A brief analysis of PHP function extract() application skills

A brief analysis of PHP function extract() application skills_PHP tutorial

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Release： 2016-07-15 13:35:00

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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. Use the following code directly. ：

form.html

< form action=" action.php" method="post">
< input type ="text" name="username">
< input type="password" name ="password">
< input type="submit"> ;

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

< form action="action.php" method="post">
< input type="text" name="username">
< input type="password" name="password">
< input type="submit">

是不是很方便呢？呵呵，下面是PHP手册里对于PHP函数extract()的详细解释：

extract
(PHP 4, PHP 5)

extract — 从数组中将变量导入到当前的符号表

说明

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

PHP函数extract()用来将变量从数组中导入到当前的符号表中。接受结合数组 var_array 作为参数并将键名当作变量名，值作为变量的值。对每个键／值对都会在当前的符号表中建立变量，并受到 extract_type 和 prefix 参数的影响。

Note: 自版本 4.0.5 起本函数返回被提取的变量数目。

Note: EXTR_IF_EXISTS 和 EXTR_PREFIX_IF_EXISTS 是版本 4.2.0 中引进的。

Note: EXTR_REFS 是版本 4.3.0 中引进的。

PHP函数extract()检查每个键名看是否可以作为一个合法的变量名，同时也检查和符号表中已有的变量名的冲突。对待非法／数字和冲突的键名的方法将根据 extract_type 参数决定。可以是以下值之一：

EXTR_OVERWRITE
如果有冲突，覆盖已有的变量。

EXTR_SKIP
如果有冲突，不覆盖已有的变量。

EXTR_PREFIX_SAME
如果有冲突，在变量名前加上前缀 prefix 。

EXTR_PREFIX_ALL
给所有变量名加上前缀 prefix 。自 PHP 4.0.5 起这也包括了对数字索引的处理。

EXTR_PREFIX_INVALID
仅在非法／数字的变量名前加上前缀 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。
如果没有指定 extract_type ，则被假定为 EXTR_OVERWRITE。

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

Example#1 extract() Example

<ol class="dp-xml">
<li class="alt"><span><span class="tag"><</span><span> ?php  </span></span></li><li><span>/* 假定 $var_array 是 wddx_<br />deserialize 返回的数组*/  </span></li><li class="alt"><span>$</span><span class="attribute">size</span><span> = &ldquo;large&rdquo;;  </span></li><li><span>$</span><span class="attribute">var_array</span><span> = array(&rdquo;color&rdquo; =</span><span class="tag">></span><span> “blue”,  </span></span></li>
<li class="alt">
<span>“size” =</span><span class="tag">></span><span> “medium”,  </span>
</li>
<li>
<span>“shape” =</span><span class="tag">></span><span> “sphere”);  </span>
</li>
<li class="alt"><span>extract($var_array, EXTR_<br>PREFIX_SAME, “wddx”);  </span></li>
<li><span>echo “$color, $size, $shape, $wddx_sizen”;  </span></li>
<li class="alt">
<span class="tag">?></span><span> </span>
</li>
</ol>

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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 built. 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.

The PHP function extract() must use an associative array. Numerically indexed arrays will not produce results unless EXTR_PREFIX_ALL or EXTR_PREFIX_INVALID is used.