Clean way to keep all private variables in class ( private struct, pimpl idiom )

[atomic]

Maybe I wrong name this post, I thought about a large number of private variables as you say > 15.
Sometimes this "data" structure can eliminated conflict of names and you do not need create prefix to variables like _m or similar.
Thanks,

[Alundra]

Coding rules are important, and that's important to keep these rules during all the development.
For class member, keep the "m_" or just "m" front of variables.
Use "Set", "Get", "Count" and "Compute" in function's names.

[stampede]

pimpl is only really needed if you need platform-independent data or wanting to hide a lib data.

Or you want to shorten the rebuild time (change in the class internals will require to rebuild only the class.cpp file). Very useful in large projects IMHO.