[Gambas-user] Migrate VB6 project to Gambas 2.0 ?

[Ron Onstenk]

On Thursday 21 February 2008 00:28, 2020 wrote:
> ' Gambas class file
> PRIVATE EXTERN FT_Open(intDeviceNumber AS Integer, plngHandle AS Pointer) AS Integer IN "libftd2xx"
> PRIVATE EXTERN FT_Close(plngHandle AS Pointer) AS Integer IN "libftd2xx"
> PRIVATE plngHandle AS Pointer = Alloc(4)
> PRIVATE intDeviceNumber AS Integer
> 


Just downloaded the source code for libftd2xx.

Module Name:  ftd2xx.h

typedef DWORD		 	*FT_HANDLE;

FTD2XX_API
FT_STATUS WINAPI FT_Open(
	int deviceNumber,
	FT_HANDLE *pHandle
	);

FTD2XX_API
FT_STATUS WINAPI FT_Close(
    FT_HANDLE ftHandle
    );

FTD2XX_API
FT_STATUS WINAPI FT_Read(
    FT_HANDLE ftHandle,
    LPVOID lpBuffer,
    DWORD nBufferSize,
    LPDWORD lpBytesReturned
    );

FTD2XX_API 
FT_STATUS WINAPI FT_Write(
    FT_HANDLE ftHandle,
    LPVOID lpBuffer,
    DWORD nBufferSize,
    LPDWORD lpBytesWritten
    );

> Q1: What do you mean by "prototype of the function in C" in your first statement.
The above snippit.


The interesting point is in the FT_Open() *pHandle is used and for all other actions ftHandle.

Both are type of *FT_HANDLE (a pointer) but in the Open() a pointer to the pointer variable pHandle
and the other are the actual pointer set by the FT_Open().

I asume in *pHandle the FT_Open will store the pointer value to the handle.

I'm not a C veteran but maybe Benoit can explain the exact difference here.
Open():	 FT_HANDLE *pHandle (give a pointer to a pointer variable to use)
Close(): FT_HANDLE ftHandle (give the pointer set by the open function)

I'm also afraid you need the VarPtr function not available in gambas<3

PRIVATE EXTERN FT_Open(intDeviceNumber AS Integer, plngHandle AS Pointer) AS Integer IN "libftd2xx"
PRIVATE EXTERN FT_Close(plngHandle AS Pointer) AS Integer IN "libftd2xx"
PRIVATE plngHandle AS Pointer = Alloc(4)

PUBLIC SUB Form_Open()
  DIM returnCodes1 AS Integer
  DIM returnCodes2 AS Integer  
' open the device
  returnCodes1 = FT_Open(0, VarPtr(plngHandle) ) '<--- the difference?
  PRINT returnCodes1, plngHandle
' close the device  
  returnCodes2 = FT_Close(plngHandle)
  PRINT returnCodes2, plngHandle
END

Ron