Question

I have a struct that looks something like this:

[StructLayout(LayoutKind.Sequential)]
public struct in_addr {
    public Anonymous1 S_un;

    [StructLayoutAttribute(LayoutKind.Explicit)]
    public struct Anonymous1 {
        [FieldOffsetAttribute(0)]
        public Anonymous2 S_un_b;

        [FieldOffsetAttribute(0)]
        public Anonymous3 S_un_w;

        [FieldOffsetAttribute(0)]
        public uint S_addr;
    }

    [StructLayoutAttribute(LayoutKind.Sequential)]
    public struct Anonymous2 {
        public byte s_b1;
        public byte s_b2;
        public byte s_b3;
        public byte s_b4;
    }

    [StructLayoutAttribute(LayoutKind.Sequential)]
    public struct Anonymous3 {
        public ushort s_w1;
        public ushort s_w2;
    }

    public in_addr(byte[] address) {
        S_un.S_addr = (uint)BitConverter.ToInt32(address, 0);

        S_un.S_un_b.s_b1 = address[0];
        S_un.S_un_b.s_b2 = address[1];
        S_un.S_un_b.s_b3 = address[2];
        S_un.S_un_b.s_b4 = address[3];

        S_un.S_un_w.s_w1 = 0;
        S_un.S_un_w.s_w2 = 0;
    }
}

When I try to create a new instance of this struct, every byte field is set to 0.

in_addr temp = new in_addr(bytes);

I’ve stepped through the struct’s constructor and verified that the bytes are indeed getting assigned to the fields. But when I step out of the constructor and check the value of temp, everything is 0.

What’s causing this?

Answer 1

Because of these lines:

S_un.S_un_w.s_w1 = 0;
S_un.S_un_w.s_w2 = 0;

They are mapped to your 4 bytes via

[FieldOffsetAttribute(0)]
public Anonymous2 S_un_b;

[FieldOffsetAttribute(0)]
public Anonymous3 S_un_w;