WSAStartup

Article
06/30/2006

This function initiates use of ws2.dll by a process.

int WSAStartup(
  WORD wVersionRequested,
  LPWSADATA lpWSAData
);

Parameters

wVersionRequested
[in] Highest version of Windows Sockets support that the caller can use. The high-order byte specifies the minor version (revision) number; the low-order byte specifies the major version number.
lpWSAData
[out] Pointer to the WSADATA structure that is to receive details of the Windows Sockets implementation.

Return Values

If no error occurs, this function returns zero. If an error occurs, it returns one of the error codes listed in the following table.

An application cannot call WSAGetLastError to determine the error code as is typcally done in Windows Sockets if WSAStartup fails. ws2.dll will not have been loaded in the case of a failure so the client data area where the last error information is stored could not be established.

The following table shows a list of possible error codes.

Error code	Description
WSASYSNOTREADY	Indicates that the underlying network subsystem is not ready for network communication.
WSAVERNOTSUPPORTED	The version of Windows Sockets support requested is not provided by this particular Windows Sockets implementation.
WSAEPROCLIM	A limit on the number of tasks supported by the Windows Sockets implementation has been reached.
WSAEFAULT	The lpWSAData parameter is not a valid pointer.

Remarks

This function must be the first Windows Sockets function called by an application or DLL. It allows an application or DLL to specify the version of Windows Sockets required and retrieve details of the specific Windows Sockets implementation. The application or DLL can only issue further Windows Sockets functions after successfully calling WSAStartup.

To support future Windows Sockets implementations and applications that can have functionality differences from the current version of Windows Sockets, a negotiation takes place in WSAStartup. The caller of WSAStartup and ws2.dll indicate to each other the highest version that they can support, and each confirms that the other's highest version is acceptable. On entry to WSAStartup, ws2.dll examines the version requested by the application. If this version is equal to or higher than the lowest version supported by the DLL, the call succeeds and the DLL returns in wHighVersion the highest version it supports and in wVersion the minimum of its high version and wVersionRequested. ws2.dll then assumes that the application will use wVersion. If the wVersion parameter of the WSADATA structure is unacceptable to the caller, it should call WSACleanup and either search for another ws2.dll or fail to initialize.

It is legal and possible for an application written to this version of the specification to successfully negotiate a higher version number version. In that case, the application is only guaranteed access to higher version functionality that fits within the syntax defined in this version, such as new Ioctl codes and new behavior of existing functions. New functions may be inaccessible. To get full access to the new syntax of a future version, the application must fully conform to that future version, such as compiling against a new header file, linking to a new library, or other special cases.

This negotiation allows both ws2.dll and a Windows Sockets application to support a range of Windows Sockets versions. An application can use ws2.dll if there is any overlap in the version ranges. The following table shows how WSAStartup works with different applications and ws2.dll versions.

Application version	DLL version	wVersion requested	wVersion	wHigh version	Result
1.1	1.1	1.1	1.1	1.1	use 1.1
1.0 1.1	1.0	1.1	1.0	1.0	use 1.0
1.0	1.0 1.1	1.0	1.0	1.1	use 1.0
1.1	1.0 1.1	1.1	1.1	1.1	use 1.1
1.1	1.0	1.1	1.0	1.0	Application fails
1.0	1.1	1.0	---	---	WSAVERNOT SUPPORTED
1.0 1.1	1.0 1.1	1.1	1.1	1.1	use 1.1
1.1 2.2	1.1	2.2	1.1	1.1	use 1.1
2.2	2.2	2.2	2.2	2.2	use 2.2

Example

The following code sample demonstrates how an application that supports only Winsock 2.2 makes a WSAStartup call.

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 later    */
/* 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. */

Once an application or DLL has made a successful WSAStartup call, it can proceed to make other Windows Sockets calls as needed. When it has finished using the services of ws2.dll, the application or DLL must call WSACleanup to allow ws2.dll to free any resources for the application.

Details of the actual Windows Sockets implementation are described in the WSADATA structure.

An application or DLL can call WSAStartup more than once if it needs to obtain the WSADATA structure information more than once. On each such call the application can specify any version number supported by the DLL.

An application must make one WSACleanup call for every successful WSAStartup call to allow third-party DLLs to make use of ws2.dll on behalf of an application. This means, for example, that if an application calls WSAStartup three times, it must call WSACleanup three times. The first two calls to WSACleanup do nothing except decrement an internal counter; the final WSACleanup call for the task does all necessary resource de-allocation for the task.

Requirements

OS Versions: Windows CE 1.0 and later.
Header: Winsock2.h.
Link Library: Ws2.lib.

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