Bypassing C#'s type safeguards and storing an Integer in a String

Question

Have a look at the following code:

static void Main(string[] args)
{
    string s = null;
    string[] myArray = new string[1];

    { } // do something evil her         


        

Answer 1

One technique is using LayoutKind.Explicit to implement a union which can be used to reinterpret cast an arbitrary object to string. First box an int, then assign it to the object field of the union and then read out the string field.

[StructLayout(LayoutKind.Explicit)]
public struct Evil
{
    [FieldOffset(0)]
    public string s;

    [FieldOffset(0)]
    public object o;
}

string ReinterpretCastToString(object o)
{
    Evil evil=new Evil();
    evil.o=o;
    return evil.s;
}

void Main()
{
    string s = ReinterpretCastToString(1);

    if (s.GetType() == typeof(int))
    {
        Console.WriteLine("This should not happen!"); 
    }
}

This is most likely undefined behavior that may stop working at any time. Obviously you shouldn't use this in a real program.