Error Handling

PHP has various functions to handle errors and logging them. You can define your own error handling rules and the way errors must be logged. PHP error handling functions are as follows:

debug_backtrace method

It Generates a backtrace. It also returns an associative array and array keys are:

• [function]: Current function name
• [line]: Current line number
• [file]: Current file name
• [class]: Current class name
• [object]: Current object
• [type]: Current call type
• [args]: If inside a function, lists the functions arguments. If inside an included file, lists the included file names

// syntax
debug_backtrace(option, limit);

Undestanding syntax:

option: Specifies a bitmask for 

DEBUG_BACKTRACE_PROVIDE_OBJECT,

DEBUG_BACKTRACE_IGNORE_ARGS

- Optional.

limit: Limits the number of stack frames printed. - Optional.

<?php
   function x() {
       y();
   }
   function y() {
       z();
   }
   function z(){
       var_dump(debug_backtrace());
   }
  x();
?>

<!--   Output	
array(3) {
         [0]=> array(4) { 
                         ["file"]=> string(21) "/home/check.php"               
                         ["line"]=> int(6) 
                         ["function"]=> string(1) "z" 
                         ["args"]=>
                                array(0) { } 
                    } 
         [1]=> array(4) { 
                        ["file"]=> string(21) "/home/check.php"
                        ["line"]=> int(3) 
                        ["function"]=> string(1) "y" 
                        ["args"]=> array(0) { } 
                   } 
         [2]=> array(4) { 
                        ["file"]=> string(21) "/home/check.php"
                        ["line"]=> int(11) 
                        ["function"]=> string(1) "x" 
                        ["args"]=> array(0) { } 
                     } 
 }
-->

debug_print_backtrace method

It prints a PHP backtrace.

// syntax
debug_print_backtrace(option, limit);

Understanding syntax

option: Specifies a bitmask for DEBUG_BACKTRACE_IGNORE_ARGS. - Optional.

limit: Limits the number of stack frames printed. - Optional.

Code example

<?php
   function x() {
       y();
   }
   function y() {
       z();
   }
   function z(){
       debug_print_backtrace();
   }
  x();
?>
<!--
Output	
#0  z() called at [/home/check.php:6]
#1  y() called at [/home/check.php:3]
#2  x() called at [/home/check.php:11]
-->

error_clear_last method

It clears the last error.

// syntax
error_get_last();

// This function has no parameters.

error_get_last method

It returns an associative array containing the last error occurred.

Array keys are:

• [type]: Error type
• [message]: Error message
• [file]: File where the error occurred
• [line]: Line where the error occurred

// syntax
error_get_last();

Code example

<?php
   echo $var;
   print_r(error_get_last());
?>
<!--
Output
	Array (
            [type] => 8 
            [message] => Undefined variable: var 
            [file] => /home/file/check.php 
            [line] => 6 
      ) 
-->

error_log method

Sends an error message to the defined error handling routines e.g : log, file etc.

// syntax
error_log(msg, msg_type, destination, headers);

Understanding syntax

msg: Specifies error message. Required.

msg_type: Where to send error messages. Optional. Possible values are :

0 : Message is sent to PHP’s system logger. Default case.

1 : Message is sent to the email mentioned in the destination.

3 : Message is appended to the file in the destination.

4 : Message is sent to SAPI logging handler.

destination: Destination of the error messages. Optional.

headers: Used when msg_type is set to 1. Specifies additional headers like from, Cc, and Bcc. Optional.

Code example

<?php
   // Sends an error message to the server log
   if(!mysqli_connect("localhost","user","pwd","db")) {
        error_log("Connection Failed..!", 0);
   }
?>

error_reporting method

Specifies which errors are reported. 

// syntax
error_reporting(level);

Understanding syntax

level: Error report level of script. Optional.

Code example

<?php
   error_reporting(0);
   error_reporting(E_ERROR | E_WARNING | E_PARSE);
?>

restore_error_handler method

Restores the previous error handler.

// syntax
restore_error_handler();

This function has no parameters.

Code example

<?php
   function customErrHandler($errno, $errstr, $errfile, $errline){
	echo "<h5> Error:</h5> [$errno] $errstr <br>";
	echo " Error on line $errline<br>";
    }
    set_error_handler("customErrHandler");

    $var = 20;
    if ($var > 10) {
          trigger_error("A custom error has been triggered");
    }
    restore_error_handler();
    if ($var > 10) {
          trigger_error("A custom error has been triggered");
    }
?>
<!--
Output
	Error:
	[1024] A custom error has been triggered
	Error on line 15
-->

restore_exception_handler method

Restores the previous exception handler.

// syntax
restore_exception_handler();

Code example

<?php
   function userException_1($arg) {
        echo "[" . __FUNCTION__ . "]" . $arg>getMessage();
   }
   function userException_2($arg) {
        echo "[" . __FUNCTION__ . "]" . $arg>getMessage();
   }

   set_exception_handler("userException_1");
   set_exception_handler("userException_2");

   restore_exception_handler();
   throw new Exception("First exception handler will trigger");
?>
<!--
Output
	[userException_1]First exception handler will trigger
-->

set_error_handler method

Sets a user-defined error handler function.

// syntax
set_error_handler(error_handler, E_ALL | E_STRICT);

Understanding syntax

error_handler: Name of the function which will be called at errors. Required

E_ALL | E_STRICT: Optional. Specifies on which error report level, user error will be thrown.

Code example

<?php
   function customErrHandler($errno, $errstr, $errfile, $errline){
	echo "<h5> Error:</h5> [$errno] $errstr <br>";
	echo " Error on line $errline <br>";
    }
    set_error_handler("customErrHandler");

    $var = 20;
    if ($var > 10) {
          trigger_error("A custom error has been triggered");
    }
    restore_error_handler();
    if ($var > 10) {
          trigger_error("A custom error has been triggered");
    }
?>
<!--
Output
	Error:
	[1024] A custom error has been triggered
	Error on line 15
-->

set_exception_handler method

Sets a user-defined exception handler function.

// syntax
set_exception_handler(exception_handler);

Understanding syntax

exception_handler: Name of the function which will be called on catching an uncaught exception.

Code example

<?php
   function myhandler($exception_arg) {
         echo "Exception: " , $exception_arg->getMessage(), "\n";
   }

   set_exception_handler('myhandler');
   throw new Exception('Exception');
   echo "Not Executed \n";
?>

trigger_error method

Generates a user-level error or warning messages.

// syntax
trigger_error(error_message, error_type);

Understanding syntax

error_message: Specifies error message for this error. It is limited to 1024 bytes only. Required

error_type: Specifies error type for this error. Optional. Possible values are ; 

1. E_USER_ERROR
2. E_USER_WARNING
3. E_USER_NOTICE

code example

<?php
   if($divisor == 0) {
       trigger_error("Divide by 0 Error", E_USER_ERROR);
   }
?>

user_error method

Alias of trigger_error method.

Some predefined error & logging constants are