTS, "bb"));
}

?>

EXERCISE


<?php

/* EXTR_REFS as second Argument */
$a = array ('foo' => 'aaa');

echo 'The given $a:<br>';
var_dump($a);

echo '<br><br>After extract($a, EXTR_REFS):<br>';          
var_dump ( extract($a, EXTR_REFS));
echo '<br><br>$foo:<br>';
var_dump($foo);

$b = $a;
$b['foo'] = 'bbb';
echo '<br><br>$b:<br>';
var_dump($b);

echo '<br><br>After extract($a, EXTR_REFS):<br>';
var_dump ( extract($a, EXTR_REFS));
echo '<br><br>$foo:<br>';
var_dump($foo);
echo '<br><br>$a:<br>';
var_dump($a);

?>

EXERCISE


<?php

/* EXTR_PREFIX_ALL called twice with same prefix string */
echo "Testing for 
               EXTR_PREFIX_ALL 
                   called twice with same prefix string.<br><br>";
                   
$a = array( "1" => "one", 
                  "2" => "two", 
                  "3" => "three", 
                  "4" => "four", 
                  "5" => "five" );
                  
echo 'The given $a:<br>';
var_dump($a);

echo '<br><br>After extract($a, EXTR_PREFIX_ALL, "same"):<br>';  
var_dump ( extract($a, EXTR_PREFIX_ALL, "same"));

$b = array( "f" => "fff", 
                   "1" => "one", 
                    4 => 6, 
                   "" => "blank", 
                  2.4 => "float", 
                   "F" => "FFF", 
            "blank" => "", 
                   3.7 => 3.7, 
                   5.4 => 7, 
                   6 => 8.6, 
                  '5' => "Five", 
        "4name" => "jonny", 
                "a" => NULL, 
            NULL => 3 );
            
echo '<br><br>The given $b:<br>';
var_dump($b);

echo '<br><br>After extract($b, EXTR_PREFIX_ALL, "same"):<br>';                 
var_dump ( extract($b, EXTR_PREFIX_ALL, "same"));
echo '<br><br>After extract($b, EXTR_PREFIX_ALL, "diff"):<br>';  
var_dump ( extract($b, EXTR_PREFIX_ALL, "diff"));

?>

EXERCISE


<?php

/* To show variables with numerical 
            prefixes cannot be extracted */
$var["i"] = 1;
$var["j"] = 2;
$var["k"] = 3;
echo "Testing for Numerical prefixes.<br><br>";
var_dump(extract($var));

$var1["m"] = 1;
$var1[2] = 2;
$var1[] = 3;
var_dump ( extract($var1));

?>

EXERCISE


<?php

$a = array('foo' => 'original.foo');
$nonref = $a['foo'];
$ref = &$a;
extract($a, EXTR_REFS);
$a['foo'] = 'changed.foo';
var_dump($nonref);

?>

EXERCISE


<?php

$a = array('foo' => 'original.foo');
$ref = &$a;
$foo = 'test';
extract($a, EXTR_OVERWRITE|EXTR_REFS);
$foo = 'changed.foo';
var_dump($a['foo']);

?>