Core Concepts

WinSock enables applications to communicate over a network using the TCP/IP protocol suite. It abstracts the underlying network hardware and protocols, providing a consistent interface for developers.

• Sockets: Endpoints for communication.
• Protocols: TCP (reliable, connection-oriented) and UDP (unreliable, connectionless).
• Address Families: AF_INET for IPv4, AF_INET6 for IPv6.
• I/O Control (IOCTL): For managing socket behavior.

Key Functions

Socket Creation and Initialization

• socket(): Creates a socket.
• WSASocket(): Creates a socket with extended options.
• WSAStartup(): Initializes the Winsock library.
• WSACleanup(): Cleans up the Winsock library.

Address Information

• bind(): Assigns a local protocol address to a socket.
• connect(): Establishes a connection to a remote socket.
• listen(): Puts a socket into a listening state.
• accept(): Accepts a connection on a socket.
• gethostbyname(), getaddrinfo(): Resolve hostnames to IP addresses.

Data Transfer

• send(), WSASend(): Sends data on a socket.
• recv(), WSARecv(): Receives data from a socket.
• sendto(), WSASendTo(): Sends data to a specific address.
• recvfrom(), WSARecvFrom(): Receives data from a specific address.

Socket Options and Control

• setsockopt(): Sets socket options.
• getsockopt(): Gets socket options.
• ioctlsocket(): Performs I/O control operations on a socket.

Error Handling

• WSAGetLastError(): Retrieves the error code for the last Winsock function failure.

Common Structures

The following structures are frequently used with WinSock functions:

• SOCKADDR / SOCKADDR_IN / SOCKADDR_IN6: Address structure.
• WSADATA: Used by WSAStartup() to return information about the Winsock implementation.
• FD_SET: Used for socket I/O multiplexing with select().

Example: Simple TCP Client

This is a simplified example demonstrating a basic TCP client.

#include <winsock2.h>
#include <ws2tcpip.h>
#include <iostream>

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

int main() {
    WSADATA wsaData;
    SOCKET ConnectSocket = INVALID_SOCKET;
    struct sockaddr_in clientService;
    int nRet;

    // Initialize Winsock
    nRet = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (nRet != 0) {
        std::cerr << "WSAStartup failed: " << nRet << std::endl;
        return 1;
    }

    // Create a socket
    ConnectSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (ConnectSocket == INVALID_SOCKET) {
        std::cerr << "socket failed: " << WSAGetLastError() << std::endl;
        WSACleanup();
        return 1;
    }

    // Set up the connection
    clientService.sin_family = AF_INET;
    clientService.sin_addr.s_addr = inet_addr("127.0.0.1"); // Connect to localhost
    clientService.sin_port = htons(27015); // Connect to port 27015

    // Establish the connection
    nRet = connect(ConnectSocket, (SOCKADDR*)&clientService, sizeof(clientService));
    if (nRet == SOCKET_ERROR) {
        std::cerr << "connect failed: " << WSAGetLastError() << std::endl;
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    std::cout << "Connected successfully!" << std::endl;

    // ... send and receive data here ...

    // Cleanup
    closesocket(ConnectSocket);
    WSACleanup();

    return 0;
}

Further Reading

• Network Addressing
• Network Connections
• Internet Protocols