Question

I’ve seen a number of methods to copy a byte[] to a struct, and vise-versa. However, I was wondering if it was possible to cast the byte[] pointer to a struct (like you do in C)..

I want to be able to cast a byte[] to a struct, make changes to the struct, and have the changes automatically appear in the byte[].

Thanks,
reza

Answer 1

You just cast the pointer (sometimes you need to go via void* in the middle):

struct Foo
{
    public int Bar;
}
static unsafe void Main()
{
    byte[] buffer = new byte[10];
    fixed (byte* untyped = buffer)
    {
        var typed = (Foo*)untyped;
        typed[0].Bar = 123;
    }
    // buffer has the changes
}

If you need to offset into the buffer, then use byte* untyped = &buffer[offset].

If you want a raw struct pointer, then:

fixed (byte* ptr = buffer)
{
    var typed = (Foo*)ptr;
    Foo* foo = &typed[0];
    foo->Bar = 123;
}

However, note that you can’t pass a Foo* to methods expecting a Foo or ref Foo.