Windows API Reference – Network I/O

Overview

The Network I/O API for Windows provides a comprehensive set of functions for creating, configuring, and managing network communications. It includes support for sockets, address resolution, asynchronous operations, and both TCP and UDP protocols.

Key Concepts

Socket – Endpoint for sending and receiving data.
Winsock – Windows Sockets implementation, providing the underlying transport.
Asynchronous I/O – Overlapped I/O for non‑blocking operations.

Core Functions

Name	Header	Description
socket	winsock2.h	Creates a new socket.
bind	winsock2.h	Binds a socket to a local address.
connect	winsock2.h	Establishes a connection to a remote socket.
send	winsock2.h	Sends data on a connected socket.
recv	winsock2.h	Receives data from a connected socket.
getaddrinfo	ws2tcpip.h	Resolves hostnames to address structures.
freeaddrinfo	ws2tcpip.h	Frees address info returned by getaddrinfo.
WSAAsyncSelect	winsock2.h	Requests asynchronous event notification.

Simple TCP Client Example

#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "Ws2_32.lib")
int main() {
    WSADATA wsa;
    WSAStartup(MAKEWORD(2,2), &wsa);
    SOCKET s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    struct addrinfo *result = NULL, hints = {0};
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    getaddrinfo("example.com","80",&hints,&result);
    connect(s, result->ai_addr, (int)result->ai_addrlen);
    const char *msg = "GET / HTTP/1.1\r\nHost: example.com\r\n\r\n";
    send(s, msg, (int)strlen(msg), 0);
    char buf[512];
    int bytes = recv(s, buf, sizeof(buf)-1, 0);
    buf[bytes]=0;
    printf("%s",buf);
    closesocket(s);
    WSACleanup();
    return 0;
}