Are methods of a class created only once for all objects or for each object
as its own copy of its methods?
It seems that I can only access an object method's address using :: so if I
have a class with method func and I want its address I would do
&someClass::som eFunc which seems to imply that there is only one function
per class(and hence for all instantiations of that class)... when I create a
very large array of objects of that class it seems to back this up as the
file size does not change much...
I just want to be sure that there is no need to deal with static members and
stuff for no to make sure I optimize size if the compiler handles it
automatically(w hich I hope it does)? i.e. there is virtually no difference
between these two classes
class A
{
int x;
public:
void func(int y) { x = y; }
}
and
class B
{
int x;
public:
static void func(B &b, int y) { b.x = y; }
}
a.func(1);
and
b.func(b, 1);
should produce the exact same code? (or very very close?) I'm hoping that
the compiler internally handles class A as class B or maybe even better. The
reason is that simply class B has only 1 func even if I do something like B
b[10000]; while I'm not sure about class A.. if I do A a[10000] if it
creates 10000 copies of func or not. Though I don't see any reason why this
would happen and all my "tests" say it doesn't... I just want to make sure
so.
Thanks,
Jon
11  1525 
Jon Slaughter wrote: Are methods of a class created only once for all objects or for each object
as its own copy of its methods?
The former.
[snip]
I just want to be sure that there is no need to deal with static members and
stuff for no to make sure I optimize size if the compiler handles it
automatically(w hich I hope it does)? i.e. there is virtually no difference
between these two classes
class A
{
int x;
public:
void func(int y) { x = y; }
}
and
class B
{
int x;
public:
static void func(B &b, int y) { b.x = y; }
}
The above implies sizeof(A) == sizeof(B) == sizeof(int). I.e., each
class should be the size of an int.
a.func(1);
and
b.func(b, 1);
should produce the exact same code? (or very very close?)
I expect they would be quite close, but it doesn't matter - the number
of copies of the member function does not increase as objects are
constructed.
I'm hoping that
the compiler internally handles class A as class B or maybe even better. The
reason is that simply class B has only 1 func even if I do something like B
b[10000]; while I'm not sure about class A.. if I do A a[10000] if it
creates 10000 copies of func or not.
It doesn't.
Best regards,
Tom
Thomas Tutone wrote: Jon Slaughter wrote: Are methods of a class created only once for all objects or for each object
as its own copy of its methods?
The former.
I should qualify this, I suppose. The code for the class's member
functions does not affect the size of the class, because the code is
not data. However, if you define the member function inline (as you do
in your example), then if the compiler complies with your inlining
request, a new copy of that code is inserted every time you call that
member function. It still has nothing to do with the size of the
constructed object, though, and each object does not have "its own copy
of it" member functions.
Best regards,
Tom
Jon Slaughter wrote: Are methods of a class created only once for all objects or for each object
as its own copy of its methods?
Once, the instance of the object is identified by the this pointer.
It seems that I can only access an object method's address using :: so if I
have a class with method func and I want its address I would do
&someClass::som eFunc which seems to imply that there is only one function
per class(and hence for all instantiations of that class)... when I create a
very large array of objects of that class it seems to back this up as the
file size does not change much...
I just want to be sure that there is no need to deal with static members and
stuff for no to make sure I optimize size if the compiler handles it
automatically(w hich I hope it does)? i.e. there is virtually no difference
between these two classes
Note that a pointer to a member function is a different beast from a
pointer to a static member.
Ian
"Thomas Tutone" <Th***********@ yahoo.com> wrote in message
news:11******** *************@z 14g2000cwz.goog legroups.com...
Thomas Tutone wrote: Jon Slaughter wrote: > Are methods of a class created only once for all objects or for each
> object
> as its own copy of its methods?
The former.
I should qualify this, I suppose. The code for the class's member
functions does not affect the size of the class, because the code is
not data. However, if you define the member function inline (as you do
in your example), then if the compiler complies with your inlining
request, a new copy of that code is inserted every time you call that
member function. It still has nothing to do with the size of the
constructed object, though, and each object does not have "its own copy
of it" member functions.
Best regards,
Tom
Ok, as long as the compiler does its best to optimize code and data so that
there is not any wasted space then its ok. Obviously if its inline then one
would increase the code size(but this, I think, is irrespective of the
number of objects but the number of calls to the inline function?).
Just wanted to make sure that in general the number of objects created do
not increase the size proportional to the method code size(obviously it has
to do with the data). It seemed like a logical thing to do and my examples
were only giving the right outcome but i wasn't completely sure if I was
missing something since I wasn't doing a very thorough test.
Thanks,
Jon
"Ian" <ia******@hotma il.com> wrote in message
news:11******** *******@drone2-svc-skyt.qsi.net.nz ... Jon Slaughter wrote: Are methods of a class created only once for all objects or for each
object as its own copy of its methods?
