Re: how to get the pointer variable address from a dll

On Mon, 18 Jun 2007 08:13:27 -0700, "karunyalakshmi@gmail.com"
<karunyalakshmi@gmail.com> wrote:


....


As others have said, the problem is that you may need a new level of
indirection (pointer to a pointer).

AliR or Joe seems to have suggested using reference (&), but if your
DLL has a C-interface, I would suggest using a real
pointer-to-pointer, i.e. void ** (or LPVOID *), as COM does e.g. for
QueryInterface:

 __declspec(dllexport) BOOL TRSTMonGetStatus(LPVOID * ppBuffer);

In your function implementation:

  // Check valid parameters
  if ( ppBuffer == NULL )
    return FALSE; // Error: bad parameter

  // Clear output parameter (*ppBuffer is LPVOID)
  *ppBuffer = NULL;

  // Allocate/process what you need here...
  // Use *ppBuffer, e.g.:

  BYTE * pBytes = new BYTE[1000];
  // ...or whatever...

  // This value is returned to caller
  *ppBuffer = (LPVOID)pBytes;

Note that you should also provide in your DLL a function to *release*
the buffer:

__declspec(dllexport) void TRSTMonReleaseBuffer(LPVOID * ppBuffer)
{
  if ( ppBuffer == NULL )
    return;

  BYTE * pBytes = (BYTE*) (*ppBuffer);
  if ( pBytes == NULL )
    return;

  // Release the allocated array
  delete [] pBytes;

  // Clear caller pointer
  *ppBuffer = NULL;
}

You can use your code like so:

  // The caller
  LPVOID pBuffer = NULL;
  if ( TRSTMonGetStatus( &pBuffer ) ... )

  // ... Work ...

  // Release
  TRSTMonReleaseBuffer( &pBuffer );

(BTW: I've not tested the code with the compiler...)

MrAsm