How to convert a sbyte[] to byte[] in C#?

Question

I've got a function which fills an array of type sbyte[], and I need to pass this array to another function which accepts a parameter of type byte[].

Can I convert it nicely and quickly, without copying all the data or using unsafe magic?

Answer 1

Yes, you can. Since both byte and sbyte have the same binary representation there's no need to copy the data. Just do a cast to Array, then cast it to byte[] and it'll be enough.

sbyte[] signed = { -2, -1, 0, 1, 2 };
byte[] unsigned = (byte[]) (Array)signed; 

Answer 2

You will have to copy the data (only reference-type arrays are covariant) - but we can try to do it efficiently; Buffer.BlockCopy seems to work:

    sbyte[] signed = { -2, -1, 0, 1, 2 };
    byte[] unsigned = new byte[signed.Length];
    Buffer.BlockCopy(signed, 0, unsigned, 0, signed.Length);

If it was a reference-type, you can just cast the reference without duplicating the array:

    Foo[] arr = { new Foo(), new Foo() };
    IFoo[] iarr = (IFoo[])arr;
    Console.WriteLine(ReferenceEquals(arr, iarr)); // true

Answer 3

If you are using .NET 3.5+, you can use the following:

byte[] dest = Array.ConvertAll(sbyteArray, (a) => (byte)a);

Which is, I guess effectively copying all the data.

Note this function is also in .NET 2.0, but you'd have to use an anonymous method instead.