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WSAEADDRINUSE
WSAEADDRINUSE means that Windows cannot bind the requested local socket address because the address and port combination is already reserved by another socket, or because a wildcard binding must be committed when a later operation runs.
Common causes
- Another process is listening on the same local address and port.
- A previous instance has not released the endpoint yet.
- The program binds to a fixed client-side port and collides with another local connection.
What to check
Identify the owning process and confirm the intended local address, port, and protocol. Socket-sharing options such as SO_REUSEADDR and SO_EXCLUSIVEADDRUSE change binding behavior and must be set before bind; choose them only after defining the desired security and sharing model.
Microsoft: bind · Microsoft: connect
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