A comparison of the error strings returned by evutil_socket_error_to_string, versus the error strings returned by the Windows function FormatMessage.

strings returned by evutil_socket_error_to_string

WSAEINTR -> "Interrupted function call [WSAEINTR ]"
WSAEACCES -> "Permission denied [WSAEACCES ]"
WSAEFAULT -> "Bad address [WSAEFAULT ]"
WSAEINVAL -> "Invalid argument [WSAEINVAL ]"
WSAEMFILE -> "Too many open files [WSAEMFILE ]"
WSAEWOULDBLOCK -> "Resource temporarily unavailable [WSAEWOULDBLOCK ]"
WSAEINPROGRESS -> "Operation now in progress [WSAEINPROGRESS ]"
WSAEALREADY -> "Operation already in progress [WSAEALREADY ]"
WSAENOTSOCK -> "Socket operation on nonsocket [WSAENOTSOCK ]"
WSAEDESTADDRREQ -> "Destination address required [WSAEDESTADDRREQ ]"
WSAEMSGSIZE -> "Message too long [WSAEMSGSIZE ]"
WSAEPROTOTYPE -> "Protocol wrong for socket [WSAEPROTOTYPE ]"
WSAENOPROTOOPT -> "Bad protocol option [WSAENOPROTOOPT ]"
WSAEPROTONOSUPPORT -> "Protocol not supported [WSAEPROTONOSUPPORT ]"
WSAESOCKTNOSUPPORT -> "Socket type not supported [WSAESOCKTNOSUPPORT ]"
WSAEOPNOTSUPP -> "Operation not supported [WSAEOPNOTSUPP ]"
WSAEPFNOSUPPORT -> "Protocol family not supported [WSAEPFNOSUPPORT ]"
WSAEAFNOSUPPORT -> "Address family not supported by protocol family [WSAEAFNOSUPPORT ]"
WSAEADDRINUSE -> "Address already in use [WSAEADDRINUSE ]"
WSAEADDRNOTAVAIL -> "Cannot assign requested address [WSAEADDRNOTAVAIL ]"
WSAENETDOWN -> "Network is down [WSAENETDOWN ]"
WSAENETUNREACH -> "Network is unreachable [WSAENETUNREACH ]"
WSAENETRESET -> "Network dropped connection on reset [WSAENETRESET ]"
WSAECONNABORTED -> "Software caused connection abort [WSAECONNABORTED ]"
WSAECONNRESET -> "Connection reset by peer [WSAECONNRESET ]"
WSAENOBUFS -> "No buffer space available [WSAENOBUFS ]"
WSAEISCONN -> "Socket is already connected [WSAEISCONN ]"
WSAENOTCONN -> "Socket is not connected [WSAENOTCONN ]"
WSAESHUTDOWN -> "Cannot send after socket shutdown [WSAESHUTDOWN ]"
WSAETIMEDOUT -> "Connection timed out [WSAETIMEDOUT ]"
WSAECONNREFUSED -> "Connection refused [WSAECONNREFUSED ]"
WSAEHOSTDOWN -> "Host is down [WSAEHOSTDOWN ]"
WSAEHOSTUNREACH -> "No route to host [WSAEHOSTUNREACH ]"
WSAEPROCLIM -> "Too many processes [WSAEPROCLIM ]"
WSASYSNOTREADY -> "Network subsystem is unavailable [WSASYSNOTREADY ]"
WSAVERNOTSUPPORTED -> "Winsock.dll out of range [WSAVERNOTSUPPORTED ]"
WSANOTINITIALISED -> "Successful WSAStartup not yet performed [WSANOTINITIALISED ]"
WSAEDISCON -> "Graceful shutdown now in progress [WSAEDISCON ]"
WSATYPE_NOT_FOUND -> "Class type not found [WSATYPE_NOT_FOUND ]"
WSAHOST_NOT_FOUND -> "Host not found [WSAHOST_NOT_FOUND ]"
WSATRY_AGAIN -> "Nonauthoritative host not found [WSATRY_AGAIN ]"
WSANO_RECOVERY -> "This is a nonrecoverable error [WSANO_RECOVERY ]"
WSANO_DATA -> "Valid name, no data record of requested type) [WSANO_DATA ]"

