socket function

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

Syntax


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

Parameters

af [in]

The address family specification. Possible values for the address family are defined in the Winsock2.h header file.

On the Windows 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.

AfMeaning
AF_UNSPEC
0

The address family is unspecified.

AF_INET
2

The Internet Protocol version 4 (IPv4) address family.

AF_IPX
6

The IPX/SPX address family. This address family is only supported if the NWLink IPX/SPX NetBIOS Compatible Transport protocol is installed.

This address family is not supported on Windows Vista and later.

AF_APPLETALK
16

The AppleTalk address family. This address family is only supported if the AppleTalk protocol is installed.

This address family is not supported on Windows Vista and later.

AF_NETBIOS
17

The NetBIOS address family. This address family is only supported if the Windows Sockets provider for NetBIOS is installed.

The Windows Sockets provider for NetBIOS is supported on 32-bit versions of Windows. This provider is installed by default on 32-bit versions of Windows.

The Windows Sockets provider for NetBIOS is not supported on 64-bit versions of windows including Windows 7, Windows Server 2008, Windows Vista, Windows Server 2003, or Windows XP.

The Windows Sockets provider for NetBIOS only supports sockets where the type parameter is set to SOCK_DGRAM.

The Windows Sockets provider for NetBIOS is not directly related to the NetBIOS programming interface. The NetBIOS programming interface is not supported on Windows Vista, Windows Server 2008, and later.

AF_INET6
23

The Internet Protocol version 6 (IPv6) address family.

AF_IRDA
26

The Infrared Data Association (IrDA) address family.

This address family is only supported if the computer has an infrared port and driver installed.

AF_BTH
32

The Bluetooth address family.

This address family is supported on Windows XP with SP2 or later if the computer has a Bluetooth adapter and driver installed.

 

type [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:

TypeMeaning
SOCK_STREAM
1

A socket type that provides sequenced, reliable, two-way, connection-based byte streams with an OOB data transmission mechanism. This socket type uses the Transmission Control Protocol (TCP) for the Internet address family (AF_INET or AF_INET6).

SOCK_DGRAM
2

A socket type that supports datagrams, which are connectionless, unreliable buffers of a fixed (typically small) maximum length. This socket type uses the User Datagram Protocol (UDP) for the Internet address family (AF_INET or AF_INET6).

SOCK_RAW
3

A socket type that provides a raw socket that allows an application to manipulate the next upper-layer protocol header. To manipulate the IPv4 header, the IP_HDRINCL socket option must be set on the socket. To manipulate the IPv6 header, the IPV6_HDRINCL socket option must be set on the socket.

SOCK_RDM
4

A socket type that provides a reliable message datagram. An example of this type is the Pragmatic General Multicast (PGM) multicast protocol implementation in Windows, often referred to as reliable multicast programming.

This type value is only supported if the Reliable Multicast Protocol is installed.

SOCK_SEQPACKET
5

A socket type that provides a pseudo-stream packet based on datagrams.

 

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 [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 Windows 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.

protocolMeaning
IPPROTO_ICMP
1

The Internet Control Message Protocol (ICMP). This is a possible value when the af parameter is AF_UNSPEC, AF_INET, or AF_INET6 and the type parameter is SOCK_RAW or unspecified.

This protocol value is supported on Windows XP and later.

IPPROTO_IGMP
2

The Internet Group Management Protocol (IGMP). This is a possible value when the af parameter is AF_UNSPEC, AF_INET, or AF_INET6 and the type parameter is SOCK_RAW or unspecified.

This protocol value is supported on Windows XP and later.

BTHPROTO_RFCOMM
3

The Bluetooth Radio Frequency Communications (Bluetooth RFCOMM) protocol. This is a possible value when the af parameter is AF_BTH and the type parameter is SOCK_STREAM.

This protocol value is supported on Windows XP with SP2 or later.

IPPROTO_TCP
6

The Transmission Control Protocol (TCP). This is a possible value when the af parameter is AF_INET or AF_INET6 and the type parameter is SOCK_STREAM.

IPPROTO_UDP
17

The User Datagram Protocol (UDP). This is a possible value when the af parameter is AF_INET or AF_INET6 and the type parameter is SOCK_DGRAM.

IPPROTO_ICMPV6
58

The Internet Control Message Protocol Version 6 (ICMPv6). This is a possible value when the af parameter is AF_UNSPEC, AF_INET, or AF_INET6 and the type parameter is SOCK_RAW or unspecified.

This protocol value is supported on Windows XP and later.

IPPROTO_RM
113

The PGM protocol for reliable multicast. This is a possible value when the af parameter is AF_INET and the type parameter is SOCK_RDM. On the Windows SDK released for Windows Vista and later, this protocol is also called IPPROTO_PGM.

This protocol value is only supported if the Reliable Multicast Protocol is installed.

 

Return value

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.

Error codeMeaning
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.

