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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>
      EXTR_IF_EXISTS and EXTR_PREFIX_IF_EXISTS was introduced in version 4.2.0.
     </para>
    </note>
    <note>
     <para>
      EXTR_REFS 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>EXTR_OVERWRITE</term>
       <listitem>
        <simpara>
         If there is a collision, overwrite the existing variable.
        </simpara>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>EXTR_SKIP</term>
       <listitem>
        <simpara>
         If there is a collision, don't overwrite the existing
         variable.
        </simpara>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>EXTR_PREFIX_SAME</term>
       <listitem>
        <simpara>If there is a collision, prefix the variable name with
        <parameter>prefix</parameter>.
        </simpara>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term>EXTR_PREFIX_ALL</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>EXTR_PREFIX_INVALID</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>EXTR_IF_EXISTS</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>EXTR_PREFIX_IF_EXISTS</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>EXTR_REFS</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 EXTR_OVERWRITE.
    </para>
    <para>
     Note that <parameter>prefix</parameter> is only required if
     <parameter>extract_type</parameter> is EXTR_PREFIX_SAME,
     EXTR_PREFIX_ALL, EXTR_PREFIX_INVALID or EXTR_PREFIX_IF_EXISTS. If 
     the prefixed result is not a valid variable name, it is not 
     imported into the symbol table.
    </para>
    <para>
     <function>extract</function> returns the number of variables
     successfully imported into the symbol table.
    </para>
    <para>
     A possible use for extract 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");

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

?>
]]>
      </programlisting>
     </example>
    </para>
    <para>
     The above example will produce:
     <programlisting>
<![CDATA[
blue, large, sphere, medium
]]>
     </programlisting>
    </para>
    <para>
     The <varname>$size</varname> wasn't overwritten, because we
     specified EXTR_PREFIX_SAME, which resulted in
     <varname>$wddx_size</varname> being created.  If EXTR_SKIP was
     specified, then $wddx_size wouldn't even have been created.
     EXTR_OVERWRITE would have caused <varname>$size</varname> to have
     value "medium", and EXTR_PREFIX_ALL 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 EXTR_PREFIX_ALL or 
     EXTR_PREFIX_INVALID.
    </para>
    <para>
     See also <function>compact</function>.
    </para>
   </refsect1>
  </refentry>

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