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unsigned char ** equivalent in c# and have to write the return value in a file

I have to call a win32 dll function

int func1(int arg1, unsigned char *arg2, int *arg3);

and i wrote wrapped c# as

public extern int fuc1(int arg1, out IntPtr arg2, out IntPtr arg3);

The arg2 has to allocate 2048 bytes and send it to the win32 dll. I’ll get arg2 and arg3 as output.

how can i declare in c# test application as well as c# wrapper. am i doing it right ?

Answer 1

byte in C# is unsigned 8-bit int. byte[] is an array of them. To get a pointer to this array, use:

 var myArray = new byte[2048];
 fixed(byte* arg2 = myArray)
 {
      // use arg2
 }

or:

 var myArray = new byte[2048];
 GCHandle pinnedRawData = GCHandle.Alloc(myArray, GCHandleType.Pinned);
 try
 {  
    // Get the address of the data array
    IntPtr pinnedRawDataPtr = pinnedRawData.AddrOfPinnedObject();
 }
 finally
 {
    // must explicitly release
    pinnedRawData.Free(); 
 } 

Alternatively, if the called function will not cache a pointer to the array, you can simply do this:

 public static extern int fuc1(int arg1, [In,Out] byte[] arg2, ref int arg3);

 var arg1 = 0;
 var arg2 = new byte[2048];
 int arg3 = 42; // If this value won't be used, you can skip initializing arg3 and mark arg3 as out instead of ref (of course, this is pedantic and extraneous, and C# shouldn't even have 'out' as a keyword)

 func1(arg1, arg2, ref arg3);

P/Invoke will pin it automatically.

MSDN Marshaling Arrays of Types

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