Question

The MSDN document that I am trying to follow is located here. Basically I am trying to figure out in C# how to read that pointer into a list of the DHCP_OPTION_DATA structures.

I have the following code but I don’t think that it is the proper way to do this.

DHCP_OPTION_ARRAY optionArray = (DHCP_OPTION_ARRAY)Marshal.PtrToStructure(options, typeof(DHCP_OPTION_ARRAY));
List<DHCP_OPTION> allOptions = new List<DHCP_OPTION>();
for (int i = 0; i < optionArray.NumElements; i++) {
    DHCP_OPTION option = (DHCP_OPTION)Marshal.PtrToStructure(optionArray.Options, typeof(DHCP_OPTION));
    allOptions.Add(option);
    optionArray.Options = (IntPtr)((int)optionArray.Options + (int)Marshal.SizeOf(option));
}

Since I can’t Marshal the pointer into a generic list collection I tried this way. My problem is that I am getting skewed results based on how much I increase the IntPtr to. Initially I was doing this.

optionArray.Options = (IntPtr)((int)optionArray.Options + (int)Marshal.SizeOf(typeof(DHCP_OPTION_DATA)));

However, I then realized that the next element would be located after the size of the actual option.

So the question still remains, how do I Marshal a Ptr to a list of structures?

EDIT 1

I posted the wrong article it is fixed now.

EDIT 2

Although both answers were great, I chose the answer to my problem because it addressed my lack of understanding of how the data was being handled on the back end of marshaling the information.

Answer 1

Is the first option object you get correct?
If so, the reason for the rest being skewed most likely is the alignment of the structure.

You could try to find the correct alignment, for example:

var offset = (int)Marshal.SizeOf(typeof(DHCP_OPTION_DATA));
var alignment = 4; 
var remainder = offset % alignment;
if(remainder != 0)
    offset += alignment - remainder;

optionArray.Options = (IntPtr)((int)optionArray.Options + offset);