我怎么会用的for_each删除一个STL地图的每一个值? [英] How would I use for_each to delete every value in an STL map?
问题描述
假设我有一个STL地图,该值是三分球,我想将它们全部删除。我将如何重新present以下code,但利用的std :: for_each的呢?我很高兴的解决方案,使用升压。
的(stdext ::的hash_map< INT,符*> ::迭代器IR = myMap.begin();
IR = myMap.end()!;
++ IR)
{
删除的IR>第二个; //删除所有(富*)值。
}
(我发现Boost的 checked_delete
,但我不知道如何应用到对< INT,符*>
迭代器重新presents)。
(另外,对于这个问题的目的,忽视的事实是存储需要删除的STL容器原始指针不是非常明智的)。
注意:我后来发现,下面列出一个单行的答案......但是code是pretty的可怕,所以我已经接受GMAN的理智的答案 。 P>
您必须做出一个函数对象:
结构second_deleter
{
模板< typename的T>
void运算符()(const的T&安培; PX)常量
{
删除pX.second;
}
};
的std :: for_each的(myMap.begin(),myMap.end(),second_deleter());
如果您使用的是刺激,你也可以使用λ文库:
命名空间BL =提高::拉姆达;
的std :: for_each的(myMap.begin(),myMap.end(),second_deleter()
BL ::绑定(BL :: delete_ptr()
BL ::绑定(STD :: select2nd< MYMAP :: value_type的>(),_1));
但你可以尝试指针容器库,做到这一点自动。
请注意您不使用地图,但的hash_map
。我建议你切换至升压的 unordered_map
,这是更大的电流。然而,似乎没有成为一个 ptr_unordered_map
。
为了安全起见,你应该换这个东西了。例如:
模板< typename的T,类型名的删除>
结构wrapped_container
{
的typedef牛逼CONTAINER_TYPE;
类型定义删除器deleter_type;
wrapped_container(const的T&安培; pContainer):
集装箱(pContainer)
{}
〜wrapped_container(无效)
{
的std :: for_each的(container.begin(),container.end(),deleter_type());
}
牛逼的容器;
};
和使用它像:
的typedef wrapped_container<
提高:: unordered_map< INT,符*>中second_deleter> my_container;
my_container.container ./* ... * /
这确保了无论什么时候,您的容器将通过一个删除器迭代。 (对于例外,例如。)
比较:
的std ::矢量<为int *>伏;
v.push_back(新INT);
抛出漏!; //没有在矢量被删除
wrapped_container<的std ::矢量<为int *> >伏;
v.container.push_back(新INT);
抛出无泄漏!; // wrapped_container自毁,删除元素
Suppose I have a STL map where the values are pointers, and I want to delete them all. How would I represent the following code, but making use of std::for_each? I'm happy for solutions to use Boost.
for( stdext::hash_map<int, Foo *>::iterator ir = myMap.begin();
ir != myMap.end();
++ir )
{
delete ir->second; // delete all the (Foo *) values.
}
(I've found Boost's checked_delete
, but I'm not sure how to apply that to the pair<int, Foo *>
that the iterator represents).
(Also, for the purposes of this question, ignore the fact that storing raw pointers that need deleting in an STL container isn't very sensible).
Note: I have subsequently found and listed a one-line answer below... but the code is pretty awful so I've accepted GMan's saner answer.
You have to make a function object:
struct second_deleter
{
template <typename T>
void operator()(const T& pX) const
{
delete pX.second;
}
};
std::for_each(myMap.begin(), myMap.end(), second_deleter());
If you're using boost, you could also use the lambda library:
namespace bl = boost::lambda;
std::for_each(myMap.begin(), myMap.end(), second_deleter(),
bl::bind(bl::delete_ptr(),
bl::bind(std::select2nd<myMap::value_type>(), _1));
But you might try the pointer containers library which does this automatically.
Note you are not using a map, but a hash_map
. I recommend you switch to boost's unordered_map
, which is more current. However, there doesn't seem to be a ptr_unordered_map
.
For safety, you should wrap this thing up. For example:
template <typename T, typename Deleter>
struct wrapped_container
{
typedef T container_type;
typedef Deleter deleter_type;
wrapped_container(const T& pContainer) :
container(pContainer)
{}
~wrapped_container(void)
{
std::for_each(container.begin(), container.end(), deleter_type());
}
T container;
};
And use it like:
typedef wrapped_container<
boost::unordered_map<int, Foo*>, second_deleter> my_container;
my_container.container./* ... */
This ensures no matter what, your container will be iterated through with a deleter. (For exceptions, for example.)
Compare:
std::vector<int*> v;
v.push_back(new int);
throw "leaks!"; // nothing in vector is deleted
wrapped_container<std::vector<int*> > v;
v.container.push_back(new int);
throw "no leaks!"; // wrapped_container destructs, deletes elements
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