Fixed wide string marshaling on UTF-32 platforms.

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -189,7 +189,15 @@ namespace CppSharp.Generators.CSharp
 
             if (Equals(encoding, Encoding.Unicode) ||
                 Equals(encoding, Encoding.BigEndianUnicode))
-                return string.Format("Marshal.PtrToStringUni({0})", varName);
+            {
+                if (Context.Driver.TargetInfo.WCharWidth == 16)
+                    return string.Format("Marshal.PtrToStringUni({0})", varName);
+
+                const string encodingName = "System.Text.Encoding.UTF32";
+                return string.Format(
+                    "CppSharp.Runtime.Helpers.MarshalEncodedString({0}, {1})",
+                    varName, encodingName);
+            }
 
             throw new NotSupportedException(string.Format("{0} is not supported yet.",
                 Context.Driver.Options.Encoding.EncodingName));

src/Runtime/Helpers.cs

@@ -1,11 +1,24 @@
 using System;
 using System.Collections.Concurrent;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace CppSharp.Runtime
 {
     public static class Helpers
     {
+        public static string MarshalEncodedString(IntPtr ptr, Encoding encoding)
+        {
+            var size = 0;
+            while (Marshal.ReadInt32(ptr, size) != 0)
+                size += sizeof(int);
+
+            var buffer = new byte[size];
+            Marshal.Copy(ptr, buffer, 0, buffer.Length);
+
+            return encoding.GetString(buffer);
+        }
+
 #if WINDOWS
         [DllImport("msvcrt.dll", EntryPoint = "memcpy", CallingConvention = CallingConvention.Cdecl)]
 #else