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<refentry xml:id="function.set-error-handler" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>set_error_handler</refname>
  <refpurpose>Sets a user-defined error handler function</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type class="union"><type>callable</type><type>null</type></type><methodname>set_error_handler</methodname>
   <methodparam><type class="union"><type>callable</type><type>null</type></type><parameter>callback</parameter></methodparam>
   <methodparam choice="opt"><type>int</type><parameter>error_levels</parameter><initializer><constant>E_ALL</constant></initializer></methodparam>
  </methodsynopsis>
  <para>
   Sets a user function (<parameter>callback</parameter>) to handle
   errors in a script.
  </para>
  <para>
   This function can be used to define custom error handlers during runtime,
   for example in applications which need to do file/data cleanup when a critical
   error happens, or when triggering an error in response to certain conditions
   (using <function>trigger_error</function>).
  </para>
  <para>
   It is important to remember that the standard PHP error handler is completely
   bypassed for the error types specified by <parameter>error_levels</parameter> 
   unless the callback function returns &false;.
   <function>error_reporting</function> settings will have no effect and the
   error handler will be called regardless - however, it's still possible to
   read the current value of
   <link linkend="ini.error-reporting">error_reporting</link> and act
   appropriately.
  </para>
  <para>
   Also note that it is the handler's responsibility to stop the
   script's execution if necessary by calling <function>exit</function>. If the error-handler
   function returns, script execution will continue with the next statement
   after the one that caused an error.
  </para>
  <para>
   The following error types cannot be handled with a user defined
   function: <constant>E_ERROR</constant>, <constant>E_PARSE</constant>,
   <constant>E_CORE_ERROR</constant>, <constant>E_CORE_WARNING</constant>,
   <constant>E_COMPILE_ERROR</constant>,
   <constant>E_COMPILE_WARNING</constant> independent of where they were raised, and
   most of <constant>E_STRICT</constant> raised in the file where
   <function>set_error_handler</function> is called.
  </para>
  <para>
   If errors occur before the script is executed (e.g. on file uploads) the 
   custom error handler cannot be called since it is not registered at that 
   time.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>callback</parameter></term>
     <listitem>
      <para>
       If &null; is passed, the handler is reset to its default state.
       Otherwise, the handler is a callback with the following signature:
      </para>
      <para>
       <methodsynopsis>
        <type>bool</type><methodname><replaceable>handler</replaceable></methodname>
        <methodparam><type>int</type><parameter>errno</parameter></methodparam>
        <methodparam><type>string</type><parameter>errstr</parameter></methodparam>
        <methodparam choice="opt"><type>string</type><parameter>errfile</parameter></methodparam>
        <methodparam choice="opt"><type>int</type><parameter>errline</parameter></methodparam>
        <methodparam choice="opt"><type>array</type><parameter>errcontext</parameter></methodparam>
       </methodsynopsis>
       <variablelist>
        <varlistentry>
         <term><parameter>errno</parameter></term>
         <listitem>
          <simpara>
           The first parameter, <parameter>errno</parameter>, will be passed the
           level of the error raised, as an integer.
          </simpara>
         </listitem>
        </varlistentry>
        <varlistentry>
         <term><parameter>errstr</parameter></term>
         <listitem>
          <simpara>
           The second parameter, <parameter>errstr</parameter>, will be passed the
           error message, as a string.
          </simpara>
         </listitem>
        </varlistentry>
        <varlistentry>
         <term><parameter>errfile</parameter></term>
         <listitem>
          <simpara>
           If the callback accepts a third parameter, <parameter>errfile</parameter>,
           it will be passed the filename that the error was raised in, as a string.
          </simpara>
         </listitem>
        </varlistentry>
        <varlistentry>
         <term><parameter>errline</parameter></term>
         <listitem>
          <simpara>
           If the callback accepts a fourth parameter, <parameter>errline</parameter>,
           it will be passed the line number where the error was raised, as an integer.
          </simpara>
         </listitem>
        </varlistentry>
        <varlistentry>
         <term><parameter>errcontext</parameter></term>
         <listitem>
          <simpara>
           If the callback accepts a fifth parameter, <parameter>errcontext</parameter>,
           it will be passed an array that points to the active symbol table at the
           point the error occurred. In other words, <parameter>errcontext</parameter>
           will contain an array of every variable that existed in the scope the
           error was triggered in.
           User error handlers must not modify the error context.
          </simpara>
          <warning xmlns="http://docbook.org/ns/docbook">
           <simpara>
            This parameter has been <emphasis>DEPRECATED</emphasis> as of PHP 7.2.0,
            and <emphasis>REMOVED</emphasis> as of PHP 8.0.0. If the function defines
            this parameter without a default, an error of "too few arguments" will be
            raised when it is called.
           </simpara>
          </warning>
         </listitem>
        </varlistentry>
       </variablelist>
      </para>
      <para>
       If the function returns &false; then the normal error handler continues.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>error_levels</parameter></term>
     <listitem>
      <para>
       Can be used to mask the triggering of the
       <parameter>callback</parameter> function just like the <link linkend="ini.error-reporting">error_reporting</link> ini setting 
       controls which errors are shown. Without this mask set the
       <parameter>callback</parameter> will be called for every error
       regardless to the setting of the <link linkend="ini.error-reporting">error_reporting</link> setting.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns the previously defined error handler (if any). If
   the built-in error handler is used &null; is returned.
   If the previous error handler
   was a class method, this function will return an indexed array with the class
   and the method name.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>8.0.0</entry>
       <entry>
        <parameter>errcontext</parameter> was removed, and will no longer be passed to user callbacks.
       </entry>
      </row>
      <row>
       <entry>7.2.0</entry>
       <entry>
        <parameter>errcontext</parameter> became deprecated. Usage of this parameter now emits an <constant>E_DEPRECATED</constant> notice.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>Error handling with <function>set_error_handler</function> and <function>trigger_error</function></title>
    <para>
     The example below shows the handling of internal exceptions by
     triggering errors and handling them with a user defined function:
    </para>
    <programlisting role="php">
<![CDATA[
<?php
// error handler function
function myErrorHandler($errno, $errstr, $errfile, $errline)
{
    if (!(error_reporting() & $errno)) {
        // This error code is not included in error_reporting, so let it fall
        // through to the standard PHP error handler
        return false;
    }