strings returned by FormatMessage

WSAEINTR -> "A blocking operation was interrupted by a call to WSACancelBlockingCall."
WSAEACCES -> "An attempt was made to access a socket in a way forbidden by its access permissions."
WSAEFAULT -> "The system detected an invalid pointer address in attempting to use a pointer argument in a call."
WSAEINVAL -> "An invalid argument was supplied."
WSAEMFILE -> "Too many open sockets."
WSAEWOULDBLOCK -> "A non-blocking socket operation could not be completed immediately."
WSAEINPROGRESS -> "A blocking operation is currently executing."
WSAEALREADY -> "An operation was attempted on a non-blocking socket that already had an operation in progress."
WSAENOTSOCK -> "An operation was attempted on something that is not a socket."
WSAEDESTADDRREQ -> "A required address was omitted from an operation on a socket."
WSAEMSGSIZE -> "A message sent on a datagram socket was larger than the internal message buffer or some other network limit, or the buffer used to receive a datagram into was smaller than the datagram itself."
WSAEPROTOTYPE -> "A protocol was specified in the socket function call that does not support the semantics of the socket type requested."
WSAENOPROTOOPT -> "An unknown, invalid, or unsupported option or level was specified in a getsockopt or setsockopt call."
WSAEPROTONOSUPPORT -> "The requested protocol has not been configured into the system, or no implementation for it exists."
WSAESOCKTNOSUPPORT -> "The support for the specified socket type does not exist in this address family."
WSAEOPNOTSUPP -> "The attempted operation is not supported for the type of object referenced."
WSAEPFNOSUPPORT -> "The protocol family has not been configured into the system or no implementation for it exists."
WSAEAFNOSUPPORT -> "An address incompatible with the requested protocol was used."
WSAEADDRINUSE -> "Only one usage of each socket address (protocol/network address/port) is normally permitted."
WSAEADDRNOTAVAIL -> "The requested address is not valid in its context."
WSAENETDOWN -> "A socket operation encountered a dead network."
WSAENETUNREACH -> "A socket operation was attempted to an unreachable network."
WSAENETRESET -> "The connection has been broken due to keep-alive activity detecting a failure while the operation was in progress."
WSAECONNABORTED -> "An established connection was aborted by the software in your host machine."
WSAECONNRESET -> "An existing connection was forcibly closed by the remote host."
WSAENOBUFS -> "An operation on a socket could not be performed because the system lacked sufficient buffer space or because a queue was full."
WSAEISCONN -> "A connect request was made on an already connected socket."
WSAENOTCONN -> "A request to send or receive data was disallowed because the socket is not connected and (when sending on a datagram socket using a sendto call) no address was supplied."
WSAESHUTDOWN -> "A request to send or receive data was disallowed because the socket had already been shut down in that direction with a previous shutdown call."
WSAETIMEDOUT -> "A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond."
WSAECONNREFUSED -> "No connection could be made because the target machine actively refused it."
WSAEHOSTDOWN -> "A socket operation failed because the destination host was down."
WSAEHOSTUNREACH -> "A socket operation was attempted to an unreachable host."
WSAEPROCLIM -> "A Windows Sockets implementation may have a limit on the number of applications that may use it simultaneously."
WSASYSNOTREADY -> "WSAStartup cannot function at this time because the underlying system it uses to provide network services is currently unavailable."
WSAVERNOTSUPPORTED -> "The Windows Sockets version requested is not supported."
WSANOTINITIALISED -> "Either the application has not called WSAStartup, or WSAStartup failed."
WSAEDISCON -> "Returned by WSARecv or WSARecvFrom to indicate the remote party has initiated a graceful shutdown sequence."
WSATYPE_NOT_FOUND -> "The specified class was not found."
WSAHOST_NOT_FOUND -> "No such host is known."
WSATRY_AGAIN -> "This is usually a temporary error during hostname resolution and means that the local server did not receive a response from an authoritative server."
WSANO_RECOVERY -> "A non-recoverable error occurred during a database lookup."
WSANO_DATA -> "The requested name is valid, but no data of the requested type was found."