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Guest
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 Posted: Fri Sep 15, 2006 1:45 am Post subject: User-defined iterator |
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Object A is composed of a vector of A (itself) and a vector of B. I'm
running into difficulties creating an iterator of all the Bs (those
contained within the vector of As as well as the vector of Bs.)
Somehow I have to maintain the state within the iterator of which A and
which B of that A I'm on, but this seems to break the recursive nature
of "A is composed of As."
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Jens Theisen
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| Posted: Fri Sep 15, 2006 4:58 am Post subject: Re: User-defined iterator |
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jddahl (AT) gmail (DOT) com writes:
| Quote: | Object A is composed of a vector of A (itself) and a vector of B. I'm
running into difficulties creating an iterator of all the Bs (those
contained within the vector of As as well as the vector of Bs.)
Somehow I have to maintain the state within the iterator of which A and
which B of that A I'm on, but this seems to break the recursive nature
of "A is composed of As."
|
So you want to do a recursive traversal through this structure as in
struct B { };
struct A
{
std::vector< A > m_a;
std::vector< B > m_b;
};
void traverse(A const& a)
{
for(size_t i = 0; i < m_a.size(); ++i)
{
traverse(a.m_a[i]);
}
for(size_t i = 0; i < m_b.size(); ++i)
{
do_stuff(a.m_b[i]);
}
}
Is that correct?
Can you be a bit more precise on the problem?
If you want to make a proper iterators that's a bit more difficult and
you probably want to avoid that if you just want to get a particular
problem sovled.
Also note that the definition of A is invalid since A is incomplete in
the instantiation of vector< A >, but that's not a problem in
practice - no STL will actually complain.
Best regards,
Jens
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Carlos Moreno
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| Posted: Fri Sep 15, 2006 4:59 am Post subject: Re: User-defined iterator |
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jddahl (AT) gmail (DOT) com wrote:
| Quote: | Object A is composed of a vector of A (itself) and a vector of B. I'm
running into difficulties creating an iterator of all the Bs
|
You should be running into difficulties creating the above. STL
containers require complete types, even the requirement does not
always translate into a "material limitation".
In other words, maybe, depending on how loose the compiler is,
you might get away with creating a class A that has a data member
vector<A>, since the *physical contents* (the data) of the
vector<A> is, at most, pointers to A, and so no infinite
recursion is created.
But the thing is, vector *requires* a complete type, and a
compliant compiler has the right to (and should?) enforce
such requirement.
Am I misunderstanding something?
Carlos
--
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Thomas Tutone
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| Posted: Fri Sep 15, 2006 4:59 am Post subject: Re: User-defined iterator |
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jddahl (AT) gmail (DOT) com wrote:
| Quote: | Object A is composed of a vector of A (itself) and a vector of B.
|
Can you give an example? At first glance, this sounds impossible.
What you are describing is something like this:
struct A {
std::vector<A> vec_a;
std::vector<B> vec_b;
};
That's not possible, because A is an incomplete type for purposes of
the vector declaration, which should cause a compile error. Perhaps
you meant Object A is composed of a vector of (preferably smart)
pointers to A and a vector of Bs?
| Quote: | I'm
running into difficulties creating an iterator of all the Bs (those
contained within the vector of As as well as the vector of Bs.)
Somehow I have to maintain the state within the iterator of which A and
which B of that A I'm on, but this seems to break the recursive nature
of "A is composed of As."
|
A recursive algorithm can we rewritten iteratively, although it may be
substantially more complex. Presumably the iterator could push a
pointer to each A it encountered onto a stack or other suitable
container, to ensure you traversed every A of the object. But your
iterator will not be lightweight if it has to maintain such a
structure.
Best regards,
Tom
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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