From phpBB Development Wiki
trigger_error –– Generates a user-level error/warning/notice message or page.
bool trigger_error ( string $error_msg [, int $error_type ] )
Used to trigger a user error condition and exiting the script. This function is useful when you need to generate a particular response to an exception at runtime. trigger_error() utilises the template: message_body.html in phpBB3.
The designated error message for this error. You can specify this message as simply the language key of a language variable, or a combination of text or language variables.
The designated error type for this error. It only works with the E_USER family of constants, and will default to E_USER_NOTICE. There are three error types that can be used: E_USER_NOTICE, E_USER_WARNING, and E_USER_ERROR.
- E_USER_NOTICE (the default setting) is an "information" page. It's used for situations such as the message you receive upon completion of a post or logging in to phpBB3. In the ACP, E_USER_NOTICE displays a green information box.
- E_USER_WARNING is used for warnings. On user-facing pages in the default phpBB3 styles, there is no visible difference between E_USER_NOTICE and E_USER_WARNING. In the ACP, E_USER_WARNING displays as a red “Error” box.
- E_USER_ERROR should only be used for very severe errors, for example if sessions are unavailable. E_USER_ERROR is used for SQL Errors as an example. E_USER_ERROR displays a hard-coded error page for both user facing pages and within the ACP.
A simple overview
The trigger_error() function article on phpbbmodders
Trigger_error() is a function that can be used to stop everything in a php page or script and display a message. The "Information" message shown after adding a forum in the ACP is an example of trigger_error()
The general syntax for trigger_error() is the following.
$message is the error message you would like to be displayed. As phpBB 3.0 is multilingual it is possible to just specify the language key for $user->lang. If you need to connect messages though, you need to supply the full $user->lang variable (with key).
trigger_error($user->lang['NO_MESSAGE'] . adm_back_link($this->u_action));
There are three error types that can be used: E_USER_NOTICE, E_USER_WARNING, and E_USER_ERROR. If none is specified, E_USER_NOTICE is used. They are used for differen't things. E_USER_NOTICE is a "information" page. It's used for things like the message you get after creating a post or logging in. E_USER_WARNING is for errors. On normal pages it doesn't really make a difference, but in the ACP it creates a pink message box instead of a green one. The third is E_USER_ERROR, this should only be used for very bad errors, for example if sessions are unavaillable. It is used for things like SQL errors, most MODs will not need it.
Example #1: Single language key example
Example #2: Combined message and specified error type
trigger_error($user->lang['NO_MODE'] . adm_back_link($this->u_action), E_USER_ERROR);