Chapter 9 -- Socket Options and Ioctls

Chapter 9

Once a socket has been created, various attributes can be manipulated via socket options and ioctl commands to affect the behavior of the socket. Some of these options simply return information, while others affect the behavior of the socket in your application. An ioctl is an I/O control command that also affects the behavior of the socket. This chapter is dedicated to discussing four Winsock functions: getsockopt, setsockopt, ioctlsocket, and WSAIoctl. Each function has numerous commands, many of which have never been properly documented. In the following sections, we will discuss the required parameters and available options for each function as well as the platforms that support those options. Every option is assumed to work on all Win32 platforms (Windows CE, Windows 95, Windows 98, Windows NT, and Windows 2000) unless otherwise noted. The only exception occurs when an option requires Winsock 2. Because Winsock 2 is not available on every platform, Winsock 2 ioctl commands and options are not supported on Windows CE or Windows 95 (unless the Winsock 2 update has been applied to Windows 95). Furthermore, recall that Windows CE does not support any protocol-specific options not pertaining to TCP/IP.

Most of these ioctl commands and options are defined in either Winsock.h or Winsock2.h, depending on whether they are specific to Winsock 1 or Winsock 2; however, a few of the options are specific either to the Microsoft provider or to a particular transport protocol. Microsoft-specific extensions are defined in both Winsock.h and Mswsock.h. Transport provider extensions are defined in their protocol-specific header files. For the transport-specific options, we will indicate the correct header file along with the option. Applications using the Microsoft-specific extensions must link with Mswsock.lib.