Note  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

The following example demonstrates the use of the socket function to create a socket that is bound to a specific transport service provider..


#ifndef UNICODE
#define UNICODE 1
#endif

// link with Ws2_32.lib
#pragma comment(lib,"Ws2_32.lib")

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <stdlib.h>   // Needed for _wtoi


int __cdecl wmain(int argc, wchar_t **argv)
{

    //-----------------------------------------
    // Declare and initialize variables
    WSADATA wsaData = {0};
    int iResult = 0;

//    int i = 1;

    SOCKET sock = INVALID_SOCKET;
    int iFamily = AF_UNSPEC;
    int iType = 0;
    int iProtocol = 0;

    // Validate the parameters
    if (argc != 4) {
        wprintf(L"usage: %s <addressfamily> <type> <protocol>\n", argv[0]);
        wprintf(L"socket opens a socket for the specified family, type, & protocol\n");
        wprintf(L"%ws example usage\n", argv[0]);
        wprintf(L"   %ws 0 2 17\n", argv[0]);
        wprintf(L"   where AF_UNSPEC=0 SOCK_DGRAM=2 IPPROTO_UDP=17\n", argv[0]);
        return 1;
    }

    iFamily = _wtoi(argv[1]);
    iType = _wtoi(argv[2]);
    iProtocol = _wtoi(argv[3]);
    
    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        wprintf(L"WSAStartup failed: %d\n", iResult);
        return 1;
    }

    wprintf(L"Calling socket with following parameters:\n");
    wprintf(L"  Address Family = ");
    switch (iFamily) {
    case AF_UNSPEC:
        wprintf(L"Unspecified");
        break;
    case AF_INET:
        wprintf(L"AF_INET (IPv4)");
        break;
    case AF_INET6:
        wprintf(L"AF_INET6 (IPv6)");
        break;
    case AF_NETBIOS:
        wprintf(L"AF_NETBIOS (NetBIOS)");
        break;
    case AF_BTH:
        wprintf(L"AF_BTH (Bluetooth)");
        break;
    default:
        wprintf(L"Other");
        break;
    }
    wprintf(L" (%d)\n", iFamily);
    
    wprintf(L"  Socket type = ");
    switch (iType) {
    case 0:
        wprintf(L"Unspecified");
        break;
    case SOCK_STREAM:
        wprintf(L"SOCK_STREAM (stream)");
        break;
    case SOCK_DGRAM:
        wprintf(L"SOCK_DGRAM (datagram)");
        break;
    case SOCK_RAW:
        wprintf(L"SOCK_RAW (raw)");
        break;
    case SOCK_RDM:
        wprintf(L"SOCK_RDM (reliable message datagram)");
        break;
    case SOCK_SEQPACKET:
        wprintf(L"SOCK_SEQPACKET (pseudo-stream packet)");
        break;
    default:
        wprintf(L"Other");
        break;
    }
    wprintf(L" (%d)\n", iType);

    wprintf(L"  Protocol = %d = ", iProtocol);
    switch (iProtocol) {
    case 0:
        wprintf(L"Unspecified");
        break;
    case IPPROTO_ICMP:
        wprintf(L"IPPROTO_ICMP (ICMP)");
        break;
    case IPPROTO_IGMP:
        wprintf(L"IPPROTO_IGMP (IGMP)");
        break;
    case IPPROTO_TCP:
        wprintf(L"IPPROTO_TCP (TCP)");
        break;
    case IPPROTO_UDP:
        wprintf(L"IPPROTO_UDP (UDP)");
        break;
    case IPPROTO_ICMPV6:
        wprintf(L"IPPROTO_ICMPV6 (ICMP Version 6)");
        break;
    default:
        wprintf(L"Other");
        break;
    }
    wprintf(L" (%d)\n", iProtocol);

    sock = socket(iFamily, iType, iProtocol);
    if (sock == INVALID_SOCKET) 
        wprintf(L"socket function failed with error = %d\n", WSAGetLastError() );
    else {
        wprintf(L"socket function succeeded\n");

        // Close the socket to release the resources associated
        // Normally an application calls shutdown() before closesocket 
        //   to  disables sends or receives on a socket first
        // This isn't needed in this simple sample
        iResult = closesocket(sock);
        if (iResult == SOCKET_ERROR) {
            wprintf(L"closesocket failed with error = %d\n", WSAGetLastError() );
            WSACleanup();
            return 1;
        }    
    }

    WSACleanup();

    return 0;
}

Windows Phone 8: This API is supported.

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Header

Winsock2.h

Library

Ws2_32.lib

DLL

Ws2_32.dll

See also

accept
bind
closesocket
connect
getsockname
getsockopt
ioctlsocket
IPPROTO_IP Socket Options
IPPROTO_IPV6 Socket Options
listen
recv
recvfrom
Reliable Multicast Programming
select
send
sendto
setsockopt
shutdown
Winsock Functions
Winsock Reference
WSASocket