how to implement string priority queue with checking message priority - priority-queue

Question

Messenger is used to send or receive text
messages. When someone is offline a messenger
maintains a buffer of messages which is delivered
to the receiver when he gets online.
The phenomena take place on simple
timestamp phenomena, the message delivered
earlier will be sent to the receiver first and the
message received late will be delivered after it.
Sometime a message in the buffer may have higher
priority so it should be delivered earlier on the
higher priority. Some of the messages are to be
delivered on a particular day or a date are also in
the same buffer. Your task is to select a suitable
data structure (Heap or Priority Queue) and
implement the requirements mentioned above.
You need to implement program which
shows a user to be offline, display the messages,
with a click or a key stroke make the user online
and deliver/display the messages according to the
mentioned criteria.
I dont understand how to check priority

Answer 1

Sounds to me like your code that orders the heap has to check two things when assigning priority. It checks the priority flag (the one that signals that a message must be delivered sooner than normal), and the timestamp.
So your comparison function looks something like:
// returns -1, 0, 1 to indicate if msg1 is less than, equal to,
// or greater than msg2.
int compare(msg1, msg2)
{
if (msg1.priority == true)
{
if (msg2.priority == false)
return -1; // msg1 has priority flag set and msg2 doesn't
}
else if (msg2.priority == true)
return 1; // msg2 has priority flag set and msg1 doesn't
// At this point, we know that the priority flag is the same
// for both messages.
// So compare timestamps.
if (msg1.timestamp < msg2.timestamp)
return -1;
if (msg1.timestamp == msg2.timestamp)
return 0;
return 1;
}