Creating a Socket

Creating a Socket

If you're familiar with Winsock, you know that the API is based on the concept of a socket. A socket is a handle to a transport provider. In Windows, a socket is not the same thing as a file descriptor and therefore is a separate type: SOCKET in WINSOCK2.H. There are two functions that can be used to create a socket: socket and WSASocket. The next three chapters describe socket creation for each of the available protocols in great detail. For simplicity, we will briefly describe socket:

SOCKET socket (     int af,     int type,     int protocol );

The first parameter, af, is the protocol's address family. Since we describe Winsock in this chapter using only the IPv4 protocol, you should set this field to AF_INET. The second parameter, type, is the protocol's socket type. When you are creating a socket to use TCP/IP, set this field to SOCK_STREAM, for UDP/IP use SOCK_DGRAM. The third parameter is protocol and is used to qualify a specific transport if there are multiple entries for the given address family and socket type. For TCP you should set this field to IPPROTO_TCP; for UDP use IPPROTO_UDP. Chapter 2 describes socket creation in greater detail for all protocols, including the WSASocket API.

Winsock features four useful functions to control various socket options and socket behaviors: setsockopt, getsockopt, ioctlsocket, and WSAIoctl. For simple Winsock programming, you will not need to use them specifically. Chapter 7 describes each of these functions and all the available options. Once you have successfully created a socket, you are ready to set up communication on the socket to prepare it for sending and receiving data. In Winsock there are two basic communication techniques: connection-oriented and connectionless communication.