文刀旋子

List_deconstructor

28 May 2014

如果用容器存副本，则容器销毁的时候，副本也会自动被删除。

如果用容器存指针，则容器销毁的时候，不会删除这些指针所指向的对象，因此必须先手工删除完毕之后，再销毁容器。

list<Foo*> foo_list;

###Method 1

static bool deleteAll( Foo * theElement ) { delete theElement; return true; }
foo_list . remove_if ( deleteAll );

###Method 2

template< typename T >
struct delete_ptr : public std::unary_function<bool,T>
{
   bool operator()(T*pT) const { delete pT; return true; }
};

std::for_each( foo_list.begin(), foo_list.end(), delete_ptr<Foo>() );

###Method 3

for(list<Foo*>::const_iterator it = foo_list.begin(); it != foo_list.end(); it++)
{
	delete *it;
} 
foo_list.clear();

for(auto &it:foo_list) delete it; foo_list.clear();  #c++11

###Method 4

while(!foo.empty()) delete foo.front(), foo.pop_front();  #std::list
template<typename Container>
void delete_them(Container& c) 
{ 
	while(!c.empty()) delete c.back(), c.pop_back();
}

while(!bar.empty()) delete bar.back(), bar.pop_back();    #std::vector

###Method 5

At least for a list, iterating and deleting, then calling clear at the end is a bit inneficient since it involves traversing the list twice, when you really only have to do it once.

Here is a little better way:

for (list<Foo*>::iterator i = foo_list.begin(), e = foo_list.end(); i != e; )
{
	list<Foo*>::iterator tmp(i++);
	delete *tmp;
	foo_list.erase(tmp);
}

###MORE 0

template <typename T>
class Deleter {
public:
  Deleter(T* pointer) : pointer_(pointer) { }
  Deleter(const Deleter& deleter) {
	Deleter* d = const_cast<Deleter*>(&deleter);
	pointer_ = d->pointer_;
	d->pointer_ = 0;
  }
  ~Deleter() { delete pointer_; }
  T* pointer_;
};

Example

std::list<Deleter<Foo> > foo_list;
foo_list.push_back(new Foo());
foo_list.clear();

###MORE 1

The request was to “safely clean up” the container. But the safety of that code relies on several methods not throwing exceptions: begin(), end(), iterator::operator!=, iterator::operator*, iterator::operator++. Surpirsingly, such reliance is unsafe

One of the pitfalls is that, perversely, the STL allows several important iterator operations to throw exceptions. This makes many “obvious” approaches using iteration through a container unsafe.

(boost pointer container library)[http://www.boost.org/doc/libs/1_37_0/libs/ptr_container/doc/ptr_container.html]

###MORE2

Actually, I believe the STD library provides a direct method of managing memory in the form of the allocator class

You can extend the basic allocator’s deallocate() method to automatically delete the members of any container.

I /think/ this is the type of thing it’s intended for.

Reference Here