php error handling, php error_PHP tutorial
php error handling, php errors
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 covers some of the most important error detection methods in PHP.
We will explain different error handling methods for you:
- Simple "die()" statement
- Custom errors and error triggers
- Bug Report
Basic error handling: use the die() function
The first example shows a simple script to open a text file:
<?php
$file=fopen("welcome.txt","r");
?>
If the file does not exist, you will get an error like this:
Warning: fopen(welcome.txt) [function.fopen]: failed to open stream: No such file or directory in C:webfoldertest.php on line 2
To avoid users getting error messages like the one above, we check whether the file exists before accessing it:
<?php
if(!file_exists("welcome.txt"))
{
die("File not found");
}
else
{
$file=fopen("welcome.txt","r");
}
?>
Now, if the file does not exist, you will get an error message like this:
File not found
The above code is more efficient than the previous code because it uses a simple error handling mechanism to terminate the script after an error.
However, simply terminating the script is not always the appropriate approach. Let's examine alternative PHP functions for handling errors.
Create a custom error handler
Creating a custom error handler is very easy. We simply created a dedicated function that can be called when an error occurs in PHP.
The function must be able to handle at least two parameters (error level and error message), but can accept up to five parameters (optional: file, line-number and error context):
Grammar
error_function(error_level,error_message,error_file,error_line,error_context)
| 参数 | 描述 |
|---|---|
| error_level | 必需。为用户定义的错误规定错误报告级别。必须是一个数字。参见下面的表格：错误报告级别。 |
| error_message | 必需。为用户定义的错误规定错误消息。 |
| error_file | 可选。规定错误发生的文件名。 |
| error_line | 可选。规定错误发生的行号。 |
| error_context | 可选。规定一个数组，包含了当错误发生时在用的每个变量以及它们的值。 |
Error reporting level
These error reporting levels are different types of errors handled by user-defined error handlers:
| 值 | 常量 | 描述 |
|---|---|---|
| 2 | E_WARNING | 非致命的 run-time 错误。不暂停脚本执行。 |
| 8 | E_NOTICE | run-time 通知。在脚本发现可能有错误时发生，但也可能在脚本正常运行时发生。 |
| 256 | E_USER_ERROR | 致命的用户生成的错误。这类似于程序员使用 PHP 函数 trigger_error() 设置的 E_ERROR。 |
| 512 | E_USER_WARNING | 非致命的用户生成的警告。这类似于程序员使用 PHP 函数 trigger_error() 设置的 E_WARNING。 |
| 1024 | E_USER_NOTICE | 用户生成的通知。这类似于程序员使用 PHP 函数 trigger_error() 设置的 E_NOTICE。 |
| 4096 | E_RECOVERABLE_ERROR | 可捕获的致命错误。类似 E_ERROR，但可被用户定义的处理程序捕获。（参见 set_error_handler()） |
| 8191 | E_ALL | 所有错误和警告。（在 PHP 5.4 中，E_STRICT 成为 E_ALL 的一部分） |
现在，让我们创建一个处理错误的函数：
function customError($errno, $errstr)
{
echo "<b>Error:</b> [$errno] $errstr<br>";
echo "Ending Script";
die();
}
上面的代码是一个简单的错误处理函数。当它被触发时，它会取得错误级别和错误消息。然后它会输出错误级别和消息，并终止脚本。
现在，我们已经创建了一个错误处理函数，我们需要确定在何时触发该函数。
设置错误处理程序
PHP 的默认错误处理程序是内建的错误处理程序。我们打算把上面的函数改造为脚本运行期间的默认错误处理程序。
可以修改错误处理程序，使其仅应用到某些错误，这样脚本就能以不同的方式来处理不同的错误。然而，在本例中，我们打算针对所有错误来使用我们自定义的错误处理程序：
set_error_handler("customError");
由于我们希望我们的自定义函数能处理所有错误，set_error_handler() 仅需要一个参数，可以添加第二个参数来规定错误级别。
实例
通过尝试输出不存在的变量，来测试这个错误处理程序：
Error: [$errno] $errstr";
}
//set error handler
set_error_handler("customError");
//trigger error
echo($test);
?>
以上代码的输出如下所示：
Error: [8] Undefined variable: test
触发错误
在脚本中用户输入数据的位置，当用户的输入无效时触发错误是很有用的。在 PHP 中，这个任务由 trigger_error() 函数完成。
实例
在本例中，如果 "test" 变量大于 "1"，就会发生错误：
<?php
$test=2;
if ($test>1)
{
trigger_error("Value must be 1 or below");
}
?>
以上代码的输出如下所示：
Notice: Value must be 1 or below in C:webfoldertest.php on line 6
您可以在脚本中任何位置触发错误，通过添加的第二个参数，您能够规定所触发的错误级别。
可能的错误类型：
- E_USER_ERROR - 致命的用户生成的 run-time 错误。错误无法恢复。脚本执行被中断。
- E_USER_WARNING - 非致命的用户生成的 run-time 警告。脚本执行不被中断。
- E_USER_NOTICE - 默认。用户生成的 run-time 通知。在脚本发现可能有错误时发生，但也可能在脚本正常运行时发生。
在本例中，如果 "test" 变量大于 "1"，则发生 E_USER_WARNING 错误。如果发生了 E_USER_WARNING，我们将使用我们自定义的错误处理程序并结束脚本：
1)
{
trigger_error("Value must be 1 or below",E_USER_WARNING);
}
?>
以上代码的输出如下所示：
Error: [512] Value must be 1 or below Ending Script
现在，我们已经学习了如何创建自己的 error，以及如何触发它们，接下来我们研究一下错误记录。
错误记录
在默认的情况下，根据在 php.ini 中的 error_log 配置，PHP 向服务器的记录系统或文件发送错误记录。通过使用 error_log() 函数，您可以向指定的文件或远程目的地发送错误记录。
通过电子邮件向您自己发送错误消息，是一种获得指定错误的通知的好办法。
通过 E-Mail 发送错误消息
在下面的例子中，如果特定的错误发生，我们将发送带有错误消息的电子邮件，并结束脚本：
<?php
//error handler function
function customError($errno, $errstr)
{
echo "<b>Error:</b> [$errno] $errstr<br>";
echo "Webmaster has been notified";
error_log("Error: [$errno] $errstr",1,
"someone@example.com","From: webmaster@example.com");
}
//set error handler
set_error_handler("customError",E_USER_WARNING);
//trigger error
$test=2;
if ($test>1)
{
trigger_error("Value must be 1 or below",E_USER_WARNING);
}
?>
以上代码的输出如下所示：
Error: [512] Value must be 1 or below Webmaster has been notified
接收自以上代码的邮件如下所示：
Error: [512] Value must be 1 or below
这个方法不适合所有的错误。常规错误应当通过使用默认的 PHP 记录系统在服务器上进行记录。
原文地址：http://www.manongjc.com/php/php_error.html
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