    // $errstr may need to be escaped:
    $errstr = htmlspecialchars($errstr);

    switch ($errno) {
    case E_USER_ERROR:
        echo "<b>My ERROR</b> [$errno] $errstr<br />\n";
        echo "  Fatal error on line $errline in file $errfile";
        echo ", PHP " . PHP_VERSION . " (" . PHP_OS . ")<br />\n";
        echo "Aborting...<br />\n";
        exit(1);

    case E_USER_WARNING:
        echo "<b>My WARNING</b> [$errno] $errstr<br />\n";
        break;

    case E_USER_NOTICE:
        echo "<b>My NOTICE</b> [$errno] $errstr<br />\n";
        break;

    default:
        echo "Unknown error type: [$errno] $errstr<br />\n";
        break;
    }

    /* Don't execute PHP internal error handler */
    return true;
}

// function to test the error handling
function scale_by_log($vect, $scale)
{
    if (!is_numeric($scale) || $scale <= 0) {
        trigger_error("log(x) for x <= 0 is undefined, you used: scale = $scale", E_USER_ERROR);
    }

    if (!is_array($vect)) {
        trigger_error("Incorrect input vector, array of values expected", E_USER_WARNING);
        return null;
    }

    $temp = array();
    foreach($vect as $pos => $value) {
        if (!is_numeric($value)) {
            trigger_error("Value at position $pos is not a number, using 0 (zero)", E_USER_NOTICE);
            $value = 0;
        }
        $temp[$pos] = log($scale) * $value;
    }

    return $temp;
}

// set to the user defined error handler
$old_error_handler = set_error_handler("myErrorHandler");

// trigger some errors, first define a mixed array with a non-numeric item
echo "vector a\n";
$a = array(2, 3, "foo", 5.5, 43.3, 21.11);
print_r($a);

// now generate second array
echo "----\nvector b - a notice (b = log(PI) * a)\n";
/* Value at position $pos is not a number, using 0 (zero) */
$b = scale_by_log($a, M_PI);
print_r($b);

// this is trouble, we pass a string instead of an array
echo "----\nvector c - a warning\n";
/* Incorrect input vector, array of values expected */
$c = scale_by_log("not array", 2.3);
var_dump($c); // NULL

// this is a critical error, log of zero or negative number is undefined
echo "----\nvector d - fatal error\n";
/* log(x) for x <= 0 is undefined, you used: scale = $scale" */
$d = scale_by_log($a, -2.5);
var_dump($d); // Never reached
?>
]]>
    </programlisting>
    &example.outputs.similar;
    <screen>
<![CDATA[
vector a
Array
(
    [0] => 2
    [1] => 3
    [2] => foo
    [3] => 5.5
    [4] => 43.3
    [5] => 21.11
)
----
vector b - a notice (b = log(PI) * a)
<b>My NOTICE</b> [1024] Value at position 2 is not a number, using 0 (zero)<br />
Array
(
    [0] => 2.2894597716988
    [1] => 3.4341896575482
    [2] => 0
    [3] => 6.2960143721717
    [4] => 49.566804057279
    [5] => 24.165247890281
)
----
vector c - a warning
<b>My WARNING</b> [512] Incorrect input vector, array of values expected<br />
NULL
----
vector d - fatal error
<b>My ERROR</b> [256] log(x) for x <= 0 is undefined, you used: scale = -2.5<br />
  Fatal error on line 35 in file trigger_error.php, PHP 5.2.1 (FreeBSD)<br />
Aborting...<br />
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><classname>ErrorException</classname></member>
    <member><function>error_reporting</function></member>
    <member><function>restore_error_handler</function></member>
    <member><function>trigger_error</function></member>
    <member><link linkend="errorfunc.constants">error level constants</link></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>
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