Once, the instance of the object is identified by the this pointer.
It seems that I can only access an object method's address using :: so if
I have a class with method func and I want its address I would do
&someClass::som eFunc which seems to imply that there is only one function
per class(and hence for all instantiations of that class)... when I
create a very large array of objects of that class it seems to back this
up as the file size does not change much...
I just want to be sure that there is no need to deal with static members
and stuff for no to make sure I optimize size if the compiler handles it
automatically(w hich I hope it does)? i.e. there is virtually no
difference between these two classes
Note that a pointer to a member function is a different beast from a
pointer to a static member.
how so? I thought static functions were identical to global functions as
far as the internal representation was concerned? If there is only one
function, wether static or not, per class then what is the difference?
Ian
Thanks,
Jon
Jon Slaughter wrote: "Ian" <ia******@hotma il.com> wrote in message Note that a pointer to a member function is a different beast from a
pointer to a static member.
how so? I thought static functions were identical to global functions as
far as the internal representation was concerned?
That's true.
If there is only one
function, wether static or not, per class then what is the difference?
I think Ian means that they involve two different kinds of _pointers_.
Take a look at Section 33 of the FAQ to see the difference: http://www.parashift.com/c++-faq-lit...o-members.html
Best regards,
Tom
"Thomas Tutone" <Th***********@ yahoo.com> wrote in message
news:11******** **************@ g44g2000cwa.goo glegroups.com.. .
Jon Slaughter wrote: "Ian" <ia******@hotma il.com> wrote in message > Note that a pointer to a member function is a different beast from a
> pointer to a static member.
>
how so? I thought static functions were identical to global functions as
far as the internal representation was concerned?
That's true.
If there is only one
function, wether static or not, per class then what is the difference?
I think Ian means that they involve two different kinds of _pointers_.
Take a look at Section 33 of the FAQ to see the difference:
http://www.parashift.com/c++-faq-lit...o-members.html
You mean the
a.. Its type is "int (*)(char,float) " if an ordinary function
b.. Its type is "int (Fred::*)(char, float)" if a non-static member
function of class Fred
part?
Seems to me that this only addresses the resolution of the function but
internally they are the same? (just pointers) Its up to the compiler to
determine how those pointers function and there arguments to be placed on
the stack properly, etc...
I mean, as far as I can see its just saying that if I wanted to create a
pointer to a member function I have to use that syntax so the compiler will
"know" but in all actuality its still just a pointer function that the
resolution is just some "meta syntax" that exists in the language to make it
easier to program and keep things encapsulated(i. e. I could write everytin
in C that would produce the "exact" same code that doesn't use classes or
anything but the classes are really just a way to group data and code to
make programming easier but ultimately it pretty much represents the same
machine code in the long run?)?
Best regards,
Tom
Jon
"Thomas Tutone" <Th***********@ yahoo.com> wrote in message
news:11******** **************@ g44g2000cwa.goo glegroups.com.. .
Jon Slaughter wrote: "Ian" <ia******@hotma il.com> wrote in message > Note that a pointer to a member function is a different beast from a
> pointer to a static member.
>
how so? I thought static functions were identical to global functions as
far as the internal representation was concerned?
That's true.
If there is only one
function, wether static or not, per class then what is the difference?
I think Ian means that they involve two different kinds of _pointers_.
Take a look at Section 33 of the FAQ to see the difference:
http://www.parashift.com/c++-faq-lit...o-members.html
You mean the
a.. Its type is "int (*)(char,float) " if an ordinary function
b.. Its type is "int (Fred::*)(char, float)" if a non-static member
function of class Fred
part?
Seems to me that this only addresses the resolution of the function but
internally they are the same? (just pointers) Its up to the compiler to
determine how those pointers function and there arguments to be placed on
the stack properly, etc...
I mean, as far as I can see its just saying that if I wanted to create a
pointer to a member function I have to use that syntax so the compiler will
"know" but in all actuality its still just a pointer function that the
resolution is just some "meta syntax" that exists in the language to make it
easier to program and keep things encapsulated(i. e. I could write everytin
in C that would produce the "exact" same code that doesn't use classes or
anything but the classes are really just a way to group data and code to
make programming easier but ultimately it pretty much represents the same
machine code in the long run?)?
Best regards,
Tom
Jon
Jon Slaughter wrote:
You mean the
a.. Its type is "int (*)(char,float) " if an ordinary function
b.. Its type is "int (Fred::*)(char, float)" if a non-static member
function of class Fred
part?
Seems to me that this only addresses the resolution of the function but
internally they are the same? (just pointers) Its up to the compiler to
determine how those pointers function and there arguments to be placed on
the stack properly, etc...
No, they are not. That's what I was trying to say before.
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-------------------------------------------------------------
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