...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Some examples are given here and in the accompanying test files:
my_container.push_back( 0 ); // throws bad_ptr my_container.replace( an_iterator, 0 ); // throws bad_ptr my_container.insert( an_iterator, 0 ); // throws bad_ptr std::auto_ptr<T> p( 0 ); my_container.push_back( p ); // throws bad_ptr
ptr_vector<X> pvec; std::vector<X*> vec; *vec.begin() = new X; // fine, memory leak *pvec.begin() = new X; // compile time error ( *vec.begin() )->foo(); // call X::foo(), a bit clumsy pvec.begin()->foo(); // no indirection needed *vec.front() = X(); // overwrite first element pvec.front() = X(); // no indirection needed
ptr_vector<T> vec1; ... ptr_vector<T> vec2( vec1.clone() ); // deep copy objects of 'vec1' and use them to construct 'vec2', could be very expensive vec2 = vec1.release(); // give up ownership of pointers in 'vec1' and pass the ownership to 'vec2', rather cheap vec2.release(); // give up ownership; the objects will be deallocated if not assigned to another container vec1 = vec2; // deep copy objects of 'vec2' and assign them to 'vec1', could be very expensive ptr_vector<T> vec3( vec1 ); // deep copy objects of 'vec1', could be very expensive
// a class that has no normal copy semantics class X : boost::noncopyable { public: X* clone() const; ... }; // this will be found by the library by argument dependent lookup (ADL) X* new_clone( const X& x ) { return x.clone(); } // we can now use the interface that requires cloneability ptr_vector<X> vec1, vec2; ... vec2 = vec1.clone(); // 'clone()' requires cloning <g> vec2.insert( vec2.end(), vec1.begin(), vec1.end() ); // inserting always means inserting clones
class X { ... }; // assume 'X' is Cloneable X x; // and 'X' can be stack-allocated ptr_list<X> list; list.push_back( new_clone( x ) ); // insert a clone list.push_back( new X ); // always give the pointer directly to the container to avoid leaks list.push_back( &x ); // don't do this!!! std::auto_ptr<X> p( new X ); list.push_back( p ); // give up ownership BOOST_ASSERT( p.get() == 0 );
ptr_deque<T> deq; typedef ptr_deque<T>::auto_type auto_type; // ... fill the container somehow auto_type ptr = deq.pop_back(); // remove back element from container and give up ownership auto_type ptr2 = deq.release( deq.begin() + 2 ); // use an iterator to determine the element to release ptr = deq.pop_front(); // supported for 'ptr_list' and 'ptr_deque' deq.push_back( ptr.release() ); // give ownership back to the container
ptr_list<X> list; ptr_vector<X> vec; ... // // note: no cloning happens in these examples // list.transfer( list.begin(), vec.begin(), vec ); // make the first element of 'vec' the first element of 'list' vec.transfer( vec.end(), list.begin(), list.end(), list ); // put all the lists element into the vector
We can also transfer objects from ptr_container<Derived> to ptr_container<Base> without any problems.
incomplete_type_test.cpp: | |
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Shows how to implement the Composite pattern. | |
simple_test.cpp: | |
Shows how the usage of pointer container compares with a container of smart pointers | |
view_example.cpp: | |
Shows how to use a pointer container as a view into other container | |
tree_test.cpp: | Shows how to make a tree-structure |
array_test.cpp: | Shows how to make an n-ary tree |
This example shows many of the most common features at work. The example provide lots of comments. The source code can also be found here.
