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

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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.