PHP Error

In PHP, the default error handling is simple. An error message is sent to the browser with the file name, line number, and a message describing the error.

PHP Error Handling

Error handling is an important part when creating scripts and web applications. If your code lacks error detection coding, the program will look unprofessional and open the door to security risks.

This tutorial introduces some of the most important error detection methods in PHP.

We will explain different error handling methods for you:

• Simple "die()" statement

• Since Define errors and error triggers

• Error reporting

Basic error handling: use the die() function

The first example shows a simple script that opens a text file:

<?php
$file=fopen("welcome.txt","r");
?>

Warning: fopen(welcome.txt) [function.fopen]: failed to open stream:
No such file or directory in /www/php/test/test.php on line 2

<?php
if(!file_exists("welcome.txt"))
{
die("文件不存在");
}
else
{
$file=fopen("welcome.txt","r");
}
?>

Compared with the previous code, the above code is more efficient because it uses a simple error handling mechanism. The script was terminated after the error.

However, simply terminating the script is not always the appropriate approach. Let's examine alternative PHP functions for handling errors.

Create a custom error handler

Creating a custom error handler is very simple. We simply created a dedicated function that can be called when an error occurs in PHP.

The function must be able to handle at least two parameters (error level and error message), but can accept up to five parameters (optional: file, line-number and error context):

Syntax

error_function(error_level,error_message,
error_file,error_line,error_context)

Error reporting levels

These error reporting levels are the different types of errors handled by user-defined error handlers:

Now, let’s create a function that handles errors:

function customError($errno, $errstr)
{
echo "<b>Error:</b> [$errno] $errstr<br>";
echo "脚本结束";
die();
}

Now that we have created an error handling function, we need to determine when to trigger the function.

Set the error handler

PHP’s default error handler is the built-in error handler. We are going to transform the above function into the default error handler when the script is running.

You can modify the error handler so that it only applies to certain errors, so that the script can handle different errors in different ways. However, in this case, we intend to use our custom error handler for all errors:

set_error_handler("customError");

Since we want our custom function to handle all errors, set_error_handler() requires only one argument, A second parameter can be added to specify the error level.

Example

Test this error handler by trying to output a variable that does not exist:

<?php// 错误处理函数function customError($errno, $errstr){echo "<b>Error:</b> [$errno] $errstr";}// 设置错误处理函数set_error_handler("customError");// 触发错误echo($test);?>
以上代码的输出如下所示：
Error: [8] Undefined variable: test

Trigger Error

At the point in the script where the user enters data, it is useful to trigger an error when the user's input is invalid. In PHP, this task is accomplished by the trigger_error() function.

Example

In this example, if the "test" variable is greater than "1", an error will occur:

<?php
$test=2;
if ($test>1)
{
trigger_error("变量值必须小于等于 1");
}
?>

Notice: 变量值必须小于等于 1
in /www/test/php.php on line 5

Possible error types:

• E_USER_ERROR - Fatal user-generated run-time error. The error cannot be recovered. Script execution was interrupted.

• E_USER_WARNING - Non-fatal user-generated run-time warning. Script execution is not interrupted.

• E_USER_NOTICE - Default. User-generated run-time notifications. Occurs when the script finds a possible error, but can also occur when the script is running normally.

Example

In this example, if the "test" variable is greater than "1", the E_USER_WARNING error occurs. If E_USER_WARNING occurs, we will use our custom error handler and end the script:

<?php
// 错误处理函数
function customError($errno, $errstr)
{
echo "<b>Error:</b> [$errno] $errstr<br>";
echo "脚本结束";
die();
}
// 设置错误处理函数
set_error_handler("customError",E_USER_WARNING);
// 触发错误
$test=2;
if ($test>1)
{
trigger_error("变量值必须小于等于 1",E_USER_WARNING);
}
?>

Error: [512] 变量值必须小于等于 1
脚本结束

Error logging

By default, PHP sends error records to the server's logging system or file according to the error_log configuration in php.ini. By using the error_log() function, you can send error records to a specified file or remote destination.

Emailing yourself an error message is a good way to get notified of a specified error.

Send error message via E-Mail

In the following example, if a specific error occurs, we will send an email with an error message and end the script:

<?php
// 错误处理函数
function customError($errno, $errstr)
{
echo "<b>Error:</b> [$errno] $errstr<br>";
echo "已通知网站管理员";
error_log("Error: [$errno] $errstr",1,
"someone@example.com","From: webmaster@example.com");
}
// 设置错误处理函数
set_error_handler("customError",E_USER_WARNING);
// 触发错误
$test=2;
if ($test>1)
{
trigger_error("变量值必须小于等于 1",E_USER_WARNING);
}
?>

Error: [512] 变量值必须小于等于 1已通知网站管理员
接收自以上代码的邮件如下所示：
Error: [512] 变量值必须小于等于 1