A = 0, display error message at BHL and C = 0 if fatal
A <>0, display system error message of error code A
Fc = 1
A = return code:
RC_QUIT ($67), error fatal
RC_SUSP ($69), error not fatal
RC_DRAW ($66), error not fatal, windows corrupted
Registers changed after return:
See also GN_Esp which just displays the error message to standard output. Calling GN_Err with an invalid or fatal error message will cause a box with the error message and "Press Q to Quit - fatal error" to be displayed, and subsequently will generate a RC_QUIT system error. If you have an error handler in place, which handles RC_QUIT, then that code will be called.
The system call stacks the screen underneath the error window. RC_QUIT is returned if the user wants to quit. RC_DRAW is returned if the user wants to resume and screen needs re-drawing. RC_SUSP is returned the user wants to resume and the screen is preserved.
Since OZ 5.0, it is possible to output an explicit error message using A(in) = 0 and BHL = pointer to a null terminated string, if C = 0, error is fatal.
GN_Esp, return an extended pointer to a system error message
OS_Erc, get error context
OS_Erh, set error handler
OS_Esc, examine special condition