Unmanaged to managed code

Unmanaged to managed code

• bitskull

  Sorry James,

  It doesn't compile Cannot marshal 'parameter #1': Cannot use SizeParamIndex for ByRef array parameters.

  :S

  Barbara

  
  

• johnof

  Hello All.

  Barbara:

  Try this:

  [DllImport("dllfilename")]   public static extern Int32 XPTO(byte aux);

  HTH.

  
  
  

• morpheus3230

  BYTE **aux returns a byte value, whereas BYTE aux** is a pointer to a pointer that points to a byte array.

  um..No. "BYTE **aux" is a pointer to a pointer to a byte. The stars attach to the BYTE, not to the aux. Hence aux is a pointer.

  Later, when I use the value aux, then the stars attach to aux:

  BYTE** ppByte = aux;

  BYTE* pByte = *aux; // aux points to a pointer to a byte.

  BYTE Byte = **aux;

  However, Barbara has mention that the refers to an array of bytes. This may allow us to make this work.

  Now, it it were defined as :

  DWORD XPTO(BYTE *aux)

  Then the equavalent C# code would be:

  Int32 XPTO([MarshalAs(UnmanagedType.LPArray, SizeConst= )] byte[] aux)

  Now, for

  DWORD XPTO(BYTE **aux)

  Then the equavalent C# code would be:

  Int32 XPTO([MarshalAs(UnmanagedType.LPArray, SizeConst= )] ref byte[] aux)

  However, both of these these open the question of how to fill in the SizeConst parameter.

  
  
  

• Ankith

  Mark Benningfield wrote:

  Try this: [DllImport("dllfilename")] public static extern Int32 XPTO(byte aux);

  Not quite. It's "DWORD XPTO(BYTE **aux)" and those two stars are important.

  With one star, I believe we could have used:

  [DllImport("dllfilename")] public static extern Int32 XPTO(ref byte aux);

  But for two stars, I think we'll need:

  [DllImport("dllfilename")] public static extern Int32 XPTO(ref IntPtr aux);

  with some extra manual code to get th ebyte out of the IntPtr.

  
  
  

• ralph.

  OK, let me give this a shot:

  Int32 XPTO([MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 1) out byte[] aux, out Int32 imagelength, out string type);

  
  
  

• Poma

  Hi Mark,

  The signature is (BYTE **aux) and so id does return a byte value.

  Regarding your second question : the function has a second value  to be returned "DWORD *imagelenght" that is giving me (correctly) the lenght of the photo data buffer.

   Function "DWORD XPTO(BYTE **aux,DWORD *imagelenght,char**type)"

   

  The 3rd gives the type of picture

   

  Thanks a lot!!

   

  Barbara

   

   

   

  
  

• Nigel Horne

  Sorry Mark, had to change the color of the bright green/blue text as it was hurting the eyes as well as being made as non readable! It's changed to red now
  
  

• wky

  Hello All.

  James:

  As I say, my C++ is pretty rusty, and getting worse the more I use C#, so I'll defer to you. As to the question of the length of the buffer:

  Barbara:

  This function returns a DWORD. Is it possible that a call to this function with zero or null specified for the buffer results in a return of the length required for that buffer, to be passed in the imagelength parameter See if you can find that out, and we'll try and make some more progress.

  
  
  

• jfyfe

   

  First : Thanks for all the help.

   

  What is returned by char** aux is a photo buffer pointer and I am not understanting how can construct the picture from this value.

  I have applied several functions in order to get this info from IntPtr (and return the picture) but without any kind of sucess! Can someone please help again with this one.

   

  Thanks for all the help given!

   

  Barbara

   

  
  

• qt1h00

  Hello All.

  ahmedilyas:

  Well, it just goes to show about "different strokes." For me, the brighter color was easier to read against the darker background. Are these colors easy to read

  private void Form1_VisibleChanged(object sender, EventArgs e) { if (this.Visible) MessageBox.Show("Visible"); }

  For me, the standard color for types from the Code editor is too dark against the dark background of the code sample outline. That's what in the above snippet. If it is readable for everyone else, I'll just stick with it.

  
  
  

• AdelioS

  Hello All.

  James:

  Well, I'd be the first to admit that my C++ is pretty rusty, but since **aux is a parameter, and parameters are R-values, doesn't that mean that **aux is a double indirection, meaning the data value at the address pointed to by the addressValue at the address pointed to by the pointer In this case, a byte

  
  
  

• Henk B

  Hi Mark,

  To have the buffer lenght I can just do something like "DWORD XPTO(null,DWORD *imagelenght,char**type)" And this is giving the lenght. DWORD has sucess/error codes. I have already tried with byte[] but nothing happens :( , it seems like is loosing information when passing from ** to [] ...

  Thanks,

  Barbara

  
  

• kevow

  Hello All.

  Barbara:

  In the C++ signature of the function, does it say (BYTE **aux), as in your OP, or (BYTE aux**)   As James pointed out, the stars are important, and where they are is equally important.

  BYTE **aux returns a byte value, whereas BYTE aux** is a pointer to a pointer that points to a byte array.  Also as James pointed out, getting the final address of the array is going to require a little fancy footwork, because I don't thing C# directly supports spanning pointer pointers.

  Let us know, and also, we'll need to know if the C++ code has any way of determining the size of the buffer, if it is one.

  HTH.

  
  
  

• shuQ

  yes that sample there is fine Mark - I meant you had this color:

  DllImport

   

  for myself, and other people, its too bright, unreadable and does hurt the eyes. :-)

  
  
  
• Unmanaged to managed code