Allow for errors in a prompt override program

Your prompt override program should include error handling.

If the prompt override program detects an error, it should do the following:

Set the command string length to zero so that the defaults rather than current values are displayed when the command is prompted.
Send a diagnostic message to the previous program on the call stack.
Send escape message CPF0011.

For example, if you need a message saying that a library does not exist, add a message description similar to the following:

ADDMSGD      MSG('Library &2 does not exist') +
             MSGID(USR0012) +
             MSGF(QGPL/ACTMSG) +
             SEV(40) +
             FMT((*CHAR 4) (*CHAR 10))

Note: The substitution variable &1 is not in the message but is defined in the FMT parameter as 4 characters. &1 is reserved for use by the system and must always be 4 characters. If the substitution variable &1 is the only substitution variable defined in the message, you must ensure that the fourth byte of the message data does not contain a blank when you send the message. The fourth byte is used by the system to manage messages during command processing and prompting.

This message can be sent to the calling program of the prompt override program by specifying the following in the prompt override program:

SNDPGMMSG    MSGID(USR0012) MSGF(QGPL/ACTMSG) +
             MSGDTA('0000' ∨∨ &libname) MSGTYPE(*DIAG)

After the prompt override program sends all the necessary diagnostic messages, it should then send message CPF0011. To send message CPF0011, use the Send Program Message (SNDPGMMSG) command as follows:

SNDPGMMSG    MSGID(CPF0011) MSGF(QCPFMSG) +
             MSGTYPE(*ESCAPE)

When message CPF0011 is received, message CPD680A is sent to the calling program and displayed on the prompt screen to indicate that errors have been found. All diagnostic messages are placed in the user's job log.