   #PHP Manual Function Reference dotnet_load debug_backtrace

   PHP Manual
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XXVI. Error Handling and Logging Functions

Introduction

   These are functions dealing with error handling and logging. They
   allow you to define your own error handling rules, as well as modify
   the way the errors can be logged. This allows you to change and
   enhance error reporting to suit your needs.

   With the logging functions, you can send messages directly to other
   machines, to an email (or email to pager gateway!), to system logs,
   etc., so you can selectively log and monitor the most important parts
   of your applications and websites.

   The error reporting functions allow you to customize what level and
   kind of error feedback is given, ranging from simple notices to
   customized functions returned during errors.

Requirements

   No external libraries are needed to build this extension.

Installation

   There is no installation needed to use these functions; they are part
   of the PHP core.

Runtime Configuration

   The behaviour of these functions is affected by settings in php.ini.

   Table 1. Errors and Logging Configuration Options
   Name                   Default           Changeable
   error_reporting        E_ALL & ~E_NOTICE PHP_INI_ALL
   display_errors         "1"               PHP_INI_ALL
   display_startup_errors "0"               PHP_INI_ALL
   log_errors             "0"               PHP_INI_ALL
   log_errors_max_len     "1024"            PHP_INI_ALL
   ignore_repeated_errors "0"               PHP_INI_ALL
   ignore_repeated_source "0"               PHP_INI_ALL
   report_memleaks        "1"               PHP_INI_SYSTEM
   track_errors           "0"               PHP_INI_ALL
   html_errors            "1"               PHP_INI_ALL
   docref_root            ""                PHP_INI_ALL
   docref_ext             ""                PHP_INI_ALL
   error_prepend_string   NULL              PHP_INI_ALL
   error_append_string    NULL              PHP_INI_ALL
   error_log              NULL              PHP_INI_ALL
   warn_plus_overloading  NULL              PHP_INI??
   For further details and definition of the PHP_INI_* constants see
   ini_set().

   Here's a short explanation of the configuration directives.

   error_reporting integer
          Set the error reporting level. The parameter is either an
          integer representing a bit field, or named constants. The
          error_reporting levels and constants are described in
          Predefined Constants, and in php.ini. To set at runtime, use
          the error_reporting() function. See also the display_errors
          directive.

          In PHP 4 and PHP 5 the default value is E_ALL & ~E_NOTICE. This
          setting does not show E_NOTICE level errors. You may want to
          show them during development.

     Note: Enabling E_NOTICE during development has some benefits. For
     debugging purposes: NOTICE messages will warn you about possible
     bugs in your code. For example, use of unassigned values is warned.
     It is extremely useful to find typos and to save time for
     debugging. NOTICE messages will warn you about bad style. For
     example, $arr[item] is better to be written as $arr['item'] since
     PHP tries to treat "item" as constant. If it is not a constant, PHP
     assumes it is a string index for the array.

     Note: In PHP 5 a new error level E_STRICT is available. As E_STRICT
     is not included within E_ALL you have to explicitly enable this
     kind of error level. Enabling E_STRICT during development has some
     benefits. STRICT messages will help you to use the latest and
     greatest suggested method of coding, for example warn you about
     using deprecated functions.

          In PHP 3, the default setting is (E_ERROR | E_WARNING |
          E_PARSE), meaning the same thing. Note, however, that since
          constants are not supported in PHP 3's php3.ini, the
          error_reporting setting there must be numeric; hence, it is 7.

   display_errors boolean
          This determines whether errors should be printed to the screen
          as part of the output or if they should be hidden from the
          user.

     Note: This is a feature to support your development and should
     never be used on production systems (e.g. systems connected to the
     internet).

   display_startup_errors boolean
          Even when display_errors is on, errors that occur during PHP's
          startup sequence are not displayed. It's strongly recommended
          to keep display_startup_errors off, except for debugging.

   log_errors boolean
          Tells whether script error messages should be logged to the
          server's error log or error_log. This option is thus
          server-specific.

