使用基于头类型的字节数组初始化struct

I have several structs in my file. I want to pass a byte array and initialize the the struct. I have tried struct to byte array conversion and vice versa but I am getting errors like "Attempted to read or write protected memory". So I thought passing byte array to initialize the struct might be more efficient. My problem is that one part of structure is dependent of first byte type. So how do I assign another structure to it?I have several structs in my file. I want to