socket (Windows Sockets)

Article
06/30/2006

This function creates a socket that is bound to a specific service provider.

SOCKET socket(
  int af,
  int type,
  int protocol
);

Parameters

af
[in] Address family specification.

type
[in] Type specification for the new socket.

The following table shows the two type specifications supported for Winsock 1.1*.*

Type	Description
SOCK_STREAM	Provides sequenced, reliable, two-way, connection-based byte streams with an out of band (OOB) data transmission mechanism. Uses TCP for the Internet address family.
SOCK_DGRAM	Supports datagrams, which are connectionless, unreliable buffers of a fixed (typically small) maximum length. Uses UDP for the Internet address family.

In Winsock 2.2, many new socket types will be introduced and no longer need to be specified because an application can dynamically discover the attributes of each available transport protocol through the WSAEnumProtocols function. Socket type definitions appear in Winsock2.h, which will be periodically updated as new socket types, address families, and protocols are defined.

protocol
[in] Protocol to be used with the socket that is specific to the indicated address family.

Return Values

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. The following table shows a list of possible error codes.

Error code	Description
WSANOTINITIALISED	A successful WSAStartup call must occur before using this function.
WSAENETDOWN	The network subsystem or the associated service provider has failed.
WSAEAFNOSUPPORT	The specified address family is not supported.
WSAEINPROGRESS	A blocking Winsock call is in progress, or the service provider is still processing a callback function.
WSAEMFILE	No more socket descriptors are available.
WSAENOBUFS	No buffer space is available. The socket cannot be created.
WSAEPROTONOSUPPORT	The specified protocol is not supported.
WSAEPROTOTYPE	The specified protocol is the wrong type for this socket.
WSAESOCKTNOSUPPORT	The specified socket type is not supported in this address family.

Remarks

This function causes a socket descriptor and any related resources to be allocated and bound to a specific transport-service provider. Windows Sockets will use the first available service provider that supports the requested combination of address family, socket type, and protocol parameters. The socket that is created will have the overlapped attribute as a default.

Sockets with the overlapped attribute can be created by using WSASocket. All functions that allow overlapped operation (WSASend, WSARecv, WSASendTo, WSARecvFrom, and WSAIoctl) also support nonoverlapped usage on an overlapped socket if the values for parameters related to overlapped operation are NULL.

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

Important 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 protocol parameter.

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 it. A connection to another socket is created with a connect (Windows Sockets) call. Once connected, data can be transferred using send and recv calls. When a session has been completed, a closesocket call 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 and recvfrom. If such a socket is connected to a specific peer, datagrams can be sent to that peer using send and can be received only from this peer using recv.

Support for the sockets with type RAW is not required, but service providers are encouraged to support raw sockets as practicable.

Notes for IrDA Sockets

The Af_irda.h header file must be explicitly included.
Only SOCK_STREAM is supported; the SOCK_DGRAM type is not supported by IrDA.
The protocol parameter is always set to zero for IrDA.

Note On Windows NT® and Windows 2000, raw socket support requires administrative privileges.

Notes for Bluetooth Sockets

The ws2bth.h header file must be explicitly included.
Only SOCK_STREAM is supported; the SOCK_DGRAM type is not supported by Bluetooth.
The protocol parameter is always set to BTHPROTO_RFCOMM for Bluetooth.

Requirements

OS Versions: Windows CE 1.0 and later.
Header: Winsock2.h.
Link Library: Ws2.lib.

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