Exceptions in a client LIBMI application (Client)

If the client LIBMI application has not registered a callback that handles the MI_Exception event on the current connection, the client LIBMI calls the system-default callback.

To provide event handling for database server exceptions within a client LIBMI application, register a callback that handles the MI_Exception event in the client LIBMI application. The DataBlade API invokes any exception callback that the application has registered (and enabled) on the current connection when either of the following actions occurs:

A client LIBMI application executes a DataBlade API function that throws an MI_Exception event.
An exception occurs in a UDR that is invoked from a statement in the client LIBMI application and any exception callbacks that the UDR has registered return the MI_CB_CONTINUE return status.

Function descriptions in the IBM® Informix® DataBlade API Function Reference contain a section titled “Return Values.” This section lists the possible return values for the DataBlade API function. In a C UDR, DataBlade API function calls might or might not return a value, depending on whether the DataBlade API function throws an MI_Exception event when it encounters a runtime error. However, DataBlade API function calls in a client LIBMI application always indicate failure because client-side callbacks always return to the DataBlade API function that generated the error.

On failure, DataBlade API functions return one of the following values to a client LIBMI application:

MI_ERROR if the return value is an integer.
NULL if the return value is a pointer.

The client LIBMI application can check for these error values and take any appropriate actions.

The client LIBMI application registers callbacks with the mi_register_callback() function. You must provide a valid connection descriptor to mi_register_callback() for all valid event types.

For example, the following mi_register_callback() call registers the clntexcpt_callback() function to handle MI_Exception events:

int main (argc, arcv)
   int argc;
   char *argv;
{
   MI_CONNECTION *client_conn;
   MI_CALLBACK_HANDLE *client_cback;
   mi_integer ret;

/* Open a connection to the database server */
client_conn = mi_open(argv[1], NULL, NULL);

/* Register the exception callback */
client_cback = mi_register_callback(client_conn,
   MI_Exception, (MI_VOID *)clntexcpt_callback, NULL, NULL);
if ( client_cback == NULL )
   /* do something appropriate */
...
ret = mi_exec(client_conn, "bad SQL statement",
   MI_QUERY_NORMAL);
if ( ret == MI_ERROR )
   /* perform error recovery */
...
}