C++ :: Creating Variable On Runtime - Message Decoding

I receive messages over a bus. Suppose there is a function to read the messages storing them into a struct defined as follows:

typedef struct
{
ULONG timestamp;
BYTE ID;
BYTE data_length;
BYTE data[8];
} MSG_FRAME;

Depending on the message ID different messages represent different values for one project.For example msg with ID 10 can include in the 8 bytes something like:

width: 6 bits
height: 6 bits
actpos: 12 bits
maxpos: 12 bits
minpos: 12 bits
range: 16 bits
total: 64 bits = 8 bytes

Printing the message is no big deal. But here comes the tricky part. I want to print out the specific information hidden in the 8 bytes. I can define the structures for every msg ID and compile the program with this "special" header file, but I want to do it during runtime of the program, loading the information regarding the msgs, because i can have different projects where the information for different msg IDs can differ.

I've a non-C file, where basically all the information is written. Lets stay frame named

GetStatus{
bit 0 - 7 width
bit 8 - 15 height
.
.
}
etc.

How to read it on runtime and decode the messages? On runtime I'm not able to create variables and structures anymore!