why is size of object of empty class is 1 byte

[ishekara]

Hi all,

An object of a class A which has no member variables and no member
functions, still the size of the object is 1 byte, if there is a byte member
variable then also the size of the object is 1 byte. Could anyone tell me
the reason behind this.

Thanks
ishekara

 

[Sharad Kala]

Hi all,

An object of a class A which has no member variables and no member
functions, still the size of the object is 1 byte, if there is a byte member
variable then also the size of the object is 1 byte. Could anyone tell me
the reason behind this.

http://www.research.att.com/~bs/bs_faq2.html#sizeof-empty

Sharad

 

[Shan]

An object of a class A which has no member variables and no member

functions, still the size of the object is 1 byte, if there is a byte member
variable then also the size of the object is 1 byte. Could anyone tell me
the reason behind this.

There is no requirement in the C++ standard that an empty object should
have one byte of memory aoocupied. It is purely based on the
implementation.

 

[Mike Hewson]

Hi all,

An object of a class A which has no member variables and no member
functions, still the size of the object is 1 byte, if there is a byte member
variable then also the size of the object is 1 byte. Could anyone tell me
the reason behind this.

Thanks
ishekara

So that any and all instantiations ( objects ) of the empty version of
class A will have distinct addresses ( evidently at least one byte away
). Thus pointers, references et al of distinct objects will be different.

 

[Mike Hewson]

There is no requirement in the C++ standard that an empty object should
have one byte of memory aoocupied. It is purely based on the
implementation.

Sorry
but, not if it's conforming ( ISO/IEC 14882 p.149 ):

9 Classes [class]
..
..
..
3 Complete objects and member subobjects of class type shall have
nonzero size. ...

 

[Shan]

3 Complete objects and member subobjects of class type shall have

nonzero size. ...

Sorry, i missed that....And thanks )

 

[Mike Hewson]

Sorry, i missed that....And thanks )

Actually I love the way English, as a common language, divides us.

If I say "class X is of size 10 bytes", does that imply that "one byte
of memory occupied". Well yes, it does, but I just didn't mention the
other nine.

 

[owl ling]

because a objeect's size can not be 0, it is a instance.
but sonetime,a class's size may be 0 when the class will haven't a
instance at anytime.

to read a words what was called "countting object in c++".by meyers.
you will get more things.
good luke

 

[Mike Wahler]

There is no requirement in the C++ standard that an empty object should
have one byte of memory aoocupied.

True, but it does require that it have a nonzero size.

It is purely based on the
implementation.

Yes, the exact nonzero size is implementation-defined.

-Mike