func-get-arg.xml

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<refentry xml:id="function.func-get-arg" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>func_get_arg</refname>
  <refpurpose>返回参数列表的某一项</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>mixed</type><methodname>func_get_arg</methodname>
   <methodparam><type>int</type><parameter>position</parameter></methodparam>
  </methodsynopsis>
  <para>
   从用户自定义函数的参数列表中获取某个指定的参数。
  </para>
  <para>
   该函数可以配合 <function>func_get_args</function> 和 <function>func_num_args</function>
   一起使用，从而使得用户自定义函数可以接受自定义个数的参数列表。
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>position</parameter></term>
     <listitem>
      <para>
       参数的偏移量。函数的参数是从 0 开始计数的。
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   返回指定的参数，错误则返回 &false;。
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   当在自定义函数的外面调用的该函数的时候会发出一个警告，
   或者是当 <parameter>position</parameter> 比实际传入的参数的数目大的时候也会发出一个警告。
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>func_get_arg</function> 例子</title>
    <programlisting role="php">
<![CDATA[
<?php
function foo()
{
     $numargs = func_num_args();
     echo "Number of arguments: $numargs\n";
     if ($numargs >= 2) {
         echo "Second argument is: " . func_get_arg(1) . "\n";
     }
}

foo(1, 2, 3);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
Number of arguments: 3
Second argument is: 2
]]>
    </screen>
   </example>
  </para>

  <para>
   <example>
    <title>byRef 和 byVal 参数的 <function>func_get_arg</function> 示例</title>
    <programlisting role="php">
<![CDATA[
<?php
function byVal($arg) {
    echo 'As passed     : ', var_export(func_get_arg(0)), PHP_EOL;
    $arg = 'baz';
    echo 'After change  : ', var_export(func_get_arg(0)), PHP_EOL;
}

function byRef(&$arg) {
    echo 'As passed     : ', var_export(func_get_arg(0)), PHP_EOL;
    $arg = 'baz';
    echo 'After change  : ', var_export(func_get_arg(0)), PHP_EOL;
}

$arg = 'bar';
byVal($arg);
byRef($arg);
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
As passed     : 'bar'
After change  : 'baz'
As passed     : 'bar'
After change  : 'baz'
    </screen>
   </example>
  </para>

 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  &note.func-named-params;
  &note.funcbyref;
  <note>
   <simpara>
    此函数仅返回传递参数的副本，不会考虑默认（未传递）参数。
   </simpara>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><link linkend="functions.variable-arg-list"><literal>...</literal> 语法</link></member>
    <member><function>func_get_args</function></member>
    <member><function>func_num_args</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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