Re: Class with functions that return STL containers with incomplete types

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Wed, 9 Jan 2008 14:33:59 -0500

Message-ID:

<fm37j9$646$1@news.datemas.de>

Christopher wrote:

On Jan 9, 12:12 pm, massysett <OriginalOm...@gmail.com> wrote:

Greetings,

Having classes with member objects that have STL containers of
objects whose definitions are incomplete results in undefined
behavior. See for example:

http://www.ddj.com/database/184403814#8http://www.parashift.com/c++-faq-lite/misc-technical-issues.html#faq-...

I am wondering: is it okay to have member functions that return an
STL container with an incomplete type? My member objects do not
contain incomplete types. For instance, would the following code be
OK? Thanks. --Omari

#include <boost/shared_ptr.hpp>
#include <vector>

class HasSelf
{
public:
    HasSelf(std::vector<HasSelf>& contents);
    std::vector<HasSelf> getContents() const;

private:
    std::vector<boost::shared_ptr<HasSelf> > _contents;

};

Why in the world would you make a class that contains multiple
instances of itself instead of a class for an element and a separate
class that contains elements?

It could be the way to organize a hierarchical structure of objects.

Also, in order to create a vector of objects, those objects have to
have a default copy constuctor, which the HasSelf class does not
have.

That's not necessary. The objects have to be Copy-Constructible
and Assignable. Only if you create the vector using the default
constructor without the prototype object, the object needs to be
Default-Constructible.

V
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