How to pack the required bits of a structure in a char* ?

Question

Language : C++

I am working on Bit Packing (Extracting the required bits from the given data and packing them in a char*) . My code currently supports : - Integers - Characters - Strings

Now if I have to store the required bits of a structure, how should I go about it ? I mean what should I expect as input parameters for a generalized code w.r.t structures ?

The question may be vague and I am not expecting direct answers, even hints and pointers are appreciated.

Answer 1

Have a look at this for a very packed format or use an standard marshalling format such as json, xml, boost serialization,... and save yourself the grey hair.

Answer 2

As piotr already suggested: try using existing libraries to marshall.

However, since your already doing it yourself:
If your supported primitives are representable as bytes, then you shouldn't be bit packing (there might be some confusion about the term), otherwise consider using std::bitset.
Because C++ doesn't support reflection, there is no help in C++ to byte pack structures in a generic, safe and portable way, so be prepared to write a function per structure to pack each primitive and each member structure.
Overloading does help to call these functions in a generic way, so packing of containers (vector ...) can be done generically. However, if you want this, then prefer free functions over member functions, to avoid having a difference between packing primitives and packing structures.

Example:

void Pack(const MyStruct& str, Packer& pack)
{
  Pack(str.int1, pack);
  Pack(str.string1, pack);
  Pack(str.otherStruct, pack);
}