Using readExact with a struct containing a dynamic array

[Charles Hixson]

I want to create a struct like this:
struct test
{  int  item 1;
    int  item 2;
    int  dataLen;
    ubyte[]  data;
}

Then I want to read & write the structure using readExact and 
writeExact.  Can I do this (somehow?) or do I need to do the 
reads/writes separately for each piece?

I'm sure I could just declare data large enough to hold all cases, but 
that gets wasteful over time.  I could just use a buffered file, so that 
doing the reads/writes separately would be cheaper.  But if I'm using an 
ordinary file is there a way to do this using readexact/writeexact? 
(I.e., if I wrote/read the proper number of bytes, would I get the 
correct data, and is the proper number == 3*int.sizeof + data.length?)

I feel like I could write lots of tests, but each one would just prove 
"That's not the way to do it".