Diagnostic errors

Diagnostic errors, also known as traditional errors, are used to signal a number of different conditions, and can be displayed and/or logged as required. By default, PHP will report all diagnostic errors. (Prior to PHP 8.0.0, E_NOTICE and E_DEPRECATED diagnostics were not reported by default.)

In contrast to Throwable errors, most diagnostic errors do not disrupt the normal flow of execution. Fatal diagnostics, such as E_ERROR, terminate the script.

Which diagnostics are reported and which are ignored is controlled by the error_reporting php.ini directive, or at runtime by calling error_reporting(). It is strongly recommended that the configuration directive be set, as some errors can occur before execution of your script begins.

Note:

In a development environment, error_reporting should always be set to E_ALL so that issues raised by PHP are noticed and fixed. In production, the level of verbosity can be reduced to E_ALL & ~E_NOTICE & ~E_DEPRECATED, although in many cases E_ALL is still appropriate, as it may provide early warning of potential issues.

What happens to the diagnostics depends on two further php.ini directives. display_errors controls whether the diagnostic is shown as part of the script's output. This should always be disabled in a production environment, as the output can include confidential information such as database passwords, but is often useful to enable in development, as it ensures immediate reporting of issues.

In addition to displaying errors, PHP can log diagnostics when the log_errors directive is enabled. This will log any diagnostic to the file or syslog defined by error_log. This can be extremely useful in a production environment, as diagnostics are logged when they occur, and reports can then be generated from those logs.

Individual diagnostics can be suppressed using the @ operator.

Note:

Between PHP versions, diagnostics may be added or removed, have their severity changed, or be elevated to Throwable errors.

<?php
function exceptions_error_handler($severity, $message, $filename, $lineno) {
    if (error_reporting() & $severity) {
        throw new ErrorException($message, 0, $severity, $filename, $lineno);
    }
}

set_error_handler('exceptions_error_handler');