DHCP Client API Examples

The following examples illustrate two uses of the DHCP Client API:

• Example 1 illustrates how to use the DhcpRequestParams function to retrieve a host name.
• Example 2 shows how the DhcpRegisterParamChange function can be used to keep track of host name changes.

Example 1: Using the DhcpRequestParams function

The following example illustrates how to retrieve the host name using the DhcpRequestParams function call. The name of the adapter can be retrieved using the GetInterfaceInfo structure, which is part of the Internet Protocol Helper API:

#include <windows.h>
#include <dhcpcsdk.h>

#pragma comment( lib, "dhcpcsvc.lib" )

BOOL RetrieveHostName(
    IN LPWSTR     pszAdapterName,
    IN OUT CHAR   pszHostNameBuf[], // must be large enough buffer
    IN DWORD      dwHostNameBufSize
)
/*++

Routine returns TRUE on success and FALSE on failure.

--*/
{
    DWORD dwError, dwSize;
    CHAR TmpBuffer[1000]; // host name won't be larger than this
    DHCPCAPI_PARAMS DhcpApiHostNameParams = {
            0,                // Flags
            OPTION_HOST_NAME, // OptionId
            FALSE,            // vendor specific?
            NULL,             // data filled in on return
            0                 // nBytes
        }; 
    DHCPCAPI_PARAMS_ARRAY RequestParams = {
            1,  // only one option to request 
            &amp;DhcpApiHostNameParams
        };

    DHCPCAPI_PARAMS_ARRAY SendParams = {
            0,   
            NULL
        };

    dwSize = sizeof(TmpBuffer);
    dwError = DhcpRequestParams(
            DHCPCAPI_REQUEST_SYNCHRONOUS, // Flags
            NULL,                         // Reserved
            pszAdapterName,               // Adapter Name
            NULL,                         // not using class id
               SendParams,                         // sent parameters
            RequestParams,                // requesting params
            (PBYTE) TmpBuffer,            // buffer
            &amp;dwSize,                      // buffer size
            NULL                          // Request ID
        );

    if( ERROR_MORE_DATA == dwError ) 
    {
            //
            // dwSize is not large enough.
            //
    }

    if( NO_ERROR == dwError ) 
    {

            // Check if the requested option was obtained.

            if( DhcpApiHostNameParams.nBytesData ) 
            {

                // Check size with dwHostNameBufSize.

                CopyMemory(
                     pszHostNameBuf, DhcpApiHostNameParams.Data,
                     DhcpApiHostNameParams.nBytesData
                     );
                pszHostNameBuf[DhcpApiHostNameParams.nBytesData] = '\0';
                return TRUE;
            }
    }

    return FALSE;
}

Example 2: Using the DhcpRegisterParamChange function

The following code illustrates how the DhcpRegisterParamChange function can be used to keep track of host name changes:

ULONG UpdateHostNameLoop(
    IN LPWSTR     pszAdapterName,
    IN CHAR       pszHostNameBuf[],
    IN ULONG      dwHostBufSize
)
{
    DWORD dwError;
    HANDLE hEvent;
    DHCPCAPI_PARAMS DhcpApiHostNameParams = {
            0,                 // Flags
            OPTION_HOST_NAME,  // OptionId
            FALSE,             // vendor specific?
            NULL,              // data filled in on return
            0                  // nBytes
        };
    DHCPCAPI_PARAMS_ARRAY DhcpApiParamsArray = {
        1,         // only one option to request 
        &DhcpApiHostNameParams
        };

    dwError = DhcpRegisterParamChange(
        DHCPCAPI_REGISTER_HANDLE_EVENT, // Flags
        NULL,                           // Reserved
        pszAdapterName,                 // adapter name
        NULL,                           // no class ID
        DhcpApiParamsArray,             // params of interest
        (LPVOID)&hEvent                 // event handle
        );

    if( ERROR_SUCCESS != dwError ) return dwError;

    // Wait on event all the time.

    while( WAIT_OBJECT_0 == WaitForSingleObject(hEvent, INFINITE) ) 
    {

        // Get host name and update it.

        ResetEvent(hEvent);
        dwError = RetrieveHostName(pszAdapterName, pszHostNameBuf, dwHostBufSize );
    
        // Ignore this error.

        break;
    }


    // Wait failed or retrieve failed? De-register the event handle.

    (void)DhcpDeRegisterParamChange(
        DHCPCAPI_REGISTER_HANDLE_EVENT, // Flags
        NULL,                           // Reserved
        (LPVOID) hEvent                 // event
        );

    return dwError;
}

Note

The event handle obtained by this routine must not be closed with the CloseHandle function. It should be released using the DhcpDeRegisterParamChange function in order to avoid resource leaks; the DhcpDeRegisterParamChange function releases internal resources allocated for this notification.