class object initialisation

[A]

Hi,

I have always been taught to use an inialization list for initialising data
members of a class. I realize that initialsizing primitives and pointers use
an inialization list is exactly the same as an assignment, but for class
types it has a different effect - it calls the copy constructor.

My question is when to not use an initalisation list for initialising data
members of a class?
Regards
Adi

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[Attila Feher]

Alexander Terekhov wrote:

Attila Feher wrote:

Alexander Terekhov wrote:

White Wolf wrote:
I can copy it around. (at lest I hope so).

Nope. You can't copy it AS POINTER. std::vector<unsigned char> will
work, though. ;-)

Not even as void?

void pointer? It will also not work. You'll hit undefined
behavior as soon as you try to 'use' deleted/freed pointer
as pointer...

But that was the *whole* point: I do *not* want to use it as a pointer. I
never want to dereference it or apply arithmetics to it.

--
Attila aka WW

[Attila Feher]

tom_usenet wrote:

Nope. You can't copy it AS POINTER. std::vector<unsigned char> will
work, though. ;-)

Not even as void?

This is illegal, even though it isn't dereferenced:

void* p = ::operator new(1);

operator delete(p);

void* q = p; // boom

You aren't allowed to convert a pointer to an rvalue after deleting
it. You can of course reassign it:
p = 0; //or whatever.

Ahha. Makes sense, but quite restrictive. So basically you will need to
store it as "whatever", but not as a pointer if you want to keep the value
around.

--
Attila aka WW

[Alexander Terekhov]

Attila Feher wrote:
[...]

Ahha. Makes sense, but quite restrictive. So basically you will need to
store it as "whatever", but not as a pointer if you want to keep the value
around.

Even if you store it BEFORE free-ing... since the representation
may have quite a few garbage bits, storing it as "whatever" will
be nothing but "absolutely pointless exercise"... well, just a
few exceptions (I have a patent appl on one of those ;-) ) aside,
of course.

regards,
alexander.

[jeffc]

"Gary Labowitz" <gl*******@comcast.net> wrote in message
news:sj********************@comcast.com...

"jeffc" <no****@nowhere.com> wrote in message
news:3f********@news1.prserv.net...

Check what you wrote 2 posts ago. You're going around in circles.

It's called a loop.

Just trying to give the guy a break.
(get it?)

[Attila Feher]

Alexander Terekhov wrote:

Attila Feher wrote:
[...]

Ahha. Makes sense, but quite restrictive. So basically you will
need to store it as "whatever", but not as a pointer if you want to
keep the value around.

Even if you store it BEFORE free-ing... since the representation
may have quite a few garbage bits, storing it as "whatever" will
be nothing but "absolutely pointless exercise"... well, just a
few exceptions (I have a patent appl on one of those ;-) ) aside,
of course.

Since looking at them later is a "platform dependent exercise" I believe
that whatever garbage bits they have it does not really matter at all.

class DeadPtr {
unsigned char bitz[sizeof(void*)]; // Could be char *
public:
DeadPtr( void const* p) { memcpy and so on}
DeadPtr( void const* const p) { memcpy and so on}
// Something special/platform dependent to display it
};

Off course ;-) this thingy has to be made _before_ the delete is being
called. I dunno if passing as reference counts as use as rvalue... if not
that can be done.

--
Attila aka WW

[White Wolf]

Gary Labowitz wrote:
[SNIP]

Well, I like your obfuscation! I didn't understand anything! It's
ready for publication!
On the serious side, the fact that there are invalid combinations of
bits for types introduces a whole new complexity for me, and makes
the standard almost unbearably complex. Oh well, reality must be
faced.
On the whole, I rather prefer Java: nine simple types to learn about,
all well defined with regard to bit usage and size, no surprises.

Nine types? No surprises? I dunno, but whenever I had to try to find
something in the Java libraries (find+understand) I finally gave up. It is
like having to talk to all Chineese and Indian people to find a street
address. Messy.

Anyways. C++ is a general purpose programming language with systems
programming in mind. Comparing it to Java is like comparing apples to the
moon.

--
WW aka Attila

[White Wolf]

Gary Labowitz wrote:

Thank you. If this be the case, then all my musings are incorrect.
Hmm... check sum bits in a value. Yes, it could. Then invalid bit
combinations could exist. All resulting in undefined behavior I
should think.
Yep. In fact of life it is quite unusual for the "common people" to find a
HW which works like this. Anyways using a garbage value is not a really
good thing to do, even if one can get away with it without a crash.
Back to the drawing board!!!
[Gee, what did we go back to before they invented drawing boards?]

Me go bangbang wife. :-) Or maybe: back to the cave wall. :-)

--
WW aka Attila