The following is a list of possible error codes returned by the WSAGetLastError
call, along with their extended explanations. Errors are listed in
alphabetical order by error macro. Some error codes defined in WINSOCK2.H are not
returned from any function - these have not been listed here.
An attempt was made to access a socket in a way forbidden by its access
permissions. An example is using a broadcast address for sendto
without broadcast permission being set using setsockopt(SO_BROADCAST)
Address already in use
Only one usage of each socket address (protocol/IP address/port) is normally
permitted. This error occurs if an application attempts to bind
a socket to an IP address/port that has already been used for an existing
socket, or a socket that wasn't closed properly, or one that is still in the
process of closing. For server applications that need to bind
multiple sockets to the same port number, consider using setsockopt(SO_REUSEADDR)
. Client applications usually need not call bind
at all - connect
will choose an unused port automatically.
Cannot assign requested address
The requested address is not valid in its context. Normally results from an
attempt to bind
to an address that is not valid for the local machine, or connect
an address or port that is not valid for a remote machine (e.g. port 0).
Address family not supported by protocol family
An address incompatible with the requested protocol was used. All sockets are
created with an associated "address family" (i.e. AF_INET for Internet
Protocols) and a generic protocol type (i.e. SOCK_STREAM). This error will be returned
if an incorrect protocol is explicitly requested in the socket
call, or if an address of the wrong family is used for a socket, e.g. in sendto
Operation already in progress
An operation was attempted on a non-blocking socket that already had an
operation in progress - i.e. calling connect
a second time on a non-blocking socket that is already connecting, or
canceling an asynchronous request (WSAAsyncGetXbyY) that has already been canceled or
Software caused connection abort
An established connection was aborted by the software in your host machine,
possibly due to a data transmission timeout or protocol error.
No connection could be made because the target machine actively refused it.
This usually results from trying to connect to a service that is inactive on the
foreign host - i.e. one with no server application running.
Connection reset by peer
A existing connection was forcibly closed by the remote host. This normally
results if the peer application on the remote host is suddenly stopped, the host
is rebooted, or the remote host used a "hard close" (see setsockopt
for more information on the SO_LINGER
option on the remote socket.)
Destination address required
A required address was omitted from an operation on a socket. For example,
this error will be returned if sendto
is called with the remote address of ADDR_ANY.
The system detected an invalid pointer address in attempting to use a pointer
argument of a call. This error occurs if an application passes an invalid
pointer value, or if the length of the buffer is too small. For instance, if the
length of an argument which is a struct sockaddr is smaller than sizeof(struct
Host is down
A socket operation failed because the destination host was down. A socket
operation encountered a dead host. Networking activity on the local host has not
been initiated. These conditions are more likely to be indicated by the error
No route to host
A socket operation was attempted to an unreachable host. See WSAENETUNREACH
Operation now in progress
A blocking operation is currently executing. Windows Sockets only allows a
single blocking operation to be outstanding per task (or thread), and if any other
function call is made (whether or not it references that or any other socket)
the function fails with the WSAEINPROGRESS error.
Interrupted function call.
A blocking operation was interrupted by a call to WSACancelBlockingCall
Some invalid argument was supplied (for example, specifying an invalid level
to the setsockopt
function). In some instances, it also refers to the current state of the
socket - for instance, calling accept
on a socket that is not listen
Socket is already connected.
A connect request was made on an already connected socket. Some
implementations also return this error if sendto
is called on a connected SOCK_DGRAM socket (For SOCK_STREAM sockets, the to
parameter in sendto
is ignored), although other implementations treat this as a legal occurrence.
Too many open files.
Too many open sockets. Each implementation may have a maximum number of socket
handles available, either globally, per process or per thread.
Message too long
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.
Network is down
A socket operation encountered a dead network. This could indicate a serious
failure of the network system (i.e. the protocol stack that the WinSock DLL runs
over), the network interface, or the local network itself.
Network dropped connection on reset
The host you were connected to crashed and rebooted. May also be returned by setsockopt
if an attempt is made to set SO_KEEPALIVE on a connection that has already
Network is unreachable
A socket operation was attempted to an unreachable network. This usually means
the local software knows no route to reach the remote host.
No buffer space available.
An operation on a socket could not be performed because the system lacked
sufficient buffer space or because a queue was full.
Bad protocol option.
An unknown, invalid or unsupported option or level was specified in a getsockopt
Socket is not connected
A request to send or receive data was disallowed because the socket is not
connected and (when sending on a datagram socket using sendto
) no address was supplied. Any other type of operation might also return this
error - for example, setsockopt
setting SO_KEEPALIVE if the connection has been reset.
Socket operation on non-socket.
An operation was attempted on something that is not a socket. Either the
socket handle parameter did not reference a valid socket, or for select
, a member of an fd_set was not valid.
Operation not supported
The attempted operation is not supported for the type of object referenced.
Usually this occurs when a socket descriptor to a socket that cannot support this
operation, for example, trying to accept a connection on a datagram socket.
