casting - c++ union in multiple files -

i'm sorry long, little complicated explain.

we had hand in homework following program (much simplified here):

some type of structure (class/struct) representing physical block of data (just char[1024])
two types of logical partitioning of block

for example:

struct p {   char[1024] } struct l1 {   int num;   char name[20]; } struct l2 {   int num;   char type[10];   char filler[400];   bool flag; }

the obvious thing me have union

union {   p phy;   l1 logi1;   l2 logi2; }

but problem part of specification (the part cut out simplify it) physical stuff in separate file logical stuff.

so question is: there way add fields union (i assume not) or way have functions in 'physical' file accept 'logical' blocks , use them raw blocks?

i hope clear.

p.s. due , solved reinterpret_cast. wondering if there more elegant way.

what can create 2 unions. long don't interchange them fine.

Assebmley