socket
The socket function creates a socket that is bound to a specific transport service provider.
Syntax
SOCKET socket(
int af,
int type,
int protocol
)
Parameters
af
Type: int
[in]
The address family specification. Possible values for the address family are defined in the Winsock2.h header file.
On the Microsoft Windows Software Development Kit (SDK) released for Windows Vista and later, the organization of header files has changed and the possible values for the address family are defined in the Ws2def.h header file. Note that the Ws2def.h header file is automatically included in Winsock2.h, and should never be used directly.
The values currently supported are AF_INET or AF_INET6, which are the Internet address family formats for IPv4 and IPv6. Other options for address family (AF_NETBIOS for use with NetBIOS, for example) are supported if a Windows Sockets service provider for the address family is installed. Note that the values for the AF_ address family and PF_ protocol family constants are identical (for example, AF_INET and PF_INET), so either constant can be used.
The table below lists common values for address family although many other values are possible.
type
Type: int
[in]
The type specification for the new socket. Possible values for the socket type are defined in the Winsock2.h header file.
The following table lists the possible values for the type parameter supported for Windows Sockets 2:
In Windows Sockets 2, new socket types were introduced. An application can dynamically discover the attributes of each available transport protocol through the WSAEnumProtocols function. So an application can determine the possible socket type and protocol options for an address family and use this information when specifying this parameter. Socket type definitions in the Winsock2.h and Ws2def.h header files will be periodically updated as new socket types, address families, and protocols are defined.
In Windows Sockets 1.1, the only possible socket types are SOCK_DGRAM and SOCK_STREAM.
protocol
Type: int
[in]
The protocol to be used. The possible options for the protocol parameter are specific to the address family and socket type specified. Possible values for the protocol are defined in the Winsock2.h and Wsrm.h header files.
On the Microsoft Windows Software Development Kit (SDK) released for Windows Vista and later, the organization of header files has changed and this parameter can be one of the values from the IPPROTO enumeration type defined in the Ws2def.h header file. Note that the Ws2def.h header file is automatically included in Winsock2.h, and should never be used directly.
If a value of 0 is specified, the caller does not wish to specify a protocol and the service provider will choose the protocol to use.
When the af parameter is AF_INET or AF_INET6 and the type is SOCK_RAW, the value specified for the protocol is set in the protocol field of the IPv6 or IPv4 packet header.
The table below lists common values for the protocol although many other values are possible.
Return value
Type: SOCKET
If no error occurs, socket returns a descriptor referencing the new socket. Otherwise, a value of INVALID_SOCKET is returned, and a specific error code can be retrieved by calling WSAGetLastError.
Return codes
| Return 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. For example, an application tried to create a socket for the AF_IRDA address family but an infrared adapter and device driver is not installed on the local computer. |
| WSAEINPROGRESS | A blocking Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function. |
| WSAEMFILE | No more socket descriptors are available. |
| WSAEINVAL | An invalid argument was supplied. This error is returned if the af parameter is set to AF_UNSPEC and the type and protocol parameter are unspecified. |
| WSAEINVALIDPROVIDER | The service provider returned a version other than 2.2. |
| WSAEINVALIDPROCTABLE | The service provider returned an invalid or incomplete procedure table to the WSPStartup. |
| 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. |
| WSAEPROVIDERFAILEDINIT | The service provider failed to initialize. This error is returned if a layered service provider (LSP) or namespace provider was improperly installed or the provider fails to operate correctly. |
| WSAESOCKTNOSUPPORT | The specified socket type is not supported in this address family. |
Remarks
The socket function causes a socket descriptor and any related resources to be allocated and bound to a specific transport-service provider. Winsock will utilize 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. For Windows, the Microsoft-specific socket option, SO_OPENTYPE, defined in Mswsock.h can affect this default. See Microsoft-specific documentation for a detailed description of SO_OPENTYPE.
Sockets without 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.
Note
The manifest constant AF_UNSPEC continues to be defined in the header file but its use is strongly discouraged, as this can cause ambiguity in interpreting the value of the protocol parameter.
Applications are encouraged to use AF_INET6 for the af parameter and create a dual-mode socket that can be used with both IPv4 and IPv6.
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 call. Once connected, data can be transferred using send and recv calls. When a session has been completed, a closesocket 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 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.
IPv6 and IPv4 operate differently when receiving a socket with a type of SOCK_RAW. The IPv4 receive packet includes the packet payload, the next upper-level header (for example, the IP header for a TCP or UDP packet), and the IPv4 packet header. The IPv6 receive packet includes the packet payload and the next upper-level header. The IPv6 receive packet never includes the IPv6 packet header.
On Windows NT, raw socket support requires administrative privileges.
A socket with a type parameter of SOCK_SEQPACKET is based on datagrams, but functions as a pseudo-stream protocol. For both send and receive packets, separate datagrams are used. However, Windows Sockets can coalesce multiple receive packets into a single packet. So an application can issue a receive call (for example, recv or WSARecvEx) and retrieve the data from several coalesced multiple packets in single call. The AF_NETBIOS address family supports a type parameter of SOCK_SEQPACKET.
When the af parameter is AF_NETBIOS for NetBIOS over TCP/IP, the type parameter can be SOCK_DGRAM or SOCK_SEQPACKET. For the AF_NETBIOS address family, the protocol parameter is the LAN adapter number represented as a negative number.
On Windows XP and later, the following command can be used to list the Windows Sockets catalog to determine the service providers installed and the address family, socket type, and protocols that are supported.
netsh winsock show catalog
Support for sockets with type SOCK_RAW is not required, but service providers are encouraged to support raw sockets as practicable.
Notes for IrDA Sockets
Keep the following in mind:
- 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 0 for IrDA.
A socket for use with the AF_IRDA address family can only be created if the local computer has an infrared port and driver installed. Otherwise, a call to the socket function with af parameter set to AF_IRDA will fail and WSAGetLastError returns WSAEPROTONOSUPPORT.
Example Code
Example
The following example demonstrates the use of the socket function to create a socket that is bound to a specific transport service provider..
Windows Phone 8: This API is supported.
Requirements
Header: Declared in winsock2.h.
Library: Use ws2_32.lib.