Re: Using a STL container of type self in a class declaration
On 6 Nov., 16:29, ros...@gmail.com wrote:
I have a question that I hope is appropriate for this group -
Is the following code compliant to the standard
#include <list>
class B
{
std::list<B> b_list;
};
The reason I ask is because this compiles with gcc and visual studio,
but not with borland c++. I also find it a difficult question to just
look up in the standard, so hopefully somebody can help me out.
The standard says that the behavior of your code is undefined.
We can draw this conclusion by combining [lib.res.on.functions]/2
"In particular, the effects are undefined in the following cases:
[..]
? if an incomplete type (3.9) is used as a template argument when
instantiating a template component."
and [class.mem]/2:
"A class is considered a completely-defined object type (3.9) (or
complete type) at the closing } of the class-specifier. Within the
class member-specification, the class is regarded as complete within
function bodies, default arguments and constructor ctor-initializers
(including such things in nested classes). Otherwise it is regarded
as incomplete within its own class member-specification."
Your example uses a class B which has a (non-static) data member
std::list<B>. At the point, where b_list is declared, B is still
incomplete.
std::list is a standard library component, which is the relevant
context for the first quote, which only applies to templates of
the standard library.
As a workaround I suggest that you use std::list<B*> or
std::list<boost::shared_ptr<B> >.
HTH & Greetings from Bremen,
Daniel Kr?gler
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