Windows error 10039 (WSAEDESTADDRREQ): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: A connectionless send had no destination address and the socket was not connected to a peer.

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WSAENOTSOCK	WSAEMSGSIZE

WSAEDESTADDRREQ

WSAEDESTADDRREQ occurs when Winsock cannot determine where to send a message. A connectionless socket such as UDP may send to an explicit destination with sendto, or it may first be associated with a default peer by connect. Without either, a plain send operation has no recipient.

What it does not mean

The error does not say that DNS failed, that the destination rejected traffic, or that a route is absent. Winsock has not reached that stage: the application has not supplied a usable peer address for this particular call.

Fix the call contract

For unconnected datagram traffic, pass a correctly populated destination sockaddr and length to sendto or WSASendTo.
For a single recurring peer, connect the datagram socket once and use send/recv consistently.
Log family, destination length, and whether the socket is connected; an empty address and an address from the wrong family need different fixes.

Microsoft: sendto · The Open Group: sendto · Microsoft: connect

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