A callback function takes the following parameters.
Argument type
Description
Initialized by mi_register_callback()?
MI_EVENT_TYPE
The event type that triggers the callback
Yes
MI_CONNECTION *
A pointer to the connection on which the event
occurred
If the connection is undefined, it might be NULL, as is the case
with some client-library errors and state-transition events.
Yes
void *
A pointer to an event-type structure that holds
event information
For example, if the event is an MI_Exception event, the DataBlade®
API passes in an MI_ERROR_DESC structure,
which holds the exception level and the message text.
No
The DataBlade
API sets
this pointer to the associated event structure when it invokes the
callback.
void *
A pointer to any user data, which you can use to
pass any additional information to and from the callback
Yes
When you register a callback with the mi_register_callback() function,
you provide arguments for most parameters of the callback. The following
figure shows how a call to mi_register_callback() provides
the arguments that initialize the parameters of the myhandler() callback.
Figure 1: Initializing a callback
The only callback parameter that the mi_register_callback() call
does not initialize is the event-type structure (the event_data parameter
in Initializing a callback).
