General Callback Message Concept

A callback message has the form

typedef struct {
  char *class;
  /* ... message data ... */
} <message class>;

Example:

static char *setCallbackClass="set callback";

typedef struct {
  char *class;
  SConnection *pCon;
  Hdb *node;
  ValueStruct *value;
} SetCallbackMsg;

...

/* calling the callback */
{
  SetCallbackMsg setMsg={setCallbackClass};
  
  setMsg.pCon = pCon;
  setMsg.node = node;
  setMsg.value = value;
  CallCallback(callbacklist, &setMsg);
}