Re: iterating over fields

James Kanze <>
Tue, 16 Nov 2010 03:25:05 -0800 (PST)
On Nov 15, 7:10 pm, Andrea Crotti <> wrote:

Supposing I have a class with many objects which are also of class

I've been wondering for a long time how I can iterate over them, and
maybe I found a solution:

    auto_ptr<Serializable> fields[NUM_FIELDS];

and then during initialization do

    fields[0] = auto_ptr<Serializable>(&currentLocation);
    fields[1] = auto_ptr<Serializable>(&address);

It's very suspicious to take the address of something in the
constructor of an auto_ptr. It can be legal, if e.g. you have:

    Serializable& currentLocation = *new Serializable;

But that's a very unusual idiom.

and supposing they all have the method "check" I could do

for (int i = 0; i < NUM_FIELDS; ++i)
    if (! (fields[i]->check()))
       return false;

return true;

for example, which looks quite nice.
Does it make sense?

I don't know. First, I'd like to know why
std::vector<Serializable> doesn't work. Or if polymorphism is
required, std::vector<std::shared_ptr<Serializable> >, or better
yet, a wrapper vector_ptr which takes care of the memory
management and the extra layer of indirection.

Maybe I should give completely to auto_ptr the control?

In what way?

And also I tried first with a vector but it doesn't work,

Why not?

I read on the internet something but I really didn't get why

vector<auto_ptr<Serializable> > is not digested by C++...

You cannot have a vector of auto_ptr, because auto_ptr isnt
CopyConstructable, in the sense required by vector. Other smart
pointers are, or if you really want a vector of polymorphic
objects owned by the vector, say boost::ptr_vector (a much
better solution).

James Kanze

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