...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Boost.Intrusive also offers associative containers that can be very useful when creating more complex associative containers, like containers maintaining one or more indices with different sorting semantics. Boost.Intrusive associative containers, like most STL associative container implementations are based on red-black trees.
The memory overhead of these containers is usually 3 pointers and a bit (with alignment issues, this means 3 pointers and an integer). This size can be reduced to 3 pointers if pointers have even alignment (which is usually true in most systems).
An empty, non constant-time size set
,
multiset
or rbtree
has also the size of 3 pointers
and an integer (3 pointers when optimized for size). These containers have
logarithmic complexity in many operations like searches, insertions, erasures,
etc. set
and multiset
are the intrusive equivalents
of standard std::set
and std::multiset
containers.
rbtree
is a superset
of set
and multiset
containers that offers functions to insert unique and multiple keys.
set
, multiset
and rbtree
share the
same hooks. This is an advantage, because the same user type can be inserted
first in a multiset
and after that in set
without changing the definition of the user class.
template <class ...Options> class set_base_hook;
set_base_hook
:
the user class derives publicly from set_base_hook
to make it set
/multiset
-compatible.
template <class ...Options> class set_member_hook;
set_member_hook
:
the user class contains a public set_member_hook
to make it set
/multiset
-compatible.
set_base_hook
and set_member_hook
receive the same options explained in the section How
to use Boost.Intrusive plus a size optimization option:
tag<class Tag>
(for base hooks only): This argument serves as a tag, so you can derive
from more than one base hook. Default: tag<default_tag>
.
link_mode<link_mode_type
LinkMode>
:
The linking policy. Default: link_mode<safe_link>
.
void_pointer<class VoidPointer>
:
The pointer type to be used internally in the hook and propagated to the
container. Default: void_pointer<void*>
.
optimize_size<bool Enable>
:
The hook will be optimized for size instead of speed. The hook will embed
the color bit of the red-black tree node in the parent pointer if pointer
alignment is even. In some platforms, optimizing the size might reduce
speed performance a bit since masking operations will be needed to access
parent pointer and color attributes, in other platforms this option improves
performance due to improved memory locality. Default: optimize_size<false>
.
template <class T, class ...Options> class set; template <class T, class ...Options> class multiset; template <class T, class ...Options> class rbtree;
These containers receive the same options explained in the section How to use Boost.Intrusive:
base_hook<class Hook>
/ member_hook<class T, class
Hook,
Hook T::* PtrToMember>
/ value_traits<class ValueTraits>
: To specify the hook type
or value traits used to configure the container. (To learn about value
traits go to the section Containers
with custom ValueTraits.)
constant_time_size<bool Enabled>
:
To activate the constant-time size()
operation. Default: constant_time_size<true>
size_type<bool Enabled>
:
To specify the type that will be used to store the size of the container.
Default: size_type<std::size_t>
And they also can receive an additional option:
compare<class Compare>
:
Comparison function for the objects to be inserted in containers. The comparison
functor must induce a strict weak ordering. Default: compare< std::less<T> >
Now let's see a small example using both hooks and both containers:
#include <boost/intrusive/set.hpp> #include <vector> #include <algorithm> #include <cassert> using namespace boost::intrusive; //This is a base hook optimized for size class MyClass : public set_base_hook<optimize_size<true> > { int int_; public: //This is a member hook set_member_hook<> member_hook_; MyClass(int i) : int_(i) {} friend bool operator< (const MyClass &a, const MyClass &b) { return a.int_ < b.int_; } friend bool operator> (const MyClass &a, const MyClass &b) { return a.int_ > b.int_; } friend bool operator== (const MyClass &a, const MyClass &b) { return a.int_ < b.int_; } }; //Define a set using the base hook that will store values in reverse order typedef set< MyClass, compare<std::greater<MyClass> > > BaseSet; //Define an multiset using the member hook typedef member_hook<MyClass, set_member_hook<>, &MyClass::member_hook_> MemberOption; typedef multiset< MyClass, MemberOption> MemberMultiset; int main() { typedef std::vector<MyClass>::iterator VectIt; typedef std::vector<MyClass>::reverse_iterator VectRit; //Create several MyClass objects, each one with a different value std::vector<MyClass> values; for(int i = 0; i < 100; ++i) values.push_back(MyClass(i)); BaseSet baseset; MemberMultiset membermultiset; //Check that size optimization is activated in the base hook assert(sizeof(set_base_hook<optimize_size<true> >) == 3*sizeof(void*)); //Check that size optimization is deactivated in the member hook assert(sizeof(set_member_hook<>) > 3*sizeof(void*)); //Now insert them in the reverse order in the base hook set for(VectIt it(values.begin()), itend(values.end()); it != itend; ++it){ baseset.insert(*it); membermultiset.insert(*it); } //Now test sets { BaseSet::reverse_iterator rbit(baseset.rbegin()), rbitend(baseset.rend()); MemberMultiset::iterator mit(membermultiset.begin()), mitend(membermultiset.end()); VectIt it(values.begin()), itend(values.end()); //Test the objects inserted in the base hook set for(; it != itend; ++it, ++rbit) if(&*rbit != &*it) return 1; //Test the objects inserted in the member hook set for(it = values.begin(); it != itend; ++it, ++mit) if(&*mit != &*it) return 1; } return 0; }