Re: Another C# marshaling question
- From: "Laurent" <mournblade@xxxxxxx>
- Date: Tue, 29 Nov 2005 14:01:00 +0100
Hi Nicholas,
Thank you for your answer, it works !!! I can access my function and the
returned value is as expected.
But I still have a little problem... this part of code doesn't work "as
it":
for (int index = 0; index < outNumber; index++)
{
// Get the pointer of the location in memory.
IntPtr elementPointer = new IntPtr(outStructure.ToInt64() + (index *
Marshal.SizeOf(typeof(FF_Struct))));
// Now marshal that value.
outStructs[index] = Marshal.PtrToStructure(elementPointer,
typeof(FF_Struct));
}
In fact, the first line is OK and the others have not been read
correctly. When I debug the code, Marshal.SizeOf(typeof(FF_Struct)) = 32. I
wrote the part of memory I have read into a binary file and examinated it
with Hex Editor. The size of my structure is 29. When I manually put this
value into your code, it works perfectly.
I think something is wrong with my FF_Struct class definition, but I
don't know why. I'm sure the size of the char arrays is OK. Prehaps the
problem comes from the '\0' terminated string ??? Do you have any clue ?
Thanks anyway for your help, you taught me a lot of stuffs today ! :)
Laurent
"Nicholas Paldino [.NET/C# MVP]" <mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx> a écrit
dans le message de news: O7Gnt6D9FHA.4076@xxxxxxxxxxxxxxxxxxxxxxx
> Laurent,
>
> You are going to have to manually marshal the structure. Your
> structure declaration needs to be changed:
>
> [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi)]
> public class FF_Struct
> {
> public int index;
> [MarshalAs(UnmanagedType.ByValTStr, SizeConst = FF_ID_LEN)]
> public string numeroCommande;
> [MarshalAs(UnmanagedType.ByValTStr, SizeConst = FF_DATETIME_LEN)]
> public string dateCommande;
> }
>
> Declaring as a class will tell the CLR that it can re-arrange the order
> of the fields as it wishes, which is not what you want in this case.
>
> You will also have to change your function declaration to:
>
> [DllImport("FF_myDLL.dll")]
> public static extern int FF_Function(
> IntPtr inInstance,
> [MarshalAs(UnmanagedType.LPTStr)]
> string date,
> ref IntPtr outStructure,
> ref int outNumber
> );
>
> Then, what you have to do on return is marshal the array, like so:
>
> // Allocate the array.
> FF_Struct[] outStructs = new FF_Struct[outNumber];
>
> // Cycle through unmanaged memory, and marshal.
> for (int index = 0; index < outNumber; index++)
> {
> // Get the pointer of the location in memory.
> IntPtr elementPointer = new IntPtr(outStructure.ToInt64() + (index *
> Marshal.SizeOf(typeof(FF_Struct))));
>
> // Now marshal that value.
> outStructs[index] = Marshal.PtrToStructure(elementPointer,
> typeof(FF_Struct));
> }
>
> The only problem here is that you have to figure out how to release the
> memory that was allocated for the structure. The function is allocating
> it, but you aren't handling that in this situation.
>
> Hope this helps.
>
>
> --
> - Nicholas Paldino [.NET/C# MVP]
> - mvp@xxxxxxxxxxxxxxxxxxxxxxxxxxx
>
>
> "Laurent" <mournblade@xxxxxxx> wrote in message
> news:u210%23zD9FHA.1484@xxxxxxxxxxxxxxxxxxxxxxx
>> Hi again,
>>
>>
>>
>> I created a thread some days ago, while I was trying to access a C++
>> DLL using my C# program. First of all, I want to thanks all the guys who
>> helped me. But I still have a problem... My C++ DLL has a function which
>> has the following prototype:
>>
>> long FF_Function(void* inInstance, char* inDate, FF_Struct**
>> outStructure, long* outNumber);
>>
>> The structure has the following prototype:
>>
>> struct FF_Struct
>> {
>> long m_Index;
>> char m_ID[FF_ID_LEN];
>> char m_Date[FF_DATETIME_LEN];
>> };
>>
>>
>> I know that the function should return me an array of FF_Struct, and
>> that the parameter outNumber has the number of elements stored in the
>> FF_Struct array. Now, I'm tring to translate it in C#, and here is what I
>> did (which does not work, of course):
>>
>>
>> public class FF_AO_OrderList
>> {
>> public int index;
>> [MarshalAs(UnmanagedType.ByValTStr, SizeConst = FF_ID_LEN)]
>> public string numeroCommande;
>> [MarshalAs(UnmanagedType.ByValTStr, SizeConst = FF_DATETIME_LEN)]
>> public string dateCommande;
>> }
>>
>>
>> [DllImport("FF_myDLL.dll")]
>> public static extern int FF_Function
>> (
>> IntPtr inInstance,
>> [MarshalAs(UnmanagedType.LPTStr)]
>> string date,
>> out FF_Struct[] outStructure,
>> out int outNumber
>> );
>>
>>
>> I can access the function, but it returns me an error message ("The
>> parameters specified for the interface are incorrect."). I don't know how
>> to deal with this structure and its double pointer. Even in unsafe mode
>> (then I use a FF_Struct** parameter), I have the same problem.
>>
>>
>> Does anyone knows what I'm missing ? I'd greatly appreciate some help,
>> as I'm completely out of ideas... Thanks !!!!
>>
>>
>>
>> Laurent
>>
>
>
.
- References:
- Another C# marshaling question
- From: Laurent
- Re: Another C# marshaling question
- From: Nicholas Paldino [.NET/C# MVP]
- Another C# marshaling question
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