🚀 go-pugleaf

In article <8908141613.AA23693@dsys.ncsl.nist.gov> rbj@DSYS.NCSL.NIST.GOV (Root Boy Jim) writes:
>? From: chatty%FRLRI61.BITNET@cunyvm.cuny.edu
>
>? I just discovered that an empty class has a non-null size. Is that
>? intentional?  If it is, what are those 2 bytes for?  Until now, I
>? thought having an empty base class was for free. I am disappointed.
>
>? I use g++ 1.35.1- on a Sun3 running OS 3.5.
>
>Just a bit of speculation here. I hope you don't think all that
>whiz-bang object-oriented stuff comes for free. Most likely those two
>bytes are a pointer into some table telling you what class the thing
>really is. Remember that when deriving one class from another, some
>means of dynamically determining to which class an object belongs
>must be provided. The higher level the language, the farther you
>get from what the thing really is. Live with it.

Well, consider it padding... (On a vax, with 1.35.0 anyway...)
I have a simple class like:

class oXdisplay {
	Display *dpy;
	dpy() { ... }
	~dpy() { ... }
};

And it does the Right Thing.  It consumes a whole four bytes of memory per
object.  The Display* alone takes four bytes...

But I DID find it interesting that an empty class on my machine did take
a byte; just one. A class with just a char in it also took one byte.
And a class with an int in it took 4 bytes.

Note: due to memory alignments, all classes eat four bytes of memory
apiece.

The code, just if you want to see it is around line 729 of stor-layout.c
in 1.35.0 and looks like:

  /* C++: do not let empty structures exist.  */
  if (const_size == 0 && var_size == 0)
    const_size = size_unit;

So g++ does not need or use it, the question to the writers (Michael???)
why force it up to one?