PHP extract() function (array split) definition and usage

$a = 'Original';
$my_array = array("a" => "Cat","b" => "Dog", "c" => " Horse");
extract($my_array);
echo "$a = $a; $b = $b; $c = $c";
?>

Output:

$a = Cat; $b = Dog; $c = Horse

Example 2 Use all parameters:

$a = 'Original';
$my_array = array("a" => "Cat","b" => "Dog", " c" => "Horse");
extract($my_array, EXTR_PREFIX_SAME, 'dup');
echo "$a = $a; $b = $b; $c = $c; $dup_a = $dup_a;";
?>

output: $a = Original; $b = Dog; $c = Horse; $dup_a = Cat;

PHP extract() function

Recently, when I was looking at the code of an awesome person, I saw a very useful function: extract(). Its main function is to expand the array. The key name is used as the variable name, and the element value is the variable value. It can be said to be an array operation. Provides another convenient tool than Fang said that it is easy to extract the elements of $_POST or $_GET. You cannot assign values ​​to the content submitted in the form one by one. You can directly use the following code:

form.html

In action.php, just use the extract() function to extract the $_POST global data: action.php

extract($_POST);
//Equivalent to $username = $_POST['username'];
//$password = $_POST['password'];
?> ;

The following is a detailed explanation in the php manual:

extract (PHP 4, PHP 5)

extract — Import variables from an array into the current symbol table

Instructions int extract (array $var_array [, int $extract_type [, string $prefix ]] )

This function is used to import variables from the array into the current symbol table. Accepts the associative array var_array as argument and uses the key name as the variable name and the value as the variable value. For each key/value pair a variable is created in the current symbol table and subject to Effect of extract_type and prefix parameters.

Note: Since version 4.0.5 this function returns the number of variables extracted. Note: EXTR_IF_EXISTS and EXTR_PREFIX_IF_EXISTS were introduced in version 4.2.0. Note: EXTR_REFS was introduced in version 4.3.0.

extract() checks each key name to see if it can be used as a legal variable name, and also checks for conflicts with existing variable names in the symbol table. The treatment of illegal/numeric and conflicting key names will be determined by the extract_type parameter. Can be One of the following values:

EXTR_OVERWRITE If there is a conflict, existing variables are overwritten. EXTR_SKIP If there is a conflict, existing variables are not overwritten. EXTR_PREFIX_SAME If there is a conflict, prefix the variable name with prefix . EXTR_PREFIX_ALL Prefix all variable names with prefix . Since PHP 4.0.5 this also includes handling of numeric indexes. EXTR_PREFIX_INVALID Prefix only illegal/numeric variable names with prefix . This tag is newly added in PHP 4.0.5. EXTR_IF_EXISTS Overwrite the values ​​of variables with the same name only if they already exist in the current symbol table. Others are not processed. It can be used when a set of legal variables has been defined, and then you want to overwrite these variables by extracting values ​​from an array such as $_REQUEST. This mark is New in PHP 4.2.0. EXTR_PREFIX_IF_EXISTS Only when a variable with the same name already exists in the current symbol table, a variable name with a prefix is ​​created, and nothing else is processed. This tag is newly added in PHP 4.2.0. EXTR_REFS Extract the variable as a reference. This is a strong indication that the imported variable still references the value of the var_array parameter. This flag can be used alone or in combination with any other flag using OR in extract_type. This tag is PHP 4.3.0 Newly added. If extract_type is not specified, EXTR_OVERWRITE is assumed.

Note that prefix is ​​only required if the value of extract_type is EXTR_PREFIX_SAME, EXTR_PREFIX_ALL, EXTR_PREFIX_INVALID or EXTR_PREFIX_IF_EXISTS. If the result after appending the prefix is ​​not a legal variable name, Will not be imported into the symbol table. An underscore is automatically added between the prefix and the array key name.

extract() returns the number of variables successfully imported into the symbol table.

Warning

Don’t use extract() on data that cannot be trusted, such as user input ($_GET,…). If you do this, for example, to temporarily run old code that depends on register_globals, make sure to use an extract_type value that will not overwrite , such as EXTR_SKIP, and note that they should be extracted in the order defined by variables_order in php.ini.

One possible use of

extract() is to import the contents of the combined array returned by wddx_deserialize() into a symbol table variable.

Example:

/* Assume $var_array is the array returned by 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_sizen";
 ?>

output: blue, large, sphere, medium

$size is not overridden because EXTR_PREFIX_SAME is specified, which causes $wddx_size to be built. If EXTR_SKIP is specified, $wddx_size will not be created either. EXTR_OVERWRITE will make the value of $size For "medium", EXTR_PREFIX_ALL will create new variables $wddx_color, $wddx_size and $wddx_shape.

Associative arrays must be used, numerically indexed arrays will not produce results unless EXTR_PREFIX_ALL or EXTR_PREFIX_INVALID is used.