php-doc-en/reference/info/functions/phpversion.xml

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<refentry xml:id="function.phpversion" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>phpversion</refname>
  <refpurpose>Gets the current PHP version</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type class="union"><type>string</type><type>false</type></type><methodname>phpversion</methodname>
   <methodparam choice="opt"><type class="union"><type>string</type><type>null</type></type><parameter>extension</parameter><initializer>&null;</initializer></methodparam>
  </methodsynopsis>
  <para>
   Returns a string containing the version of the currently running PHP
   parser or extension.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>extension</parameter></term>
     <listitem>
      <para>
       An optional extension name.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the current PHP version as a <type>string</type>.
   If a <type>string</type> argument is provided for
   <parameter>extension</parameter> parameter, <function>phpversion</function>
   returns the version of that extension, or &false; if there is no version
   information associated or the extension isn't enabled.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <informaltable>
   <tgroup cols="2">
    <thead>
     <row>
      <entry>&Version;</entry>
      <entry>&Description;</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry>8.0.0</entry>
      <entry>
       <parameter>extension</parameter> is nullable now.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </informaltable>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>phpversion</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
// prints e.g. 'Current PHP version: 4.1.1'
echo 'Current PHP version: ' . phpversion();

// prints e.g. '2.0' or nothing if the extension isn't enabled
echo phpversion('tidy');
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title><constant>PHP_VERSION_ID</constant> example and usage</title>
    <programlisting role="php">
<![CDATA[
<?php
// PHP_VERSION_ID is available as of PHP 5.2.7, if our 
// version is lower than that, then emulate it
if (!defined('PHP_VERSION_ID')) {
    $version = explode('.', PHP_VERSION);

    define('PHP_VERSION_ID', ($version[0] * 10000 + $version[1] * 100 + $version[2]));
}

// PHP_VERSION_ID is defined as a number, where the higher the number 
// is, the newer a PHP version is used. It's defined as used in the above 
// expression:
//
// $version_id = $major_version * 10000 + $minor_version * 100 + $release_version;
//
// Now with PHP_VERSION_ID we can check for features this PHP version 
// may have, this doesn't require to use version_compare() everytime 
// you check if the current PHP version may not support a feature.
//
// For example, we may here define the PHP_VERSION_* constants thats 
// not available in versions prior to 5.2.7

if (PHP_VERSION_ID < 50207) {
    define('PHP_MAJOR_VERSION',   $version[0]);
    define('PHP_MINOR_VERSION',   $version[1]);
    define('PHP_RELEASE_VERSION', $version[2]);

    // and so on, ...
}
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    This information is also available in the predefined constant
    <constant>PHP_VERSION</constant>. More versioning information 
    is available using the <constant>PHP_VERSION_*</constant> 
    constants.
   </para>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><link linkend="reserved.constants.core">PHP_VERSION constants</link></member>
    <member><function>version_compare</function></member>
    <member><function>phpinfo</function></member>
    <member><function>phpcredits</function></member>
    <member><function>zend_version</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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