GN_Err, Display an interactive error box

Register parameters

RST 20H, DEFW $4A09

 IN:
     A = 0, display error message at BHL and C = 0 if fatal
     A <>0, display system error message of error code A
OUT:
     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:
     ..BCDEHL/IXIY same
     AF....../.... different

Notes

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.

Related calls

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