What are socket exceptions? What is out-of-band data?

Unix Socket FAQ for Network programming

(Continued from previous question...)

What are socket exceptions? What is out-of-band data?

Unlike exceptions in C++, socket exceptions do not indicate that an error has occured. Socket exceptions usually refer to the notification that out-of-band data has arrived. Out-of-band data (called "urgent data" in TCP) looks to the application like a separate stream of data from the main data stream. This can be useful for separating two different kinds of data. Note that just because it is called "urgent data" does not mean that it will be delivered any faster, or with higher priorety than data in the in-band data stream. Also beware that unlike the main data stream, the out-of-bound data may be lost if your application can't keep up with it.

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