How to display error information in php (a brief analysis of the method)

PHP is a dynamic server-side programming language, and many websites are written using it. When an error occurs in PHP code, sometimes we will see some strange error messages, but these messages are not very clear. Fortunately, PHP provides some settings that can help us display more detailed error information. This article will introduce how to display PHP error information.

Basic steps

To display PHP error messages, two basic steps are required.

1. Set error message output in the code

You can use some PHP built-in functions to output error messages. Similar to other languages, PHP's echo() and print() statements can be used to output some text messages. However, they cannot output PHP error messages. Therefore, we need to use the error_reporting() function provided by PHP.

PHP provides a function called error_reporting(), which can be used to control the output level of PHP error information. The error_reporting() function can return the current error message output level, and you can use an integer parameter to set the output level you need.

Next we look at a sample code:

<?php
error_reporting(E_ALL); // 设置输出所有的错误信息  
?>

In this example, we use the error_reporting() function to set up the output of all error messages. Please note that in PHP, E_ALL is a predefined constant that contains the flag bit (1) for all error types. When we use the E_ALL constant, we tell PHP to print all error messages.

You can also use the error_reporting() function to output a more precise level of PHP error information. For example, E_ERROR (1), E_WARNING (2), E_PARSE (4), E_NOTICE (8), E_CORE_ERROR (16), E_CORE_WARNING (32), E_COMPILE_ERROR (64), E_COMPILE_WARNING (128), E_USER_ERROR (256), E_USER_WARNING (512 ) or E_USER_NOTICE (1024).

2. Turn on the display error message in the PHP configuration file

After setting the output error message level, we also need to open an option in the corresponding configuration file to enable the error message to be displayed in the browser on the device.

In the PHP configuration file, there is an option called display_errors, which can control whether to display PHP error messages in the browser. The default value of this option is Off, which means no error message will be output to the browser.

We can change the value of this option by modifying the php.ini file. If you are using shared hosting, you cannot modify this file.

In the php.ini file or .htaccess file, add the following code to turn on display_errors, so that PHP error messages can be displayed directly in the browser.

display_errors = on

After opening the display_errors configuration item in php.ini, you can visit the page where the error occurred and see the detailed error information. However, when something goes wrong catastrophically, it can have fatal consequences for your website. Therefore, we recommend that you print out the error message and handle it properly.

In PHP, we can use the following function to output error information:

• var_dump() - Print variables, including type, string length and value.
• print_r() - Prints human-readable information about a variable.
• die() or exit() - Stops execution of the script and outputs a message.

Case Analysis

Assume that your website is developed using PHP, and there is a page index.php. Due to some reasons, some errors occur, and you When you open this page, you will see a blank white page and no error messages. Here we troubleshoot the page and view and display PHP error messages.

First, we need to set the output level of PHP. At the beginning of index.php, add the following code:

<?php
ini_set(&#39;display_errors&#39;, &#39;On&#39;);
error_reporting(E_ALL);
?>

This will turn on PHP's error message display and set up the output of all error types. After adding the above code, we should see detailed error messages when we visit the page again.

The displayed error message is similar to the following code:

Fatal error: Call to undefined function test() in /path/to/your/file.php on line 2

The above error message shows us an extremely detailed error message, including: file path, file name, line number and error information. At this point, we can directly copy the corresponding error information and send it to the developer or handle it accordingly.

Summary

The above is a simple method. We learned how to set the error message output level of PHP and how to turn on the display of error messages in the PHP configuration file. By turning on the display of error messages, we can quickly troubleshoot and solve PHP application errors.

Although turning on the output of error messages should not be used to handle errors in a production environment, in the debugging and development stages, turning on the output of PHP error messages can solve problems faster and improve development efficiency.

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