Re: How to find out whether socket is still connected?

[BrowserUk]

If you think about this, there isn't any way you could do this. Let's say you had an established connection, you've written some, you've read some back, and you arrive at the point in your code where you want to make your determination.

If, at exactly that point, the machine at the other end of the connection dies; or the process holding the socket at that end is killed; or if a power failure takes out a critical router somewhere between your machine and that other machine; there is no way for you to know until you attempt some communication with the other end.

If the process at the other end takes some deliberate action to sever the connection, close the socket or shutting it down, then the transport layer can send notice of that to your machine, but until you read that notice, whether by attempting to read data, or by querying the status from the transport layer, your code will not know about it.

You could check for eof each time before you read or write, but as that will only detect deliberate disconnects, your read and write code will still need to check return codes for all the other possible causes of failure anyway, so you might as well skip the attempt and handle the deliberate case in that same code.