MSDN / Community / Networking / Sockets

Understanding Windows Sockets API (Winsock)

Posted by jdoe on

The Windows Sockets API (Winsock) provides a standard interface for network communication on Windows. Below is a simple example of a TCP client using Winsock2.

#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "Ws2_32.lib")

int main() {
    WSADATA wsaData;
    SOCKET ConnectSocket = INVALID_SOCKET;
    struct addrinfo *result = NULL,
                    hints;
    const char *sendbuf = "Hello Server";
    char recvbuf[512];
    int iResult, recvbuflen = 512;

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed: %d\n", iResult);
        return 1;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    // Resolve the server address and port
    iResult = getaddrinfo("example.com", "80", &hints, &result);
    if ( iResult != 0 ) {
        printf("getaddrinfo failed: %d\n", iResult);
        WSACleanup();
        return 1;
    }

    // Create a SOCKET for connecting to server
    ConnectSocket = socket(result->ai_family, result->ai_socktype,
        result->ai_protocol);
    if (ConnectSocket == INVALID_SOCKET) {
        printf("Error at socket(): %ld\\n", WSAGetLastError());
        freeaddrinfo(result);
        WSACleanup();
        return 1;
    }

    // Connect to server.
    iResult = connect( ConnectSocket, result->ai_addr, (int)result->ai_addrlen);
    if (iResult == SOCKET_ERROR) {
        closesocket(ConnectSocket);
        ConnectSocket = INVALID_SOCKET;
        printf("Unable to connect to server!\\n");
    }

    freeaddrinfo(result);

    if (ConnectSocket == INVALID_SOCKET) {
        printf("Unable to connect to server!\\n");
        WSACleanup();
        return 1;
    }

    // Send an initial buffer
    iResult = send( ConnectSocket, sendbuf, (int)strlen(sendbuf), 0 );
    if (iResult == SOCKET_ERROR) {
        printf("send failed: %d\\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    printf("Bytes Sent: %d\\n", iResult);

    // Shutdown the connection for sending since no more data will be sent
    iResult = shutdown(ConnectSocket, SD_SEND);
    if (iResult == SOCKET_ERROR) {
        printf("shutdown failed: %d\\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    // Receive data until the server closes the connection
    do {
        iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
        if ( iResult > 0 )
            printf("Bytes received: %d\\n", iResult);
        else if ( iResult == 0 )
            printf("Connection closed\\n");
        else
            printf("recv failed: %d\\n", WSAGetLastError());
    } while( iResult > 0 );

    // cleanup
    closesocket(ConnectSocket);
    WSACleanup();

    return 0;
}

Key points to remember:

Comments (0)