Question

Consider the following code:

using System;
using System.Runtime.InteropServices;

namespace Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            const string test = "ABCDEF"; // Strings are immutable, right?
            char[] chars = new StringToChar{str=test}.chr;
            chars[0] = 'X';

            // On an x32 release or debug build or on an x64 debug build, 
            // the following prints "XBCDEF".
            // On an x64 release build, it prints "ABXDEF".
            // In both cases, we have changed the contents of 'test' without using
            // any 'unsafe' code...

            Console.WriteLine(test);
        }
    }

    [StructLayout(LayoutKind.Explicit)]
    public struct StringToChar
    {
        [FieldOffset(0)]
        public string str;
        [FieldOffset(0)]
        public char[] chr;
    }
}

By running this code, we are able to change the contents of a string without an exception occuring. We did not have to declare any unsafe code to do so. This code is clearly very dodgy!

My question is simply this: Do you think that an exception should be thrown by the code above?

[EDIT1: Note that other people have tried this for me, and some people get different results – which isn’t too suprising given the nastyness of what I’m doing… ;)]

[EDIT2: Note that I’m using Visual Studio 2010 on Windows 7 Ultimate 64 bit]

[EDIT3: Made the test string const, just to make it even more dodgy!]

Answer 1

My vote’s on making FieldOffset unsafe.