Definition and usage of extract() function in PHP_PHP Tutorial

定义和用法

PHP extract() 函数从数组中把变量导入到当前的符号表中。

对于数组中的每个元素，键名用于变量名，键值用于变量值。

第二个参数 type 用于指定当某个变量已经存在，而数组中又有同名元素时，extract() 函数如何对待这样的冲突。

本函数返回成功设置的变量数目。

语法
extract(array,extract_rules,prefix)

参数	描述
array	必需。规定要使用的输入。
extract_rules	可选。extract() 函数将检查每个键名是否为合法的变量名，同时也检查和符号表中的变量名是否冲突。 对非法、数字和冲突的键名的处理将根据此参数决定。可以是以下值之一： 可能的值： EXTR_OVERWRITE - 默认。如果有冲突，则覆盖已有的变量。 EXTR_SKIP - 如果有冲突，不覆盖已有的变量。（忽略数组中同名的元素） EXTR_PREFIX_SAME - 如果有冲突，在变量名前加上前缀 prefix。自 PHP 4.0.5 起，这也包括了对数字索引的处理。 EXTR_PREFIX_ALL - 给所有变量名加上前缀 prefix（第三个参数）。 EXTR_PREFIX_INVALID - 仅在非法或数字变量名前加上前缀 prefix。本标记是 PHP 4.0.5 新加的。 EXTR_IF_EXISTS - 仅在当前符号表中已有同名变量时，覆盖它们的值。其它的都不处理。可以用在已经定义了一组合法的变量，然后要从一个数组例如 $_REQUEST 中提取值覆盖这些变量的场合。本标记是 PHP 4.2.0 新加的。 EXTR_PREFIX_IF_EXISTS - 仅在当前符号表中已有同名变量时，建立附加了前缀的变量名，其它的都不处理。本标记是 PHP 4.2.0 新加的。 EXTR_REFS - 将变量作为引用提取。这有力地表明了导入的变量仍然引用了 var_array 参数的值。可以单独使用这个标志或者在 extract_type 中用 OR 与其它任何标志结合使用。本标记是 PHP 4.3.0 新加的。
prefix	可选。请注意 prefix 仅在 extract_type 的值是 EXTR_PREFIX_SAME，EXTR_PREFIX_ALL，EXTR_PREFIX_INVALID 或 EXTR_PREFIX_IF_EXISTS 时需要。如果附加了前缀后的结果不是合法的变量名，将不会导入到符号表中。 前缀和数组键名之间会自动加上一个下划线。

Example 1


Output:

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

Example 2

Use all parameters:



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 that it is an array. Operation provides another convenient tool. For example, you can easily extract the elements of $_POST or $_GET. You cannot assign values ​​to the contents 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



Isn’t it very convenient? Haha, here is the detailed explanation in the PHP manual:

extract
(PHP 4, PHP 5)

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

Description
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, affected by the 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
Overwrite existing variables if there is a conflict.
EXTR_SKIP
If there is a conflict, existing variables will not be 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
Only prefix illegal/numeric variable names with prefix . This tag is newly added in PHP 4.0.5.
EXTR_IF_EXISTS
Only overwrite the values ​​of variables with the same name 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 tag is newly added 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 will be created, and nothing else will be processed. This tag is newly added in PHP 4.2.0.
EXTR_REFS
Extract variables as references. 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 newly added in PHP 4.3.0.
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, it 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

Do not 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 relies on register_globals, be sure to use an extract_type value that will not overwrite, such as EXTR_SKIP, and note that extraction should be 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#1 extract() Example

The above example will output:

blue, large, sphere, medium

$size is not overridden because it is specified EXTR_PREFIX_SAME, which causes $wddx_size to be created. If EXTR_SKIP is specified, $wddx_size will not be created either. EXTR_OVERWRITE will make $size have the value "medium" and 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.