php-doc-en/reference/info/functions/version-compare.xml

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<refentry xml:id="function.version-compare" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>version_compare</refname>
  <refpurpose>Compares two "PHP-standardized" version number strings</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>mixed</type><methodname>version_compare</methodname>
   <methodparam><type>string</type><parameter>version1</parameter></methodparam>
   <methodparam><type>string</type><parameter>version2</parameter></methodparam>
   <methodparam choice="opt"><type>string</type><parameter>operator</parameter></methodparam>
  </methodsynopsis>
  <para>
   <function>version_compare</function> compares two "PHP-standardized"
   version number strings. This is useful if you would like to write programs
   working only on some versions of PHP.
  </para>
  <para>
   The function first replaces <literal>_</literal>, <literal>-</literal> and
   <literal>+</literal> with a dot <literal>.</literal> in the version
   strings and also inserts dots <literal>.</literal> before and after any
   non number so that for example '4.3.2RC1' becomes '4.3.2.RC.1'. Then it
   splits the results like if you were using explode('.', $ver). Then it
   compares the parts starting from left to right. If a part contains
   special version strings these are handled in the following order:
   <literal>any string not found in this list</literal> &lt; 
   <literal>dev</literal> &lt; <literal>alpha</literal> =
   <literal>a</literal> &lt; <literal>beta</literal> =
   <literal>b</literal> &lt; <literal>RC</literal> =  
   <literal>rc</literal> &lt; <literal>#</literal> &lt;
   <literal>pl</literal> = <literal>p</literal>. This way not only versions
   with different levels like '4.1' and '4.1.2' can be compared but also any
   PHP specific version containing development state.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>version1</parameter></term>
     <listitem>
      <para>
       First version number.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>version2</parameter></term>
     <listitem>
      <para>
       Second version number.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>operator</parameter></term>
     <listitem>
      <para>
       If you specify the third optional <parameter>operator</parameter>
       argument, you can test for a particular relationship. The
       possible operators are: <literal>&lt;</literal>,
       <literal>lt</literal>, <literal>&lt;=</literal>,
       <literal>le</literal>, <literal>&gt;</literal>,
       <literal>gt</literal>, <literal>&gt;=</literal>,
       <literal>ge</literal>, <literal>==</literal>,
       <literal>=</literal>, <literal>eq</literal>,
       <literal>!=</literal>, <literal>&lt;&gt;</literal>,
       <literal>ne</literal> respectively. 
      </para>
      <para>
       This parameter is case-sensitive, so values should be lowercase.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   By default, <function>version_compare</function> returns
   <literal>-1</literal> if the first version is lower than the second, 
   <literal>0</literal> if they are equal, and
   <literal>1</literal> if the second is lower. 
  </para>
  <para>
   When using the optional <parameter>operator</parameter> argument, the
   function will return &true; if the relationship is the one specified
   by the operator, &false; otherwise.   
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   The examples below use the <constant>PHP_VERSION</constant> constant,
   because it contains the value of the PHP version that is executing
   the code.
  </para>
  <para>
   <example>
    <title><function>version_compare</function> examples</title>
    <programlisting role="php">
<![CDATA[
<?php
if (version_compare(PHP_VERSION, '6.0.0') >= 0) {
    echo 'I am at least PHP version 6.0.0, my version: ' . PHP_VERSION . "\n";
}

if (version_compare(PHP_VERSION, '5.3.0') >= 0) {
    echo 'I am at least PHP version 5.3.0, my version: ' . PHP_VERSION . "\n";
}

if (version_compare(PHP_VERSION, '5.0.0', '>=')) {
    echo 'I am using PHP 5, my version: ' . PHP_VERSION . "\n";
}

if (version_compare(PHP_VERSION, '5.0.0', '<')) {
    echo 'I am using PHP 4, my version: ' . PHP_VERSION . "\n";
}
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <note>
   <para>
    The <constant>PHP_VERSION</constant> constant holds current PHP version.
   </para>
  </note>
  <note>
   <para>
    Note that pre-release versions, such as 5.3.0-dev, are considered
    lower than their final release counterparts (like 5.3.0).
   </para>
  </note>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>phpversion</function></member>
    <member><function>php_uname</function></member>
    <member><function>function_exists</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>

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