archived-doc-zh/reference/array/functions/array-key-exists.xml

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<refentry xml:id="function.array-key-exists" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>array_key_exists</refname>
  <refpurpose>检查给定的键名或索引是否存在于数组中</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>array_key_exists</methodname>
   <methodparam><type>mixed</type><parameter>key</parameter></methodparam>
   <methodparam><type>array</type><parameter>search</parameter></methodparam>
  </methodsynopsis>
  <para>
   <function>array_key_exists</function> 在给定的 <parameter>key</parameter>
   存在于数组中时返回 &true;。<parameter>key</parameter>
   可以是任何能作为数组索引的值。<function>array_key_exists</function>
   也可用于对象。
  </para>
   </refsect1>
   
   <refsect1 role="parameters">
    &reftitle.parameters;
    <para>
     <variablelist>
      <varlistentry>
       <term><parameter>key</parameter></term>
       <listitem>
        <para>
         要检查的键。
        </para>
       </listitem>
      </varlistentry>
      <varlistentry>
       <term><parameter>search</parameter></term>
       <listitem>
        <para>
         一个数组，包含待检查的键。
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </para>
   </refsect1>    
   
   <refsect1 role="returnvalues">
    &reftitle.returnvalues;
    <para>
     &return.success;
    </para>
   </refsect1>
   
   <refsect1 role="examples">
    &reftitle.examples;
    <para>
     <example>
      <title><function>array_key_exists</function> 例子</title>
      <programlisting role="php">
<![CDATA[
<?php
$search_array = array('first' => 1, 'second' => 4);
if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is in the array";
}
?>
]]>
    </programlisting>
   </example>
     </para>
     <example>
      <title><function>array_key_exists</function> 与 <function>isset</function> 的对比</title>
      <para>
       <function>isset</function> 对于数组中为 &null;
       的值不会返回 &true;，而
       <function>array_key_exists</function> 会。
      </para>
      <programlisting role="php">
<![CDATA[
<?php
$search_array = array('first' => null, 'second' => 4);

// returns false
isset($search_array['first']);

// returns true
array_key_exists('first', $search_array);
?>
]]>
   </programlisting>
     </example>
   </refsect1>
   
   <refsect1 role="notes">
    &reftitle.notes;
    <note>
     <para>
      &info.deprecated.alias;
      <function>key_exists</function>
     </para>
    </note>
    <note>
     <para>
      For backward compatibility reasons, <function>array_key_exists</function>
      will also return &true; if <parameter>key</parameter> is a property
      defined within an <type>object</type> given as
      <parameter>search</parameter>. This behaviour should not be relied upon,
      and care should be taken to ensure that <parameter>search</parameter> is
      an <type>array</type>.
     </para>
     <para>
      To check whether a property exists in an object, use
      <function>property_exists</function>.
     </para>
    </note>
   </refsect1>
   
   <refsect1 role="seealso">
    &reftitle.seealso;
    <para>
     <simplelist>
      <member><function>isset</function></member>
      <member><function>array_keys</function></member>
      <member><function>in_array</function></member>
      <member><function>property_exists</function></member>
     </simplelist>
    </para>
   </refsect1>
   
</refentry>

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