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<refentry id="function.extract">
 <refnamediv>
  <refname>extract</refname>
  <refpurpose>Import variables into the current symbol table from an array</refpurpose>
 </refnamediv>
 <refsect1>
  <title>Description</title>
  <methodsynopsis>
   <type>int</type><methodname>extract</methodname>
   <methodparam><type>array</type><parameter>var_array</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>extract_type</parameter></methodparam>
   <methodparam choice="opt"><type>string</type><parameter>prefix</parameter></methodparam>
  </methodsynopsis>
  <para>
   This function is used to import variables from an array into the
   current symbol table.  It takes an associative array
   <parameter>var_array</parameter> and treats keys as variable
   names and values as variable values.  For each key/value pair it
   will create a variable in the current symbol table, subject to
   <parameter>extract_type</parameter> and
   <parameter>prefix</parameter> parameters.
  </para>
  <note>
   <para>
    Beginning with version 4.0.5, this function returns the number of
    variables extracted.
   </para>
  </note>
  <note>
   <para>
    <constant>EXTR_IF_EXISTS</constant> and <constant>EXTR_PREFIX_IF_EXISTS</constant> were introduced in version 4.2.0.
   </para>
  </note>
  <note>
   <para>
    <constant>EXTR_REFS</constant> was introduced in version 4.3.0.
   </para>
  </note>
  <para>
   <function>extract</function> checks each key to see whether it
   has a valid variable name. It also checks for collisions with
   existing variables in the symbol table. The way invalid/numeric
   keys and collisions are treated is determined by the
   <parameter>extract_type</parameter>. It can be one of the
   following values:
   <variablelist>
    <varlistentry>
     <term><constant>EXTR_OVERWRITE</constant></term>
     <listitem>
      <simpara>
       If there is a collision, overwrite the existing variable.
      </simpara>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><constant>EXTR_SKIP</constant></term>
     <listitem>
      <simpara>
       If there is a collision, don't overwrite the existing
       variable.
      </simpara>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><constant>EXTR_PREFIX_SAME</constant></term>
     <listitem>
      <simpara>If there is a collision, prefix the variable name with
      <parameter>prefix</parameter>.
      </simpara>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><constant>EXTR_PREFIX_ALL</constant></term>
     <listitem>
      <simpara>
       Prefix all variable names with
       <parameter>prefix</parameter>. Beginning with PHP 4.0.5, this includes
       numeric variables as well.
      </simpara>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><constant>EXTR_PREFIX_INVALID</constant></term>
     <listitem>
      <simpara>
       Only prefix invalid/numeric variable names with
       <parameter>prefix</parameter>. This flag was added in
       PHP 4.0.5.
      </simpara>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><constant>EXTR_IF_EXISTS</constant></term>
     <listitem>
      <simpara>
       Only overwrite the variable if it already exists in the
       current symbol table, otherwise do nothing.  This is useful
       for defining a list of valid variables and then extracting
       only those variables you have defined out of $_REQUEST, for
       example.  This flag was added in PHP 4.2.0.
      </simpara>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><constant>EXTR_PREFIX_IF_EXISTS</constant></term>
     <listitem>
      <simpara>
       Only create prefixed variable names if the non-prefixed version
       of the same variable exists in the current symbol table.  This
       flag was added in PHP 4.2.0.
      </simpara>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><constant>EXTR_REFS</constant></term>
     <listitem>
      <simpara>
       Extracts variables as references. This effectively means that the
       values of the imported variables are still referencing the values of
       the <parameter>var_array</parameter> parameter. You can use this flag
       on its own or combine it with any other flag by OR'ing the
       <parameter>extract_type</parameter>. This flag was added in PHP
       4.3.0.
      </simpara>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
  <para>
   If <parameter>extract_type</parameter> is not specified, it is
   assumed to be <constant>EXTR_OVERWRITE</constant>.
  </para>
  <para>
   Note that <parameter>prefix</parameter> is only required if
   <parameter>extract_type</parameter> is <constant>EXTR_PREFIX_SAME</constant>,
   <constant>EXTR_PREFIX_ALL</constant>, <constant>EXTR_PREFIX_INVALID</constant>
   or <constant>EXTR_PREFIX_IF_EXISTS</constant>. If
   the prefixed result is not a valid variable name, it is not
   imported into the symbol table. Prefixes are automatically separated from
   the array key by an underscore character.
  </para>
  <para>
   <function>extract</function> returns the number of variables
   successfully imported into the symbol table.
  </para>
  <warning>
   <para>
    Do not use <function>extract</function> on untrusted data, like
    user-input ($_GET, ...). If you do, for example, if you want to run old
    code that relies on
    <link linkend="security.globals">register_globals</link>
    temporarily, make sure you use one of the non-overwriting
    <parameter>extract_type</parameter> values such as
    <constant>EXTR_SKIP</constant> and be aware that you should extract
    in the same order that's defined in
    <link linkend="ini.variables-order">variables_order</link> within the
    <link linkend="ini">&php.ini;</link>.
   </para>
  </warning>
  <para>
   A possible use for <function>extract</function> is to import into the
   symbol table variables contained in an associative array returned by
   <function>wddx_deserialize</function>.
  </para>
  <para>
   <example>
    <title><function>extract</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php

/* Suppose that $var_array is an array returned from
   wddx_deserialize */

$size = "large";
$var_array = array("color" => "blue",
                   "size"  => "medium",
                   "shape" => "sphere");
extract($var_array, EXTR_PREFIX_SAME, "wddx");

echo "$color, $size, $shape, $wddx_size\n";

?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
blue, large, sphere, medium
]]>
    </screen>
   </example>
  </para>
  <para>
   The <varname>$size</varname> wasn't overwritten, because we
   specified <constant>EXTR_PREFIX_SAME</constant>, which resulted in
   <varname>$wddx_size</varname> being created.  If <constant>EXTR_SKIP</constant> was
   specified, then $wddx_size wouldn't even have been created.
   <constant>EXTR_OVERWRITE</constant> would have caused <varname>$size</varname> to have
   value "medium", and <constant>EXTR_PREFIX_ALL</constant> would result in new variables
   being named <varname>$wddx_color</varname>,
   <varname>$wddx_size</varname>, and
   <varname>$wddx_shape</varname>.
  </para>
  <para>
   You must use an associative array, a numerically indexed array
   will not produce results unless you use <constant>EXTR_PREFIX_ALL</constant> or
   <constant>EXTR_PREFIX_INVALID</constant>.
  </para>
  <para>
   See also <function>compact</function>.
  </para>
 </refsect1>
</refentry>

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