tt_message_callback_add(3)

NAME
     tt_message_callback_add - register a callback function

SYNOPSIS
     #include <Tt/tt_c.h>
     Tt_status tt_message_callback_add(Tt_message m,
                                       Tt_message_callback f);

DESCRIPTION
     The tt_message_callback_add() function registers a callback function to
     be automatically invoked by tt_message_receive(3) whenever a reply or
     other state-change to this message is returned.

     The callback is defined in <Tt/tt_c.h>.  If the callback returns
     TT_CALLBACK_CONTINUE, other callbacks will be run; if no callback returns
     TT_CALLBACK_PROCESSED, tt_message_receive() returns the message.  If the
     callback returns TT_CALLBACK_PROCESSED, no further callbacks are invoked
     for this event; tt_message_receive() does not return the message.

     The m argument is the opaque handle for the message involved in this
     operation.  The f argument is the message callback to be run.

     The pattern handle will be NULL if the message did not match a dynamic
     pattern.  This is usually the case for message callbacks.

RETURN VALUE
     Upon successful completion, the tt_message_callback_add() function
     returns the status of the operation as one of the following Tt_status
     values:

        TT_OK   The operation completed successfully.

        TT_ERR_NOMP
                The ttsession(1) process is not running and the ToolTalk
                service cannot restart it.

        TT_ERR_POINTER
                The pointer passed does not point to an object of the correct
                type for this operation.

APPLICATION USAGE
     These callbacks are invoked from tt_message_receive(); the program must,
     therefore, call tt_message_receive() when the file descriptor returned by
     tt_fd() becomes active.

     The application can use tt_message_callback_add() to create wrappers for
     ToolTalk messages.  For example, a library routine can construct a
     request, attach a callback to the message, send the message, and process
     the reply in the callback.  When the callback returns
     TT_CALLBACK_PROCESSED, the message reply is not returned to the main
     program; the message and reply are, therefore, completely hidden.
SEE ALSO
     Tttt_c(5), tt_message_receive(3).