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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[Ivan Vecerina]

"A" <[e-mail]. au> wrote in message
news:3f******** @news.iprimus.c om.au...
| 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?

Only when you are unable to, e.g. when a complex computation involving
several intermediate variables is needed and a dedicated function doesn't
make sense.

IMO the initialization list should always be preferred.
Regards,
--
http://ivan.vecerina.com

[jeffc]

"A" <[e-mail]. au> wrote in message
news:3f******** @news.iprimus.c om.au...

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?

The basic rule of thumb is that anything that can go in the initialize list
should go there. Obviously, you can't put something like this in there:
if (a)
i = 2;
else
i = 4;

[Erik]

> > 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?

The basic rule of thumb is that anything that can go in the initialize

list should go there. Obviously, you can't put something like this in there:
if (a)
i = 2;
else
i = 4;

Many, if not most, of those cases can be covered by the ?: operator:
MyClass(int a) : i(a ? 2 : 4) {}

/ Erik

[Gianni Mariani]

Erik wrote:
....

should go there. Obviously, you can't put something like this in there:
if (a)
i = 2;
else
i = 4;

Many, if not most, of those cases can be covered by the ?: operator:
MyClass(int a) : i(a ? 2 : 4) {}

Yep - and sometimes it makes sense to create a function that does more
complex things so that everything is in the initializer list.

[jeffc]

"Gianni Mariani" <gi*******@mari ani.ws> wrote in message
news:bj******** @dispatch.conce ntric.net...

Erik wrote:
...

should go there. Obviously, you can't put something like this in there:
if (a)
i = 2;
else
i = 4;

Many, if not most, of those cases can be covered by the ?: operator:
MyClass(int a) : i(a ? 2 : 4) {}

Yep - and sometimes it makes sense to create a function that does more
complex things so that everything is in the initializer list.

And how exactly do you propose calling such a function from the initializer
list?

[jeffc]

"Erik" <[e-mail]> wrote in message news:bj******** **@news.lth.se. ..

The basic rule of thumb is that anything that can go in the initialize

list

should go there. Obviously, you can't put something like this in there:
if (a)
i = 2;
else
i = 4;

Many, if not most, of those cases can be covered by the ?: operator:
MyClass(int a) : i(a ? 2 : 4) {}

Yeah, maybe simple "if" cases like that, but you can't put logic or function
calls (other than base class constructors) in the initializer list. You
added an expression, not a statement.

[Ron Natalie]

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

Yep - and sometimes it makes sense to create a function that does more
complex things so that everything is in the initializer list.

And how exactly do you propose calling such a function from the initializer
list?

Same way you call any other function. It behooves you not to use the
yet uninitialized parts of the object being constructed though.

[Ron Natalie]

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

Many, if not most, of those cases can be covered by the ?: operator:
MyClass(int a) : i(a ? 2 : 4) {}

Yeah, maybe simple "if" cases like that, but you can't put logic or function
calls (other than base class constructors) in the initializer list. You
added an expression, not a statement.

Who says you can't have function calls?

[Kevin Goodsell]

Ying Yang wrote:

Never.
Initializatio n lists are the only way to *initialize* members of a class
or to specify which constructor from a base class should be used.

No, it's not the only way - as i mentioned you can use an assignment
operator for initialising primitive data members, which is the same as using
an initialization list.

No, you cannot initialize anything with an assignment operator ever.
Assignment operators assign, they don't initialize. If you don't the
difference, you should look it up.

-Kevin
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