WSADATA structure (winsock2.h)

The WSADATA structure contains information about the Windows Sockets implementation.

Syntax

typedef struct WSAData {
  WORD           wVersion;
  WORD           wHighVersion;
#if ...
  unsigned short iMaxSockets;
#if ...
  unsigned short iMaxUdpDg;
#if ...
  char           *lpVendorInfo;
#if ...
  char           szDescription[WSADESCRIPTION_LEN + 1];
#if ...
  char           szSystemStatus[WSASYS_STATUS_LEN + 1];
#else
  char           szDescription[WSADESCRIPTION_LEN + 1];
#endif
#else
  char           szSystemStatus[WSASYS_STATUS_LEN + 1];
#endif
#else
  unsigned short iMaxSockets;
#endif
#else
  unsigned short iMaxUdpDg;
#endif
#else
  char           *lpVendorInfo;
#endif
} WSADATA, *LPWSADATA;

Members

wVersion

Type: WORD

The version of the Windows Sockets specification that the Ws2_32.dll expects the caller to use. The high-order byte specifies the minor version number; the low-order byte specifies the major version number.

wHighVersion

Type: WORD

The highest version of the Windows Sockets specification that the Ws2_32.dll can support. The high-order byte specifies the minor version number; the low-order byte specifies the major version number.

This is the same value as the wVersion member when the version requested in the wVersionRequested parameter passed to the WSAStartup function is the highest version of the Windows Sockets specification that the Ws2_32.dll can support.

iMaxSockets

Type: unsigned short

The maximum number of sockets that may be opened. This member should be ignored for Windows Sockets version 2 and later.

The iMaxSockets member is retained for compatibility with Windows Sockets specification 1.1, but should not be used when developing new applications. No single value can be appropriate for all underlying service providers. The architecture of Windows Sockets changed in version 2 to support multiple providers, and the WSADATA structure no longer applies to a single vendor's stack.

iMaxUdpDg

Type: unsigned short

The maximum datagram message size. This member is ignored for Windows Sockets version 2 and later.

The iMaxUdpDg member is retained for compatibility with Windows Sockets specification 1.1, but should not be used when developing new applications. The architecture of Windows Sockets changed in version 2 to support multiple providers, and the WSADATA structure no longer applies to a single vendor's stack. For the actual maximum message size specific to a particular Windows Sockets service provider and socket type, applications should use getsockopt to retrieve the value of option SO_MAX_MSG_SIZE after a socket has been created.

lpVendorInfo

Type: char FAR*

A pointer to vendor-specific information. This member should be ignored for Windows Sockets version 2 and later.

The lpVendorInfo member is retained for compatibility with Windows Sockets specification 1.1. The architecture of Windows Sockets changed in version 2 to support multiple providers, and the WSADATA structure no longer applies to a single vendor's stack. Applications needing to access vendor-specific configuration information should use getsockopt to retrieve the value of option PVD_CONFIG for vendor-specific information.

szDescription[WSADESCRIPTION_LEN + 1]

Type: char[WSADESCRIPTION_LEN+1]

A NULL-terminated ASCII string into which the Ws2_32.dll copies a description of the Windows Sockets implementation. The text (up to 256 characters in length) can contain any characters except control and formatting characters. The most likely use that an application would have for this member is to display it (possibly truncated) in a status message.

szSystemStatus[WSASYS_STATUS_LEN + 1]

Type: char[WSASYS_STATUS_LEN+1]

A NULL-terminated ASCII string into which the Ws2_32.dll copies relevant status or configuration information. The Ws2_32.dll should use this parameter only if the information might be useful to the user or support staff. This member should not be considered as an extension of the szDescription parameter.

Remarks

The WSAStartup function initiates the use of the Windows Sockets DLL by a process. The WSAStartup function returns a pointer to the
WSADATA structure in the lpWSAData parameter.

The current version of the Windows Sockets specification returned in the wHighVersion member of the
WSADATA structure is version 2.2 encoded with the major version number in the low-byte and the minor version number in the high-byte. This version of the current Winsock DLL, Ws2_32.dll, supports applications that request any of the following versions of the Windows Sockets specification:

• 1.0
• 1.1
• 2.0
• 2.1
• 2.2

Examples

The following example demonstrates the use of the WSADATA structure.

WORD wVersionRequested;
WSADATA wsaData;
int err;
 
wVersionRequested = MAKEWORD( 2, 2 );
 
err = WSAStartup( wVersionRequested, &wsaData );
if ( err != 0 ) {
    /* Tell the user that we could not find a usable */
    /* WinSock DLL.                                  */
    return;
}
 
/* Confirm that the WinSock DLL supports 2.2.*/
/* Note that if the DLL supports versions greater    */
/* than 2.2 in addition to 2.2, it will still return */
/* 2.2 in wVersion since that is the version we      */
/* requested.                                        */
 
if ( LOBYTE( wsaData.wVersion ) != 2 ||
        HIBYTE( wsaData.wVersion ) != 2 ) {
    /* Tell the user that we could not find a usable */
    /* WinSock DLL.                                  */
    WSACleanup( );
    return; 
}
 
/* The WinSock DLL is acceptable. Proceed. */

Requirements

See also

SOL_SOCKET Socket Options

Socket Options and IOCTLs

WSAStartup

getsockopt