IntPtr and avoiding unsafe code

Question

I have an external library that takes an IntPtr. Is there any safe way to do this...

int BytesWritten = 0;
Output.WriteBytes(buffer, new IntPtr(&BytesWritten));

...without having to use 'unsafe' code? I'm not that familiar with IntPtrs, but I'd like to do something like this:

fixed int BytesWritten = 0;
Output.WriteBytes(buffer, IntPtr.GetSafeIntPtr(ref BytesWritten));

...in such a way that I don't need to compile with /unsafe.

I can't change the WriteBytes function, it's an external function.

It seems like there should be some sort of cast between 'ref int' and IntPtr, but I have not had luck finding it.

Answer 1

I assume that Output.WriteBytes is a [DllImport] method. Can you post the declaration?

You should be able to avoid the pointer by declaring the last parameter as out int instead of IntPtr -- let the P/Invoke marshaller do the rest.

Answer 2

Yes, there is. You can use P/Invoke for your code. It will create the pointer for you automagically. Something like this:

[DllImport("yourlib", SetLastError=true)]
static extern bool WriteBytes(
    [MarshalAs(UnmanagedType.LPArray)]
    byte [] buffer,
    ref int BytesWritten);

(I added the array as a bonus). More info on P/Invoke can be found, with gazillion examples, at pinvoke.net.

Each parameter above can take out, in and ref. Out and ref parameters are translated as pointers, where an ref-parameter is two-way.