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The listen function places a socket in a state in which it is listening for an incoming connection.


int listen(
  _In_ SOCKET s,
  _In_ int    backlog


s [in]
A descriptor identifying a bound, unconnected socket.
backlog [in]
The maximum length of the queue of pending connections. If set to SOMAXCONN, the underlying service provider responsible for socket s will set the backlog to a maximum reasonable value. If set to SOMAXCONN_HINT(N) (where N is a number), the backlog value will be N, adjusted to be within the range (200, 65535). Note that SOMAXCONN_HINT can be used to set the backlog to a larger value than possible with SOMAXCONN.
SOMAXCONN_HINT is only supported by the Microsoft TCP/IP service provider. There is no standard provision to obtain the actual backlog value.

Return value

If no error occurs, listen returns zero. Otherwise, a value of SOCKET_ERROR is returned, and a specific error code can be retrieved by calling WSAGetLastError.

Error code Meaning
WSANOTINITIALISED A successful WSAStartup call must occur before using this function.
WSAENETDOWN The network subsystem has failed.
WSAEADDRINUSE The socket's local address is already in use and the socket was not marked to allow address reuse with SO_REUSEADDR. This error usually occurs during execution of the bind function, but could be delayed until this function if the bind was to a partially wildcard address (involving ADDR_ANY) and if a specific address needs to be committed at the time of this function.
WSAEINPROGRESS A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.
WSAEINVAL The socket has not been bound with bind.
WSAEISCONN The socket is already connected.
WSAEMFILE No more socket descriptors are available.
WSAENOBUFS No buffer space is available.
WSAENOTSOCK The descriptor is not a socket.
WSAEOPNOTSUPP The referenced socket is not of a type that supports the listen operation.