public unsafe IntPtr GetSomeString()
        {
            string someString = "sample string";
            sbyte[] buffer = new sbyte [someString .Length + 1];

            for (int i = 0; i < someString .Length; i++)
            {
                buffer[i] = (sbyte) someString [i];
            }

            buffer[someString .Length] = 0;

            fixed (sbyte * p = buffer)
            {
                return new IntPtr(p);
            }
        }