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Is there a way in VFP to pass a DWORD to an API function from VFP?

A customer asked:

Is there a way in VFP to pass a DWORD to an API function from VFP?

The Beep API function used in Create your own typing tutor! uses DWORDs and is called via the DECLARE - DLL Command . A DWORD is just a 32 bit value. An integer in VFP is a 32 bit value (4 bytes).

 

DECLARE integer Beep IN WIN32API integer Freq, integer DurationMs

Beep(400,1000)

Other examples of 32 bit values in the Win API abound. A LPDWORD is a Long Pointer to a DWORD, which is a 32 bit value as well (on a 32 bit machine).

See the Windows Data Types MSDN topic for more details.

The Data Type Ranges topic shows the sizes of the various types. For example, an HWND is a HANDLE which is a PVOID which is a void * which means a pointer to anything. A pointer is 32 bits (on a 32 bit machine).

The SetWindowText Function is declared:

 BOOL SetWindowText(      

    HWND hWnd,

     LPCTSTR lpString

 );

and thus is called:

DECLARE integer SetWindowText IN WIN32API integer,string

SetWindowText(_vfp.hWnd,"Test")

A VFP string is just a sequence of bytes. If a Windows API requires a structure to be passed, just pass a string of the right size. For example, see Inspect your memory image and see fragmentation for a call to VirtualQueryEx which returns a MEMORY_BASIC_INFORMATION structure. That structure is simply a sequence of bytes, so the DECLARE command looks like:

DECLARE integer VirtualQueryEx IN WIN32API integer hProcess, integer lpAddress,string @, integer dwLength

To decode/encode the string the CTOBIN( ) Function and the BINTOC( ) Function are very useful.

Comments

  • Anonymous
    January 24, 2006
    How about passing a DWORD to an OCX control? Can this be done?

    Steve
  • Anonymous
    January 24, 2006
    A DWORD is just a 32 bit value, so you can just use INTEGER for an ActiveX control
  • Anonymous
    January 24, 2006
    Would the steps below be correct?

    1. Convert the numeric FoxPro variable to be passed to a 4-byte string.



    PARAMETERS nVal

    * +----------------------------------------------------------------------------+

    * BEGIN METHOD: FOXNUMTODWORD

    * DESCRIPTION: Converts a VFP numeric value to a string that can be passed

    * to Windows API functions as a DWORD (adapted from

    * www.news2news.com.

    * REVISION: 1.0 January 23, 2006

    * DEVELOPER: Anatoliy Mogylevets borrowed by Doug Kimzey



     +----------------------------------------------------------------------------+

    #DEFINE m0 256

    #DEFINE m1 65536

    #DEFINE m2 16777216



    LOCAL b0, b1, b2, b3



    b3 = Int(nVal/m2)

    b2 = Int((nVal - b3 * m2)/m1)

    b1 = Int((nVal - b3m2 - b2m1)/m0)

    b0 = Mod(nVal, m0)



    RETURN Chr(b0)+Chr(b1)+Chr(b2)+Chr(b3)

    * +----------------------------------------------------------------------------+

    * END METHOD: FOXNUMTODWORD

    * +----------------------------------------------------------------------------+





    2. Call the OCX method with CTOBIN( FOXNUMTODWORD(nValue))

  • Anonymous
    January 24, 2006
    Doug: I don't see why you're converting a number from a VFP integer to a string and then using CTOBIN to convert back to an integer. Why not just pass the integer?
  • Anonymous
    January 25, 2006
    Calvin,

    The problem seems to occur when a numeric value is passed from a cursor. If I called OCX method:

    void CeNetOCXCtrl::DisconnectPeer(DWORD Address, LONG Port)

    from VFP using values from a cursor:

    THISFORM.eNet.DisconnectPeer( eNetCursor->nAddress, eNetCursor->nHost )

    ;where nAddress(N,12,0) = 2147942666 and nHost(I) = 48620; produces an error: Incorrect number of parameters.

    A call like this:

    THISFORM.eNet.DisconnectPeer( 2147942666, eNetCursor->nHost )

    works without a problem.

    I am not sure why this is occurring but, to be honest, I am suspicious of the OCX. I will dig in further and keep you in the loop as what the cause is.

    -Doug









  • Anonymous
    January 25, 2006
    Doug: it looks like nAddress is a real number N(12,0) and not an integer. The OCX expects an integer. Try something like INT(eNetCursor->nAddress)
  • Anonymous
    January 25, 2006
    Calvin,

    I'm sure your right. Thank you most kindly. I'll give that a shot.

    -Doug
  • Anonymous
    January 25, 2006
    Functions CTOBIN( ) and BINTOC( ) is useful to convert INT (32-bit signed integer, range -2147483648..+2147483647 ) or SHORT (16-bit signed, range -32768..+32767).

    But there is NO way how convert by these functions DWORD (32-bit unsigned integer, range 0..4294967295) or WORD (16-bit unsigned integer, range 0..65535).

    I need it very much, why isn't any more parameter for these functions to make it possible?

    Sorry for my English

    Franta

  • Anonymous
    April 24, 2006
    I was writing a sample about DECLARE DLL to show some of its features which I implemented about 12 years...
  • Anonymous
    May 01, 2006
    The comment has been removed