C# Lawyer: Address of a Managed Type

Can I Get the Address of a Managed Type?

    class Point 
    { 
        public int x;
        public int y; 
    }

    class A
    {
        unsafe static void Main()
        {
            Point pt = new Point();
            // Using fixed allows the address of pt members to be
            // taken, and "pins" pt so it isn't relocated.
            fixed (int* p = &pt.x)  //This is okay! 
            {
                *p = 1;
            }

            fixed (int* p = &pt)   //This won't compile.
            {
                //...
            }

        }
    }

Above code won't compile due to following error:

     Cannot take the address of, get the size of, or declare a pointer to a managed type ('something.Point')	

Conclusion: from above sample, you can see that you cannot get the address of a managed type! But you can point to value types of a class.

By the way, you might don't know much about "fixed" statement, I copied the definition of it from MSDN.

fixed Statement (C# Reference)

The fixed statement prevents the garbage collector from relocating a movable variable. The fixed statement is only permitted in an unsafe context. Fixed can also be used to create fixed size buffers.

    // assume class Point { public int x, y; }
    // pt is a managed variable, subject to garbage collection.
    Point pt = new Point();
    // Using fixed allows the address of pt members to be
    // taken, and "pins" pt so it isn't relocated.
    fixed ( int* p = &pt.x )
    {
        *p = 1; 
    }

See also

THIS POST IS PROVIDED "AS-IS" WITH NO WARRANTIES AND CONFERS NO RIGHTS. Build time: Sun 03/30/2008 . ©2007 Dalun Software. All rights reserved. Back to Article List