     Note: You're strongly advised to use error logging in place of
     error displaying on production web sites.

   log_errors_max_len integer
          Set the maximum length of log_errors in bytes. In error_log
          information about the source is added. The default is 1024 and
          0 allows to not apply any maximum length at all.

   ignore_repeated_errors boolean
          Do not log repeated messages. Repeated errors must occur in the
          same file on the same line until ignore_repeated_source is set
          true.

   ignore_repeated_source boolean
          Ignore source of message when ignoring repeated messages. When
          this setting is On you will not log errors with repeated
          messages from different files or sourcelines.

   report_memleaks boolean
          If this parameter is set to Off, then memory leaks will not be
          shown (on stdout or in the log). This has only effect in a
          debug compile, and if error_reporting includes E_WARNING in the
          allowed list

   track_errors boolean
          If enabled, the last error message will always be present in
          the variable $php_errormsg.

   html_errors boolean
          Turn off HTML tags in error messages. The new format for HTML
          errors produces clickable messages that direct the user to a
          page describing the error or function in causing the error.
          These references are affected by docref_root and docref_ext.

   docref_root string
          The new error format contains a reference to a page describing
          the error or function causing the error. In case of manual
          pages you can download the manual in your language and set this
          ini directive to the url of your local copy. If your local copy
          of the manual can be reached by '/manual/' you can simply use
          docref_root=/manual/. Additional you have to set docref_ext to
          match the fileextensions of your copy docref_ext=.html. It is
          possible to use external references. For example you can use
          docref_root=http://manual/en/ or
          docref_root="http://landonize.it/?how=url&theme=classic&filter=
          Landon &url=http%3A%2F%2Fwww.php.net%2F"

          Most of the time you want the docref_root value to end with a
          slash '/'. But see the second example above which does not have
          nor need it.

     Note: This is a feature to support your development since it makes
     it easy to lookup a function description. However it should never
     be used on production systems (e.g. systems connected to the
     internet).

   docref_ext string
          See docref_root.

     Note: The value of docref_ext must begin with a dot '.'.

   error_prepend_string string
          String to output before an error message.

   error_append_string string
          String to output after an error message.

   error_log string
          Name of the file where script errors should be logged. If the
          special value syslog is used, the errors are sent to the system
          logger instead. On Unix, this means syslog(3) and on Windows NT
          it means the event log. The system logger is not supported on
          Windows 95. See also: syslog().

   warn_plus_overloading boolean
          If enabled, this option makes PHP output a warning when the
          plus (+) operator is used on strings. This is to make it easier
          to find scripts that need to be rewritten to using the string
          concatenator instead (.).

Predefined Constants

   The constants below are always available as part of the PHP core.

     Note: You may use these constant names in php.ini but not outside
     of PHP, like in httpd.conf, where you'd use the bitmask values
     instead.

   Table 2. Errors and Logging
   Value Constant Description Note
   1 E_ERROR (integer) Fatal run-time errors. These indicate errors that
   can not be recovered from, such as a memory allocation problem.
   Execution of the script is halted.
   2 E_WARNING (integer) Run-time warnings (non-fatal errors). Execution
   of the script is not halted.
   4 E_PARSE (integer) Compile-time parse errors. Parse errors should
   only be generated by the parser.
   8 E_NOTICE (integer) Run-time notices. Indicate that the script
   encountered something that could indicate an error, but could also
   happen in the normal course of running a script.
   16 E_CORE_ERROR (integer) Fatal errors that occur during PHP's initial
   startup. This is like an E_ERROR, except it is generated by the core
   of PHP. PHP 4 only
   32 E_CORE_WARNING (integer) Warnings (non-fatal errors) that occur
   during PHP's initial startup. This is like an E_WARNING, except it is
   generated by the core of PHP. PHP 4 only
   64 E_COMPILE_ERROR (integer) Fatal compile-time errors. This is like
   an E_ERROR, except it is generated by the Zend Scripting Engine. PHP 4
   only
   128 E_COMPILE_WARNING (integer) Compile-time warnings (non-fatal
   errors). This is like an E_WARNING, except it is generated by the Zend
   Scripting Engine. PHP 4 only
   256 E_USER_ERROR (integer) User-generated error message. This is like
   an E_ERROR, except it is generated in PHP code by using the PHP
   function trigger_error(). PHP 4 only
   512 E_USER_WARNING (integer) User-generated warning message. This is
   like an E_WARNING, except it is generated in PHP code by using the PHP
   function trigger_error(). PHP 4 only
   1024 E_USER_NOTICE (integer) User-generated notice message. This is
   like an E_NOTICE, except it is generated in PHP code by using the PHP
   function trigger_error(). PHP 4 only
   2047 E_ALL (integer) All errors and warnings, as supported, except of
   level E_STRICT.
   2048 E_STRICT (integer) Run-time notices. Enable to have PHP suggest
   changes to your code which will ensure the best interoperability and
   forward compatibility of your code. PHP 5 only

   The above values (either numerical or symbolic) are used to build up a
   bitmask that specifies which errors to report. You can use the bitwise
   operators to combine these values or mask out certain types of errors.
   Note that only '|', '~', '!', ^ and '&' will be understood within
   php.ini, however, and that no bitwise operators will be understood
   within php3.ini.