// // Boost.Pointer Container // // Copyright Thorsten Ottosen 2003-2005. Use, modification and // distribution is subject to the Boost Software License, Version // 1.0. (See accompanying file LICENSE_1_0.txt or copy at // http://www.boost.org/LICENSE_1_0.txt) // // For more information, see http://www.boost.org/libs/ptr_container/ // // // This example is intended to get you started. // Notice how the smart container // // 1. takes ownership of objects // 2. transfers ownership // 3. applies indirection to iterators // 4. clones objects from other smart containers // // // First we select which container to use. // #include <boost/ptr_container/ptr_deque.hpp> // // we need these later in the example // #include <boost/assert.hpp> #include <string> #include <exception> // // Then we define a small polymorphic class // hierarchy. // class animal : boost::noncopyable { virtual std::string do_speak() const = 0; std::string name_; protected: // // Animals cannot be copied... // animal( const animal& r ) : name_( r.name_ ) { } void operator=( const animal& ); private: // // ...but due to advances in genetics, we can clone them! // virtual animal* do_clone() const = 0; public: animal( const std::string& name ) : name_(name) { } virtual ~animal() throw() { } std::string speak() const { return do_speak(); } std::string name() const { return name_; } animal* clone() const { return do_clone(); } }; // // An animal is still not Clonable. We need this last hook. // // Notice that we pass the animal by const reference // and return by pointer. // animal* new_clone( const animal& a ) { return a.clone(); } // // We do not need to define 'delete_clone()' since // since the default is to call the default 'operator delete()'. // const std::string muuuh = "Muuuh!"; const std::string oiink = "Oiiink"; class cow : public animal { virtual std::string do_speak() const { return muuuh; } virtual animal* do_clone() const { return new cow( *this ); } public: cow( const std::string& name ) : animal(name) { } }; class pig : public animal { virtual std::string do_speak() const { return oiink; } virtual animal* do_clone() const { return new pig( *this ); } public: pig( const std::string& name ) : animal(name) { } }; // // Then we, of course, need a place to put all // those animals. // class farm { // // This is where the smart containers are handy // typedef boost::ptr_deque<animal> barn_type; barn_type barn; // // An error type // struct farm_trouble : public std::exception { }; public: // // We would like to make it possible to // iterate over the animals in the farm // typedef barn_type::iterator animal_iterator; // // We also need to count the farm's size... // typedef barn_type::size_type size_type; // // And we also want to transfer an animal // safely around. The easiest way to think // about '::auto_type' is to imagine a simplified // 'std::auto_ptr<T>' ... this means you can expect // // T* operator->() // T* release() // deleting destructor // // but not more. // typedef barn_type::auto_type animal_transport; // // Create an empty farm. // farm() { } // // We need a constructor that can make a new // farm by cloning a range of animals. // farm( animal_iterator begin, animal_iterator end ) : // // Objects are always cloned before insertion // unless we explicitly add a pointer or // use 'release()'. Therefore we actually // clone all animals in the range // barn( begin, end ) { } // // ... so we need some other function too // animal_iterator begin() { return barn.begin(); } animal_iterator end() { return barn.end(); } // // Here it is quite ok to have an 'animal*' argument. // The smart container will handle all ownership // issues. // void buy_animal( animal* a ) { barn.push_back( a ); } // // The farm can also be in economical trouble and // therefore be in the need to sell animals. // animal_transport sell_animal( animal_iterator to_sell ) { if( to_sell == end() ) throw farm_trouble(); // // Here we remove the animal from the barn, // but the animal is not deleted yet...it's // up to the buyer to decide what // to do with it. // return barn.release( to_sell ); } // // How big a farm do we have? // size_type size() const { return barn.size(); } // // If things are bad, we might choose to sell all animals :-( // std::auto_ptr<barn_type> sell_farm() { return barn.release(); } // // However, if things are good, we might buy somebody // else's farm :-) // void buy_farm( std::auto_ptr<barn_type> other ) { // // This line inserts all the animals from 'other' // and is guaranteed either to succeed or to have no // effect // barn.transfer( barn.end(), // insert new animals at the end *other ); // we want to transfer all animals, // so we use the whole container as argument // // You might think you would have to do // // other.release(); // // but '*other' is empty and can go out of scope as it wants // BOOST_ASSERT( other->empty() ); } }; // class 'farm'. int main() { // // First we make a farm // farm animal_farm; BOOST_ASSERT( animal_farm.size() == 0u ); animal_farm.buy_animal( new pig("Betty") ); animal_farm.buy_animal( new pig("Benny") ); animal_farm.buy_animal( new pig("Jeltzin") ); animal_farm.buy_animal( new cow("Hanz") ); animal_farm.buy_animal( new cow("Mary") ); animal_farm.buy_animal( new cow("Frederik") ); BOOST_ASSERT( animal_farm.size() == 6u ); // // Then we make another farm...it will actually contain // a clone of the other farm. // farm new_farm( animal_farm.begin(), animal_farm.end() ); BOOST_ASSERT( new_farm.size() == 6u ); // // Is it really clones in the new farm? // BOOST_ASSERT( new_farm.begin()->name() == "Betty" ); // // Then we search for an animal, Mary (the Crown Princess of Denmark), // because we would like to buy her ... // typedef farm::animal_iterator iterator; iterator to_sell; for( iterator i = animal_farm.begin(), end = animal_farm.end(); i != end; ++i ) { if( i->name() == "Mary" ) { to_sell = i; break; } } farm::animal_transport mary = animal_farm.sell_animal( to_sell ); if( mary->speak() == muuuh ) // // Great, Mary is a cow, and she may live longer // new_farm.buy_animal( mary.release() ); else // // Then the animal would be destroyed (!) // when we go out of scope. // ; // // Now we can observe some changes to the two farms... // BOOST_ASSERT( animal_farm.size() == 5u ); BOOST_ASSERT( new_farm.size() == 7u ); // // The new farm has however underestimated how much // it cost to feed Mary and its owner is forced to sell the farm... // animal_farm.buy_farm( new_farm.sell_farm() ); BOOST_ASSERT( new_farm.size() == 0u ); BOOST_ASSERT( animal_farm.size() == 12u ); }
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Copyright: | Thorsten Ottosen 2004-2006. Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see LICENSE_1_0.txt). |
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