What should be the sizeof a class considering that the class does not have
any data members(only methods). I know that if I have virtual functions, the
sizeof returns the size of the vptr, but what if I don't have these either?

A simple test using VC++ returns 1 from the sizeof, what is this the size of?

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In article <6t99t2$ocb$1@nnrp1.dejanews.com>,
  trujillom@lincom.com wrote:
> What should be the sizeof a class considering that the class does not have
> any data members(only methods). I know that if I have virtual functions, the
> sizeof returns the size of the vptr, but what if I don't have these either?
>
> A simple test using VC++ returns 1 from the sizeof, what is this the size of?

All data types are required to have a size of at least one byte.
But don't rely on "sizeof" math:
    class A {}; // Size is 1
    class B : public A { char x[3]; }; // Size might not be 4
Some systems will be "smart" enough to make sizeof(B)==3, despite being
derived from class A.

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Please reply in USENET only, sorry.

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trujillom@lincom.com wrote in message <6t99t2$ocb$1@nnrp1.dejanews.com>...
>What should be the sizeof a class considering that the class does not have
>any data members(only methods). I know that if I have virtual functions,
the
>sizeof returns the size of the vptr, but what if I don't have these either?
>
>A simple test using VC++ returns 1 from the sizeof, what is this the size
of?

1 is the size of the smallest possible class object. The size is non-zero so
that arrays of the class are meaningful with each element having a different
address.

--
     The Klingon's favorite food was named by the first earthling to see it
      David Sachs - Fermilab - MS369 - PO Box 500 - Batavia, IL 60510
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trujillom@lincom.com wrote:
>
> What should be the sizeof a class considering that the class does not have
> any data members(only methods). I know that if I have virtual functions, the
> sizeof returns the size of the vptr, but what if I don't have these either?
>
> A simple test using VC++ returns 1 from the sizeof, what is this the size of?

Each time you create an object of that type, it must be given a unique
address. Since the smallest difference between two non-equal addresses
is 1, even an empty object uses up at least 1 byte of space.
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<trujillom@lincom.com> wrote:
>What should be the sizeof a class considering that the class does not have
>any data members(only methods). I know that if I have virtual functions, the
>sizeof returns the size of the vptr, but what if I don't have these either?

For an exploration of this question, see

  http://www.cantrip.org/emptyopt.html

--
Nathan Myers
ncm@nospam.cantrip.org  http://www.cantrip.org/
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trujillom@lincom.com wrote:

> What should be the sizeof a class considering that the class does not have
> any data members(only methods). I know that if I have virtual functions, the
> sizeof returns the size of the vptr, but what if I don't have these either?
>
> A simple test using VC++ returns 1 from the sizeof, what is this the size of?

Size of object, of course ;) Standard says, that objects of empty class shall
have nonzero size. There is good reason for this: to avoid aggregation members
aliasing. If size is zero, then pointers to 2 sequential empty subobjects would
be same.
See Nathan Myers article in DDJ (Dr. Dobb's Journal) #268, August 1997 for
discussion about empty members and their optimization.
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