address of byte array

I am a C# beginner so I don't know the C# syntax that good.
I have a CF app that manipulates a bunch of data in a byte array.
I need to pass the address of the start of the array as a DWORD
(C# uint) to my unmanaged code function with pinvoke. The unmanaged
code I know works and my app works with the data correctly.
I have made other pinvoke calls and I understand it to some extent.
I can't seem to get the syntax correct for the address of the byte array.
Is there a such thing as a "cast" like in C where I can coheres the start of
the array to a uint?
I tried all kind of permutation of "ref" "&" and get nothing but syntax
errors.

Unfortunately there is a bug in GCHandle implementation on CF. IF you pin an
array you will get a pointer to a control structure instead of array data.
In particular for simple 1-dim arrays it will be address of array[-1]
holding numelements. To get a pointer to a real address it will need to be
incremented by 4.

"Daniel Petersson" <dape@isbit.com> wrote in message
news:268FBA49-44CE-4A19-B030-9E14E29E3F00@microsoft.com...
> To get the adress of an object for interop you use the IntPtr type
together
> with GCHandle.
>
> // an array of bytes
> byte[] bytes = new byte[]{ 1,2,3,4,5 };
>
> // pin array during interop operation and to get the address
> GCHandle pinnedArray = GCHandle.Alloc( bytes, GCHandleType.Pinned );
>
> // do funky interop call
> Win32.NativeCallThatNeedAdressOfArray( pinnedArray.AddrOfPinnedObject );
>
> // free the handle
> pinnedArray.Free();

Arrays are referenced objects and as such are marshalled by pointer. So if
you have a function that takes e.g. LPBYTE, the corresponding C# declaration
would have byte[] and not ref byte[]. Note that since pointer types are
currently 4 byte, you can have
[DllImport]
extern static void MyFunc(byte[] parm);

calling into

void WINAPI MyFunc(DWORD parm)
{
LPBYTE arr = (LPBYTE)parm;
...
}

In this case the address of the first array element will be passed
downstream

"A. User" <dve@byby.com> wrote in message
news:OaP5OtxCEHA.3804@TK2MSFTNGP09.phx.gbl...
> I am a C# beginner so I don't know the C# syntax that good.
> I have a CF app that manipulates a bunch of data in a byte array.
> I need to pass the address of the start of the array as a DWORD
> (C# uint) to my unmanaged code function with pinvoke. The unmanaged
> code I know works and my app works with the data correctly.
> I have made other pinvoke calls and I understand it to some extent.
> I can't seem to get the syntax correct for the address of the byte array.
> Is there a such thing as a "cast" like in C where I can coheres the start
of
> the array to a uint?
> I tried all kind of permutation of "ref" "&" and get nothing but syntax
> errors.
>
>
>

to answer your question:

unsafe void call(byte[] values)
{
fixed(byte* pvalue = &values[0])
callNative((uint) pvalue);
}
or something like that ?

anyway I do prefer Alex Feyman's trick of a proper interop definition

[DllImport(mylib)]
static extern void myfunc(byte[] array);


"Daniel Petersson" <dape@isbit.com> wrote in message
news:268FBA49-44CE-4A19-B030-9E14E29E3F00@microsoft.com...
> To get the adress of an object for interop you use the IntPtr type
together
> with GCHandle.
>
> // an array of bytes
> byte[] bytes = new byte[]{ 1,2,3,4,5 };
>
> // pin array during interop operation and to get the address
> GCHandle pinnedArray = GCHandle.Alloc( bytes, GCHandleType.Pinned );
>
> // do funky interop call
> Win32.NativeCallThatNeedAdressOfArray( pinnedArray.AddrOfPinnedObject );
>
> // free the handle
> pinnedArray.Free();