How do I convert an IntPtr to a Stream?

Question

class Foo
{
   static bool Bar(Stream^ stream);
};

class FooWrapper
{
   bool Bar(LPCWSTR szUnicodeString)
   {
       return Foo::Bar(??);
   }
};

MemoryStream will take a byte[] but I'd like to do this without copying the data if possible.

Answer 1

You can avoid the copy if you use an UnmanagedMemoryStream() instead (class exists in .NET FCL 2.0 and later). Like MemoryStream, it is a subclass of IO.Stream, and has all the usual stream operations.

Microsoft's description of the class is:

Provides access to unmanaged blocks of memory from managed code.

which pretty much tells you what you need to know. Note that UnmanagedMemoryStream() is not CLS-compliant.

Answer 2

If I had to copy the memory, I think the following would work:

static Stream^ UnicodeStringToStream(LPCWSTR szUnicodeString)
{
   //validate the input parameter
   if (szUnicodeString == NULL)
   {
      return nullptr;
   }

   //get the length of the string
   size_t lengthInWChars = wcslen(szUnicodeString);  
   size_t lengthInBytes = lengthInWChars * sizeof(wchar_t);

   //allocate the .Net byte array
   array^ byteArray = gcnew array(lengthInBytes);

   //copy the unmanaged memory into the byte array
   Marshal::Copy((IntPtr)(void*)szUnicodeString, byteArray, 0, lengthInBytes);

   //create a memory stream from the byte array
   return gcnew MemoryStream(byteArray);
}