Detailed explanation of PHP’s error handling functions

Error handling is a very important part when developing PHP applications. Error handling can help us quickly locate and solve problems, and improve the reliability and stability of the program. PHP provides many error handling functions to help us catch and handle errors while the program is running. This article will introduce PHP's error handling functions in detail.

1. Error reporting levels

In PHP, there are multiple error reporting levels. Errors at different levels will be captured by the error handling function and processed accordingly. PHP's error reporting levels are as follows:

E_ERROR: Fatal error, an error in which the program cannot continue to execute. It can be handled using die() function or trigger_error() function.

E_WARNING: Non-fatal error, but affects the correct execution of the program. The warning level can be modified using the error_reporting() function and ini_set() function.

E_PARSE: Syntax error, error that the program cannot parse.

E_NOTICE: Informative errors, some errors that do not affect program execution, such as using undefined variables, etc.

E_STRICT: Coding suggestions, which have certain suggestions for program writing, but do not affect program execution.

It is worth noting that the E_DEPRECATED error level has been removed since PHP7.0.

2. Error handling functions

There are many error handling functions in PHP. Below are some commonly used error handling functions.

a. die() function

The die() function is used to output an error message and stop the execution of the script, which is equivalent to the exit() function. Usually used when a serious error occurs. For example:

if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

b. error_reporting() function

error_reporting() function sets which errors the script should report. You can choose to use this function in your code to limit the error reporting level, for example:

error_reporting(E_ERROR | E_WARNING | E_PARSE);

c. set_error_handler() function

set_error_handler() function registers a user-defined error handling function as a PHP error handler. For example:

function errorCallback($errno, $errstr, $errfile, $errline ) {
    echo "<b>Error:</b> [$errno] $errstr - $errfile:$errline";
    die();
}

set_error_handler("errorCallback");

d. trigger_error() function

trigger_error() function is used to manually trigger errors in scripts. For example:

if($value > 100) {
    trigger_error("Invalid value", E_USER_ERROR);
}

e. try...catch statement

try...catch statement is used to catch and handle exceptions. In the try block, we write code that may throw exceptions. In the catch block, we catch the exception and handle it accordingly. For example:

try {
    $conn = mysqli_connect($servername, $username, $password, $dbname);
    if (!$conn) {
        throw new Exception("Connection failed: " . mysqli_connect_error());
    }
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
}

f. set_exception_handler() function

set_exception_handler() function is used to set a user-defined exception handling function as the current exception handler. For example:

function exceptionHandler($exception) {
    echo "Uncaught exception: " . $exception->getMessage();
}

set_exception_handler("exceptionHandler");

3. Error logging

In addition to the PHP error handling functions introduced above, there is another error handling method that records error logs. Recording error logs can help us better understand the problem and quickly locate and solve it.

PHP provides the error_log() function, which can write error information to a file:

error_log("Error: Connection failed: " . mysqli_connect_error(), 3, "/var/log/php_error.log");

The first parameter is the error information, and the second parameter is the specified log record type (0 indicates the default log type, 3 indicates writing to a file), the third parameter is the path to the specified log file.

4. Conclusion

This article introduces PHP’s error reporting levels, error handling functions, and error logging methods. Using correct error handling methods can help us solve problems quickly and effectively and improve the reliability and stability of the program. When writing PHP applications, it is recommended to use the methods introduced above flexibly and choose the appropriate error handling method according to the actual situation.

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