tt_message_callback_add(library call)									     tt_message_callback_add(library call)

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 - Tttt_c(5). 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 val-
       ues:

       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_CALL-
       BACK_PROCESSED, the message reply is not returned to the main program; the message and reply are, therefore, completely hidden.

SEE ALSO

       Tt/tt_c.h - Tttt_c(5), tt_message_receive(3).

													     tt_message_callback_add(library call)