Winsock API: connect

参考MSDN:http://msdn.microsoft.com/en-us/library/windows/desktop/ms737625(v=vs.85).aspx

The connect function establishes a connection to a specified socket.

Syntax

int connect(
  _In_  SOCKET s,
  _In_  const struct sockaddr *name,
  _In_  int namelen
);

Parameters

s [in]

A descriptor identifying an unconnected socket.

name [in]

A pointer to the sockaddr structure to which the connection should be established.

namelen [in]

The length, in bytes, of the sockaddr structure pointed to by the name parameter.

Return value

If no error occurs, connect returns zero. Otherwise, it returns SOCKET_ERROR, and a specific error code can be retrieved by callingWSAGetLastError.

On a blocking socket, the return value indicates success or failure of the connection attempt.

With a nonblocking socket, the connection attempt cannot be completed immediately. In this case,connect will return SOCKET_ERROR, and WSAGetLastError will return WSAEWOULDBLOCK. In this case, there are three possible scenarios:

• Use the select function to determine the completion of the connection request by checking to see if the socket is writeable.
• If the application is using WSAAsyncSelect to indicate interest in connection events, then the application will receive an FD_CONNECT notification indicating that theconnect operation is complete (successfully or not).
• If the application is using WSAEventSelect to indicate interest in connection events, then the associated event object will be signaled indicating that theconnect operation is complete (successfully or not).

Example Code

The following example demonstrates the use of the connect function.

#ifndef UNICODE#define UNICODE#endif#define WIN32_LEAN_AND_MEAN#include <winsock2.h>#include <ws2tcpip.h>#include <stdio.h>// Need to link with Ws2_32.lib#pragma comment(lib, "ws2_32.lib")int wmain(){    //----------------------    // Initialize Winsock    WSADATA wsaData;    int iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);    if (iResult != NO_ERROR) {        wprintf(L"WSAStartup function failed with error: %d\n", iResult);        return 1;    }    //----------------------    // Create a SOCKET for connecting to server    SOCKET ConnectSocket;    ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);    if (ConnectSocket == INVALID_SOCKET) {        wprintf(L"socket function failed with error: %ld\n", WSAGetLastError());        WSACleanup();        return 1;    }    //----------------------    // The sockaddr_in structure specifies the address family,    // IP address, and port of the server to be connected to.    sockaddr_in clientService;    clientService.sin_family = AF_INET;    clientService.sin_addr.s_addr = inet_addr("127.0.0.1");    clientService.sin_port = htons(27015);    //----------------------    // Connect to server.    iResult = connect(ConnectSocket, (SOCKADDR *) & clientService, sizeof (clientService));    if (iResult == SOCKET_ERROR) {        wprintf(L"connect function failed with error: %ld\n", WSAGetLastError());        iResult = closesocket(ConnectSocket);        if (iResult == SOCKET_ERROR)            wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());        WSACleanup();        return 1;    }    wprintf(L"Connected to server.\n");    iResult = closesocket(ConnectSocket);    if (iResult == SOCKET_ERROR) {        wprintf(L"closesocket function failed with error: %ld\n", WSAGetLastError());        WSACleanup();        return 1;    }    WSACleanup();    return 0;}