scoket

用于在两个基于TCP/IP协议的应用程序之间相互通信。最早出现在UNIX系统中，是UNIX系统主要的信息传递方式。在WINDOWS系统中，SOCKET称为WINSOCK。两个基本概念：客户方和服务方。当两个应用之间需要采用SOCKET通信时，首先需要在两个应用之间（可能位于同一台机器，也可能位于不同的机器）建立SOCKET连接，发起呼叫连接请求的一方为客户方，接受呼叫连接请求的一方成为服务方。客户方和服务方是相对的，同一个应用可以是客户方，也可以是服务方。在客户方呼叫连接请求之前，它必须知道服务方在哪里。所以需要知道服务方所在机器的IP地址或机器名称，如果客户方和服务方事前有一个约定就好了，这个约定就是PORT（端口号）。也就是说，客户方可以通过服务方所在机器的IP地址或机器名称和端口号唯一的确定方式来呼叫服务方。在客户方呼叫之前，服务方必须处于侦听状态，侦听是否有客户要求建立连接。一旦接到连接请求，服务方可以根据情况建立或拒绝连接。连接方式有两种，同步方式（Blocking）和(noBlocking).客户方发送的消息可以是文本，也可以是二进制信息流。当客户方的消息到达服务方端口时，会自动触发一个事件（event），服务方只要接管该事件，就可以接受来自客户方的消息了。

函数

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

SOCKET socket(

int af,

int type,

int protocol

);

Parameters

afAddress family specification.

type

Type specification for the new socket.

The following are the only two type specifications supported for WindowsSockets 1.1: Type Explanation

SOCK_STREAM Provides sequenced, reliable, two-way, connection-based byte streams with an OOB data transmission mechanism. Uses TCPfor the Internet address family.

SOCK_DGRAM Supports datagrams, which are connectionless, unreliable buffers of a fixed(typically small) maximum length. Uses UDPfor the Internet address family.

In Windows Sockets 2, many new socket types will be introduced and no longer need to bespecified, since 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

Protocol to be used with the socket that is specific to the indicated address family.

Return Values

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 code Meaning

WSANOTINITIALISED A successful WSAStartupcall 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 Windows Sockets 1.1 call is in progress, or the service provider is still processing a callback function.

WSAEMFILE No moresocket 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

The socket function causes a socket descriptor and any related resources to be allocated and bound to a specific transport-service provider. Windows Sockets 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 Microsoft operating systems, 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.

Whenselecting a protocol and its supporting service provider this procedurewill 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, as 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 connectedstate before any data can be sent or received on it. A connection to another socket is created with a connect call. Onceconnected, 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 implementa 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 peersusing 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 sockets with type SOCK_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.

OnlySOCK_STREAM is supported; the SOCK_DGRAM type is not supported by IrDA.

The protocol parameter is always set to 0 for IrDA.

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

Requirements

Windows NT/2000/XP: Included in Windows NT 3.1 and later.

Windows 95/98/Me: Included in Windows 95 and later.

Header: Declared in Winsock2.h.

Library: Use Ws2_32.lib.

See Also

Windows Sockets Programming Considerations Overview, Socket Functions, accept, bind, connect, getsockname, getsockopt, ioctlsocket, listen, recv, recvfrom, select, send, sendto, setsockopt, shutdown, WSASocket