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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>
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。

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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