Can I load header(.h) file to get struct at runtime? (C++) - c++

Question

I want to build a C++ program, a Shared Memory Monitor/Interceptor/Recorder/Playbacker.
Basically, I have no problem with those functions I want to implement.
Now my main problem is I want to let this program have ability to load a lot of different ICD file, so I can view different Shared Memory just load that Shared Memory use ICD header file, so I don't need to include that ICD file and re-build this program.
Example ICD Header File A (A.h):
struct StructA
{
bool btState;
float X_Pos;
float Y_Pos;
float Rotate;
};
Example ICD Header File B (B.h):
struct StructB
{
int systemState;
int missionState;
};
So, when my program startup, it will show a File Selector Dialog like many others program, then user can select a Header File, when select done and write this Shared Memory used name to input field, the UI will show about this struct content.
Like(when A.h loaded):
btState false
X_Pos 0.04568f
Y_Pos 456.556f
Rotate 25.258f
So, should I load these file like text file, and build a class to make some string cut/analysis, or use a C++ compiler to compile this file at run-time ?
Tanks.

Answer 1

Header files cannot be replaced at runtime, since they are evaluated at the first step of the compilation of the source code to a fixed binary.
What you are looking for is the factory pattern.
Create a (pure virtual) interface class ICD. This should contain all common data and member functions. From this you can derive the classes A_ICDand B_ICD` (content from your header A and B) .
From given user input you can decide, if you create an object form A_ICD or B_ICD.
The source code using the object of A_ICD or B_ICD uses only the interface class ICD and thus does not need to know, which class is instantiated.

Answer 2

If you actually want a run-time definition of data structure, ANY arbitrary structure, don't use C code. You'd have to parse it on your own or use libraries to parse that and C isn't good for data description. Use domain documents like .xml and a library to parse that, or specialized data-describing languages, e.g OpenDDL.
PS. At work we were solving similar problem as a playback program for network interactions. The program recompilation every time when protocol had changed even slightly would have been unacceptable, but only source of data was indeed a header file used to build communicating programs. A simple parser of struct definitions had been made.
Then program would just remember sizes and offsets of the fields after parsing sequences, making assumptions about memory layout for reading fields one by one out of binary file. It's a highly unportable solution born out of lack of manpower to create intermediate development documentation (protocol documentation in machine-readable form). As it was a network protocol between incompatible platforms, problems of aligning fields and byte order already were solved, with shared memory it would be an existing problem.