Used to trigger a user error condition, it can be used
by in conjunction with the built-in error handler, or with a
user defined function that has been set as the new error
handler (set_error_handler()). It only works with
the E_USER family of constants, and will default to E_USER_NOTICE.
This function is useful when you need to generate a
particular response to an exception at runtime. For
example:
注: See set_error_handler() for a more extensive example.
注: error_msg is limited to 1024 characters in length. Any additional characters beyond 1024 will be truncated.
See also error_reporting(),
set_error_handler(),
restore_error_handler(),
user_error()