Analysis of the magical uses of extract() function in PHP_PHP Tutorial

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 provides functions for the operation of the array. Another convenient tool is provided. For example, you can easily extract the elements of $_POST or $_GET. You have to 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

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 middle. 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 EXTR_PREFIX_SAME is specified, which causes $wddx_size to be established. 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.