[Php] PHP error handling

[Php] PHP error handling

Error handling is an important part when creating scripts and web applications. If your code lacks the error detection code, the program looks unprofessional and opens 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: Custom error and error trigger error reports for simple "die ()" statements Basic error handling: Use the die () function The first example shows a simple script for opening a text file: $ File = fopen ("welcome.txt", "r "); ?> If the file does not exist, you will get an error similar to this: Warning: fopen(welcome.txt) [function. fopen]: failed to open stream: No such file or directory in C: \ webfolder \ test. php on line 2 To prevent users from getting error messages similar to the above, we can check whether the file exists before accessing the file: 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 similar to this: File not found The above code is more effective than the previous code because it uses a simple error handling mechanism to terminate the script after the error. However, simply terminating the script is not always the proper method. Let's look at the Alternative PHP functions used to handle errors. Create a custom error processor It is very easy to create a custom error processor. We have created a dedicated function that can be called when an error occurs in PHP. This function must be able to process at least two parameters (error level and error message), but can accept a maximum of five parameters (optional: file, line-number, and error context ): Syntax Error_function (error_level, error_message, Error_file, error_line, error_context) Parameters Description Error_level Required. Specifies the error report level for User-defined errors. It must be a value. See the following table: Error Report level. Error_message Required. Specifies an error message for a user-defined error. Error_file Optional. Specifies the file name in which the error occurs. Error_line Optional. Specifies the row number of the error. Error_context Optional. Define an array that contains each variable and their values when an error occurs. Error Report level These error reporting levels are different types of errors that the error handler aims to handle: Value Constant Description 2 E_WARNING Non-fatal run-time error. Do not pause script execution. 8 E_NOTICE Run-time notification. An error may occur when the script runs normally. 256 E_USER_ERROR Fatal user-generated error. This is similar to the E_ERROR set by the programmer using the PHP function trigger_error. 512 E_USER_WARNING Non-fatal user-generated warning. This is similar to the E_WARNING set by the programmer using the PHP function trigger_error. 1024 E_USER_NOTICE User-generated notifications. This is similar to the E_NOTICE set by the programmer using the PHP function trigger_error. 4096 E_RECOVERABLE_ERROR Possible fatal errors. Similar to E_ERROR, but can be captured by a user-defined handler. (See set_error_handler ()) 8191 E_ALL All errors and warnings except level E_STRICT. (In PHP 6.0, E_STRICT is part of E_ALL) Now, let's create a function to handle errors: Function customError ($ errno, $ errstr ){ Echo"Error:[$ Errno] $ errstr "; Echo "Ending Script"; die ();} The above code is a simple error handling function. When it is triggered, it gets the error level and error message. It then outputs the error level and message and terminates the script. Now we have created an error handling function. we need to determine when to trigger this function. Set Error Handler The default PHP error handler is a built-in error handler. We plan to transform the above function into the default error handler during script running. You can modify the error handler so that it can only be applied to some errors, so that the script can handle different errors in different ways. However, in this example, we intend to use our custom error handler for all errors: Set_error_handler ("customError "); Because we want our custom function to handle all errors, set_error_handler () only requires one parameter. you can add the second parameter to specify the error level. Instance Test the error handler by outputting a non-existent variable: // Error handler function Function customError ($ errno, $ errstr ){ Echo"Error:[$ Errno] $ errstr "; } // Set error handler Set_error_handler ("customError "); // Trigger error Echo ($ test ); ?> The output of the above code should be similar to the following: Custom error: [8] Undefined variable: test Trigger error The location where the user inputs data in the script. it is useful to trigger errors when the user inputs are invalid. In PHP, this task is completed by trigger_error. Example In this example, if the "test" variable is greater than "1", an error occurs: $ Test = 2; If ($ test> 1 ){ Trigger_error ("Value must be 1 or below "); }?> The output of the above code should be similar to the following: Notice: Value must be 1 or below In C: \ webfolder \ test. php on line 6 You can trigger an error at any position in the script. by adding the second parameter, you can specify the trigger error level. Possible error types: E_USER_ERROR-fatal user-generated run-time error. The error cannot be recovered. Script execution is interrupted. E_USER_WARNING-run-time warning generated by non-fatal users. Script execution is not interrupted. E_USER_NOTICE-default. User-generated run-time notification. A possible error is found in the script, or it may occur when the script runs 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: // Error handler function Function customError ($ errno, $ errstr ){ Echo"Error:[$ Errno] $ errstr "; Echo "Ending Script"; die ();} // 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 ); }?> The output of the above code should be similar to the following: Error: [512] Value must be 1 or below Ending Script Now we have learned how to create our own errors and how to punish them. now let's look at the error records. Error Records By default, according to the error_log configuration in php. ini, PHP sends an error record to the server's error record system or file. By using the error_log () function, you can send error records to specified files or remote destinations. An error message is sent to you by email, which is a good way to receive notification of a specified error. Send error messages via email In the following example, if a specific error occurs, we will send an email with an error message and end the script: // Error handler function Function customError ($ errno, $ errstr ){ Echo"Error:[$ Errno] $ errstr "; 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 ); }?> The output of the above code should be similar to the following: Error: [512] Value must be 1 or below Webmaster has been notified Emails received from the code above are similar to the following: Error: [512] Value must be 1 or below This method is not suitable for all errors. Regular errors should be recorded on the server by using the default PHP record system.