The Windows Sockets WSAStartup function initiates use of WS2_32.DLL by a process.
int WSAStartup (
WORD wVersionRequested,
LPWSADATA lpWSAData
);
The WSAStartup 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 to retrieve details of the specific Windows Sockets implementation. The application or DLL can only issue further Windows Sockets functions after a successfully calling WSAStartup.
In order to support future Windows Sockets implementations and applications that can have functionality differences from current version of Windows Sockets, a negotiation takes place in WSAStartup. The caller of WSAStartup and the WS2_32.DLL indicate to each other the highest version that they can support, and each confirms that the other's highest version is acceptable. Upon entry to WSAStartup, the WS2_32.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. The WS2_32.DLL then assumes that the application will use wVersion. If the wVersion field of the WSADATA structure is unacceptable to the caller, it should call WSACleanup and either search for another WS2_32.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 than the version of this specification. In such a 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, for example, may be inaccessible. To be guaranteed full access to 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 a WS2_32.DLL and a Windows Sockets application to support a range of Windows Sockets versions. An application can use WS2_32.DLL if there is any overlap in the version ranges. The following chart gives examples of how WSAStartup works in conjunction with different application and WS2_32.DLL versions:
| App versions | DLL Versions | wVersion Requested |
wVersion | wHigh Version |
End 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 2.0 | 1.1 | 2.0 | 1.1 | 1.1 | use 1.1 |
| 2.0 | 2.0 | 2.0 | 2.0 | 2.0 | use 2.0 |
The following code fragment demonstrates how an application that supports only version 2.2 of Windows Sockets 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 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. */
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 the WS2_32.DLL, the application or DLL must call WSACleanup in order to allow the WS2_32.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 call one WSACleanup call for every successful WSAStartup call to allow third-party DLLs to make use of a WS2_32.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 deallocation for the task.
The WSAStartup function returns zero if successful. Otherwise, it returns one of the error codes listed below.
An application cannot call WSAGetLastError to determine the error code as is normally done in Windows Sockets is WSAStartup fails. The WS2_32.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.
| 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. |
| WSAEINPROGRESS | A blocking Windows Sockets 1.1 operation is in progress. |
| WSAEPROCLIM | Limit on the number of tasks supported by the Windows Sockets implementation has been reached. |
| WSAEFAULT | The lpWSAData is not a valid pointer. |
Windows NT: Yes
Windows: Yes
Windows CE: Use version 1.0 and later.
Header: Declared in winsock2.h.
Import Library: Link with ws2_32.lib.