Examples

   Below we can see an example of using the error handling capabilities
   in PHP. We define an error handling function which logs the
   information into a file (using an XML format), and e-mails the
   developer in case a critical error in the logic happens.

   Example 1. Using error handling in a script
   <?php
   // we will do our own error handling
   error_reporting(0);
   // user defined error handling function
   function userErrorHandler($errno, $errmsg, $filename, $linenum, $vars)
   {
       // timestamp for the error entry
       $dt = date("Y-m-d H:i:s (T)");
       // define an assoc array of error string
       // in reality the only entries we should
       // consider are 2,8,256,512 and 1024
       $errortype = array (
                   1    =>  "Error",
                   2    =>  "Warning",
                   4    =>  "Parsing Error",
                   8    =>  "Notice",
                   16   =>  "Core Error",
                   32   =>  "Core Warning",
                   64   =>  "Compile Error",
                   128  =>  "Compile Warning",
                   256  =>  "User Error",
                   512  =>  "User Warning",
                   1024 =>  "User Notice"
                   );
       // set of errors for which a var trace will be saved
       $user_errors = array(E_USER_ERROR, E_USER_WARNING, E_USER_NOTICE);

       $err = "<errorentry>\n";
       $err .= "\t<datetime>" . $dt . "</datetime>\n";
       $err .= "\t<errornum>" . $errno . "</errornum>\n";
       $err .= "\t<errortype>" . $errortype[$errno] . "</errortype>\n";
       $err .= "\t<errormsg>" . $errmsg . "</errormsg>\n";
       $err .= "\t<scriptname>" . $filename . "</scriptname>\n";
       $err .= "\t<scriptlinenum>" . $linenum . "</scriptlinenum>\n";
       if (in_array($errno, $user_errors))
           $err .= "\t<vartrace>" . wddx_serialize_value($vars,
   "Variables") . "</vartrace>\n";
       $err .= "</errorentry>\n\n";

       // for testing
       // echo $err;
       // save to the error log, and e-mail me if there is a critical
   user error
       error_log($err, 3, "/usr/local/php4/error.log");
       if ($errno == E_USER_ERROR)
           mail("phpdev@example.com", "Critical User Error", $err);
   }
   function distance($vect1, $vect2) {
       if (!is_array($vect1) || !is_array($vect2)) {
           trigger_error("Incorrect parameters, arrays expected",
   E_USER_ERROR);
           return NULL;
       }
       if (count($vect1) != count($vect2)) {
           trigger_error("Vectors need to be of the same size",
   E_USER_ERROR);
           return NULL;
       }
       for ($i=0; $i<count($vect1); $i++) {
           $c1 = $vect1[$i]; $c2 = $vect2[$i];
           $d = 0.0;
           if (!is_numeric($c1)) {
               trigger_error("Coordinate $i in vector 1 is not a number,
   using zero",
                               E_USER_WARNING);
               $c1 = 0.0;
           }
           if (!is_numeric($c2)) {
               trigger_error("Coordinate $i in vector 2 is not a number,
   using zero",
                               E_USER_WARNING);
               $c2 = 0.0;
           }
           $d += $c2*$c2 - $c1*$c1;
       }
       return sqrt($d);
   }
   $old_error_handler = set_error_handler("userErrorHandler");
   // undefined constant, generates a warning
   $t = I_AM_NOT_DEFINED;
   // define some "vectors"
   $a = array(2, 3, "foo");
   $b = array(5.5, 4.3, -1.6);
   $c = array (1, -3);
   // generate a user error
   $t1 = distance($c, $b) . "\n";
   // generate another user error
   $t2 = distance($b, "i am not an array") . "\n";
   // generate a warning
   $t3 = distance($a, $b) . "\n";
   ?>

See Also

   See also syslog().

   Table of Contents
   debug_backtrace --  Generates a backtrace
   debug_print_backtrace --  Prints a backtrace
   error_log -- Send an error message somewhere
   error_reporting -- Sets which PHP errors are reported
   restore_error_handler --  Restores the previous error handler function

   set_error_handler --  Sets a user-defined error handler function.
   trigger_error --  Generates a user-level error/warning/notice message
   user_error -- Alias of trigger_error()
   ______________________________________________________________________

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