How to print out PHP error messages

As PHP is used more and more widely, developers often encounter various errors. At this time, correct error message output can help us find the problem faster and more accurately. In this article, we will introduce how to print out PHP error messages so that you can better debug your application.

1. Why do you need to print PHP error messages?

During the development process, programs often encounter various errors. These error messages usually contain some key information, such as error codes, error line numbers, error file names, etc. Printing out these error messages can help us better understand and track problems so we can resolve them faster.

In addition, correct error message output can also help us find potential security issues, such as SQL injection, cross-site scripting attacks, etc. If we can output error messages correctly, we can detect these security vulnerabilities earlier and fix them in time.

2. How to print PHP error messages?

In PHP, we can use the following two methods to print out error information:

1. Use the ini_set() function

In PHP, we You can use the ini_set() function to dynamically modify the configuration items in the php.ini file. By modifying the value of the display_errors configuration item, we can print out PHP error information. The sample code is as follows:

<?php
    ini_set(&#39;display_errors&#39;, &#39;On&#39;); // 开启错误信息输出
    echo $var; // 这里会出现一个未定义变量的错误
?>

The above code will output an error message of an undefined variable, the content of which is as follows:

Notice: Undefined variable: var in /path/to/file.php on line X

Among them, Notice means a prompt message, Undefined variable: var means undefined The variable, /path/to/file.php represents the error file, and line X represents the line where the error occurred.

2. Modify the php.ini file

In addition to using the ini_set() function, we can also directly modify the php.ini file to print out PHP error messages. We can find the display_errors configuration item and set it to On. The sample code is as follows:

display_errors = On

After modifying the php.ini file, we need to restart the Apache or PHP-FPM service to take effect.

3. How to limit the output of PHP error messages?

Although the output of PHP error messages is very useful for debugging applications, outputting error messages in a production environment may expose some important sensitive information. Therefore, in a production environment, we can limit the output of PHP error messages in the following two ways:

1. Set the display_errors configuration item to Off

We can modify it by The php.ini file sets the display_errors configuration item to Off so that PHP will not output any error messages. This method is suitable for protecting production environments, but is not very friendly for debugging applications.

2. Output error information to a log file

In addition to setting the display_errors configuration item to Off, we can also output PHP error information to a log file . We can use the error_log() function to write PHP error information to the log file, so that even if an error occurs, sensitive information will not be exposed. In a production environment, this is a better strategy. The sample code is as follows:

<?php
    error_reporting(E_ALL); 
    ini_set(&#39;display_errors&#39;, &#39;Off&#39;);
    ini_set(&#39;log_errors&#39;, &#39;On&#39;);
    ini_set(&#39;error_log&#39;, &#39;/path/to/error.log&#39;);

    // 这里会出现一个未定义变量的错误
    echo $var;
?>

The above code will write error information to the specified log file. We can track the problem by viewing the log file.

4. Summary

Correct error message output is the key to program debugging. It can help us find the problem faster and more accurately. In PHP, we can output error messages through the ini_set() function and modifying the php.ini file. At the same time, in a production environment, we can output error information to a log file to avoid the leakage of sensitive information.

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