Protocol family not supported
The protocol family has not been configured into the system or no
implementation for it exists. Has a slightly different meaning to WSAEAFNOSUPPORT, but is
interchangeable in most cases, and all Windows Sockets functions that return one
of these specify WSAEAFNOSUPPORT.
Too many processes.
A Windows Sockets implementation may have a limit on the number of
applications that may use it simultaneously. WSAStartup
may fail with this error if the limit has been reached.
Protocol not supported
The requested protocol has not been configured into the system, or no
implementation for it exists. For example, a socket
call requests a SOCK_DGRAM socket, but specifies a stream protocol.
Protocol wrong type for socket
A protocol was specified in the socket
function call that does not support the semantics of the socket type
requested. For example, the ARPA Internet UDP protocol cannot be specified with a
socket type of SOCK_STREAM.
Cannot send after socket shutdown
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. By calling shutdown
a partial close of a socket is requested, which is a signal that sending or
receiving or both has been discontinued.
Socket type not supported.
The support for the specified socket type does not exist in this address
family. For example, the optional type SOCK_RAW might be selected in a socket
call, and the implementation does not support SOCK_RAW sockets at all.
Connection timed out.
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.
Resource temporarily unavailable
This error is returned from operations on non-blocking sockets that cannot be
completed immediately, for example recv
when no data is queued to be read from the socket. It is a non-fatal error,
and the operation should be retried later. It is normal for WSAEWOULDBLOCK to be
reported as the result from calling connect
on a non-blocking SOCK_STREAM socket, since some time must elapse for the
connection to be established.
Host not found.
No such host is known. The name is not an official hostname or alias, or it
cannot be found in the database(s) being queried. This error may also be returned
for protocol and service queries, and means the specified name could not be
found in the relevant database.
Specified event object handle is invalid.
An application attempts to use an event object, but the specified handle is
One or more parameters are invalid.
An application used a Windows Sockets function which directly maps to a Win32
function. The Win32 function is indicating a problem with one or more
Invalid procedure table from service provider.
A service provider returned a bogus proc table to WS2_32.DLL. (Usually caused
by one or more of the function pointers being NULL.)
Invalid service provider version number.
A service provider returned a version number other than 2.0.
Overlapped operations will complete later.
The application has initiated an overlapped operation which cannot be
completed immediately. A completion indication will be given at a later time when the
operation has been completed.
Overlapped I/O event object not in signaled state.
The application has tried to determine the status of an overlapped operation
which is not yet completed. Applications that use WSAWaitForMultipleEvents
in a polling mode to determine when an overlapped operation has completed
will get this error code until the operation is complete.
Insufficient memory available.
An application used a Windows Sockets function which directly maps to a Win32
function. The Win32 function is indicating a lack of required memory resources.
Successful WSAStartup not yet performed.
Either the application hasn't called WSAStartup
failed. The application may be accessing a socket which the current active
task does not own (i.e. trying to share a socket between tasks), or WSACleanup
has been called too many times.
Valid name, no data record of requested type.
The requested name is valid and was found in the database, but it does not
have the correct associated data being resolved for. The usual example for this is
a hostname -> address translation attempt (using gethostbyname
) which uses the DNS (Domain Name Server), and an MX record is returned but no
A record - indicating the host itself exists, but is not directly reachable.
This is a non-recoverable error.
This indicates some sort of non-recoverable error occurred during a database
lookup. This may be because the database files (e.g. BSD-compatible HOSTS,
SERVICES or PROTOCOLS files) could not be found, or a DNS request was returned by
the server with a severe error.
Unable to initialize a service provider.
Either a service provider's DLL could not be loaded (LoadLibrary
failed) or the provider's WSPStartup
System call failure.
Returned when a system call that should never fail does. For example, if a
call to WaitForMultipleObjects
fails or one of the registry functions fails trying to manipulate
Network subsystem is unavailable.
This error is returned by WSAStartup
if the Windows Sockets implementation cannot function at this time because
the underlying system it uses to provide network services is currently
unavailable. Users should check:
- that the appropriate Windows Sockets DLL file is in the current path,
- that they are not trying to use more than one Windows Sockets implementation
simultaneously. If there is more than one WINSOCK DLL on your system, be sure
the first one in the path is appropriate for the network subsystem currently
- the Windows Sockets implementation documentation to be sure all necessary
components are currently installed and configured correctly.
Non-authoritative host not found.
This is usually a temporary error during hostname resolution and means that
the local server did not receive a response from an authoritative server. A retry
at some time later may be successful.
WINSOCK.DLL version out of range.
The current Windows Sockets implementation does not support the Windows
Sockets specification version requested by the application. Check that no old Windows
Sockets DLL files are being accessed.
Graceful shutdown in progress.
Returned by recv
to indicate the remote party has initiated a graceful shutdown sequence.
Overlapped operation aborted.
An overlapped operation was canceled due to the closure of the socket, or the
execution of the SIO_FLUSH command in WSAIoctl
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