Re: Problem with initialization of array of class objects
* James Kanze:
On Feb 21, 3:49 pm, "Alf P. Steinbach" <al...@start.no> wrote:
* yatko:
I want to define an array of objects and initialize them,
but I don't know how I could do that simply. I have searched
over net, and have found a few solutions. Does anybody has a
better, simple solution?
Suppose there is a Foo class that has const member.
class Foo
{
public:
Foo(int, int);
~Foo();
private:
const int ID;
double int var;
};
First method:
Foo objects [MAX] = {Foo(0,1),Foo(1,2),Foo(2,3)};
This method works nicely.
For his class above, yes. As he later indicates, he was holding
out on us---his actual class contains a boost::mutex, which
isn't copiable.
// This one requires copy constructor, but I have const members, so it
doesn't work for me.
It's opposite: the method below requires copy constructor,
while the one above doesn't.
No. They both require the copy constructor. To begin with,
aggregate initialization is copy initialization.
You're right, I didn't know that. It's not very logical and MSVC 7.1
handles lack of copy constructor fine (which is logical, it's not
technically needed except when initializer is an object of a derived
class, only formally, and only a very obnoxious compiler would actually
do that unnecessary copying!). Though now that you mentioned it, I
checked and g++ detects the formal problem, and Comeau does, and I found
it hidden away in ?12.6.1/2 and also ?8.5/12.
Have you any idea why on earth that rule is there, what problem it's
meant to help us avoid? I can understand that it helps with the
standard-writer's internal problem of specifying the notation, the
special case of derived class object as initializer. But, it's
completely in breach of the "don't pay for what you're not using"
principle of C++, and the C++0x fix of 'T const&' argument semantics.
So, it looks like a defect to me: if I want that array of
non-copy-constructible objects, the compiler should let me have it
(without resorting to placement new), as MSVC does...
[snip]
I want to initialize the array as following, but it doesn't work.
Foo objects[MAX] = {{0,1},{1,2},{2,3}};
Works OK.
Huh?
Sorry. I didn't see that it was different. Again you're right.
Cheers,
- Alf
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?