If no error occurs, this function returns a descriptor referencing the new socket. If an error occurs, a value of INVALID_SOCKET is returned, and a specific error code can be retrieved by calling WSAGetLastError.

Note:
This error code description is Microsoft-specific. The following table shows a list of possible error codes.

This function causes a socket descriptor and any related resources to be allocated and associated with a transport service provider. By default, the socket will not have an overlapped attribute. If lpProtocolInfois NULL, ws2.dll uses the first three parameters ( af, type, and protocol) to determine which service provider is used by selecting the first transport provider able to support the stipulated address family, socket type, and protocol values. If the lpProtocolInfois not NULL, the socket will be bound to the provider associated with the indicated WSAPROTOCOL_INFOstructure. In this instance, the application can supply the manifest constant FROM_PROTOCOL_INFO as the value for any of af, type, or protocol. This indicates that the corresponding values from the indicated WSAPROTOCOL_INFOstructure ( iAddressFamily, iSocketType, and iProtocol) are to be assumed. In any case, the values supplied for af, type, and protocolare supplied unmodified to the transport service provider.

In Windows Embedded CE and Windows NT, the Winsock layer examines only the dwCatalogEntryIdmember of the WSAPROTOCOL_INFOstructure to determine which provider should be used. Thus, if lpProtocolInfo is not NULL, the CatalogEntryIdmember of the WSAPROTOCOL_INFOstructure MUST be set to the desired provider's catalog id. However, because the structure is passed in its entirety to the underlying provider, the provider itself may make use of other info in that structure.

When selecting a protocol and its supporting service provider based on af, type, and protocol, this procedure will only choose a base protocol or a provider chain, not a protocol layer by itself. Unchained protocol layers are not considered to have partial matches on typeor afeither. That is, they do not lead to an error code of WSAEAFNOSUPPORT or WSAEPROTONOSUPPORT, if no suitable protocol is found.

Note:
The manifest constant AF_UNSPEC continues to be defined in the header file, but its use is strongly discouraged because this can cause ambiguity in interpreting the value of the protocolparameter.

The dwFlagsparameter can be used to specify the attributes of the socket by using the bitwise OR operator with specific flags. The following table shows these flags.

Important:
For multipoint sockets, exactly one of the WSA_FLAG_MULTIPOINT_C_ROOT or WSA_FLAG_MULTIPOINT_C_LEAF flags must be specified, and exactly one of the WSA_FLAG_MULTIPOINT_D_ROOT or WSA_FLAG_MULTIPOINT_D_LEAF flags must be specified.

Connection-oriented sockets such as SOCK_STREAM provide full-duplex connections and must be in a connected state before any data can be sent or received on them. A connection to another socket is created with a connect (Windows Sockets)/ WSAConnectcall. Once connected, data can be transferred using send/ WSASendand recv/ WSARecvcalls. When a session has been completed, a closesocketcall must be performed.

The communications protocols used to implement a reliable, connection-oriented socket ensure that data is not lost or duplicated. If data for which the peer protocol has buffer space cannot be successfully transmitted within a reasonable length of time, the connection is considered broken and subsequent calls will fail with the error code set to WSAETIMEDOUT.

Connectionless message-oriented sockets allow the sending and receiving of datagrams to and from arbitrary peers using sendto/ WSASendToand recvfrom/ WSARecvFrom. If such a socket is connected to a specific peer, datagrams can be sent to that peer using send/ WSASendand can be received from (only) this peer using recv/ WSARecv.

Support for the sockets with type RAWis not required, but service providers are encouraged to support raw sockets whenever possible.

Note:
The built-in service providers that the Windows Embedded CE operating system supplies do not support the WSA_FLAG_MULTIPOINT_ flags or the WSAJoinLeaf function. However, third parties can implement their own provider and have support for this function if they choose.