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<p class="sycode"> <p class="sycode"> extract ( array , extract_rules , prefix) </p> </p><p> </p>
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。 |
例子 1
<p class="sycode"> <p class="sycode"> <? php $a = ' Original ' ; $my_array = array ( " a " => " Cat " , " b " => " Dog " , " c " => " Horse " ); extract ( $my_array ); echo " \ $a = $a ; \ $b = $b ; \ $c = $c " ; ?> </p> </p><p> </p>
输出:
<p class="sycode"> <p class="sycode"> $a = Cat; $b = Dog; $c = Horse </p> </p><p> </p>
例子 2
使用全部参数:
<p class="sycode"> <p class="sycode"> <? php $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 ; " ; ?> </p> </p><p> </p>
输出:
<p class="sycode"> <p class="sycode"> $a = Original; $b = Dog; $c = Horse; $dup_a = Cat; </p> </p><p> </p>

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PHP has shaped the network over the past few decades and will continue to play an important role in web development. 1) PHP originated in 1994 and has become the first choice for developers due to its ease of use and seamless integration with MySQL. 2) Its core functions include generating dynamic content and integrating with the database, allowing the website to be updated in real time and displayed in personalized manner. 3) The wide application and ecosystem of PHP have driven its long-term impact, but it also faces version updates and security challenges. 4) Performance improvements in recent years, such as the release of PHP7, enable it to compete with modern languages. 5) In the future, PHP needs to deal with new challenges such as containerization and microservices, but its flexibility and active community make it adaptable.

The core benefits of PHP include ease of learning, strong web development support, rich libraries and frameworks, high performance and scalability, cross-platform compatibility, and cost-effectiveness. 1) Easy to learn and use, suitable for beginners; 2) Good integration with web servers and supports multiple databases; 3) Have powerful frameworks such as Laravel; 4) High performance can be achieved through optimization; 5) Support multiple operating systems; 6) Open source to reduce development costs.


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