例如使用shared_ptr的？ [英] Example to use shared_ptr?
问题描述
您好我今天问了一个问题关于<一个href=\"http://stackoverflow.com/questions/3475030/different-types-of-objects-in-the-same-vector-array\">How插入不同类型的对象在同一载体阵列并在这个问题我的code是
Hi I asked a question today about How to insert different types of objects in the same vector array and my code in that question was
gate* G[1000];
G[0] = new ANDgate() ;
G[1] = new ORgate;
//gate is a class inherited by ANDgate and ORgate classes
class gate
{
.....
......
virtual void Run()
{ //A virtual function
}
};
class ANDgate :public gate
{.....
.......
void Run()
{
//AND version of Run
}
};
class ORgate :public gate
{.....
.......
void Run()
{
//OR version of Run
}
};
//Running the simulator using overloading concept
for(...;...;..)
{
G[i]->Run() ; //will run perfectly the right Run for the right Gate type
}
和我想用这样的载体有人写了我应该做的：
and I wanted to use vectors so someone wrote that I should do that :
std::vector<gate*> G;
G.push_back(new ANDgate);
G.push_back(new ORgate);
for(unsigned i=0;i<G.size();++i)
{
G[i]->Run();
}
但随后他和其他许多人建议我会更好地使用升压指针容器结果
或的shared_ptr 。我花了近3小时来阅读这个话题，但文档似乎pretty提前给我。 **谁能给我的shared_ptr 使用小code的例子，为什么他们建议使用的shared_ptr 。也有其他类型，如 ptr_vector ， ptr_list 和 ptr_deque **
but then he and many others suggested that I would better use Boost pointer containers
or shared_ptr. I have spent the last 3 hours reading about this topic, but the documentation seems pretty advanced to me . **Can anyone give me a small code example of shared_ptr usage and why they suggested using shared_ptr. Also are there other types like ptr_vector, ptr_list and ptr_deque **
EDIT1：我读了code例子太多，其中包括：
I have read a code example too that included:
typedef boost::shared_ptr<Foo> FooPtr;
.......
int main()
{
std::vector<FooPtr> foo_vector;
........
FooPtr foo_ptr( new Foo( 2 ) );
foo_vector.push_back( foo_ptr );
...........
}
和我不明白的语法！
推荐答案
使用的shared_ptr 的矢量删除内存泄漏是因为你忘了走路的载体，并调用删除每个元素的可能性。让我们通过例子行由行略加修改的版本。
Using a vector of shared_ptr removes the possibility of leaking memory because you forgot to walk the vector and call delete on each element. Let's walk through a slightly modified version of the example line-by-line.
typedef boost::shared_ptr<gate> gate_ptr;
创建共享指针类型的别名。这就避免了从分型结果C ++语言的丑陋的std ::矢量＆lt;提高:: shared_ptr的＆LT;门＆GT; ＆GT; 和遗忘之间的空间闭幕的大于号的
Create an alias for the shared pointer type. This avoids the ugliness in the C++ language that results from typing std::vector<boost::shared_ptr<gate> > and forgetting the space between the closing greater-than signs.
std::vector<gate_ptr> vec;
创建的空载体的boost :: shared_ptr的＆LT;门方式＆gt; 对象
gate_ptr ptr(new ANDgate);
分配一个新的 ANDgate 实例，并将其存储到的shared_ptr 。的原因，用于分别操作这是prevent如果操作抛出可能发生的问题。这是不可能在这个例子。该升压的shared_ptr 最佳实践解释为什么它是一个的最佳实践的分配到一个独立的对象，而不是一个临时的。
Allocate a new ANDgate instance and store it into a shared_ptr. The reason for doing this separately is to prevent a problem that can occur if an operation throws. This isn't possible in this example. The Boost shared_ptr "Best Practices" explain why it is a best practice to allocate into a free-standing object instead of a temporary.
vec.push_back(ptr);
这会在载体和复印件 PTR 进入一个新的共享指针。在的shared_ptr 的胆量的引用计数确保了 PTR 被安全地转移到载体内部分配的对象。
This creates a new shared pointer in the vector and copies ptr into it. The reference counting in the guts of shared_ptr ensures that the allocated object inside of ptr is safely transferred into the vector.
什么是没有解释的是，析构函数的shared_ptr＆LT;门＆GT; 确保分配的内存被删除。这是避免了内存泄漏的地方。为 STD析构函数::矢量＆lt; T＆GT; 确保了 T 调用析构函数存储在每一个元素向量。然而，析构函数指针（例如，门* ）的不会删除你已分配的内存。这是你要设法避免使用什么的shared_ptr 或 ptr_vector 。
What is not explained is that the destructor for shared_ptr<gate> ensures that the allocated memory is deleted. This is where the memory leak is avoided. The destructor for std::vector<T> ensures that the destructor for T is called for every element stored in the vector. However, the destructor for a pointer (e.g., gate*) does not delete the memory that you had allocated. That is what you are trying to avoid by using shared_ptr or ptr_vector.
这篇关于例如使用shared_ptr的？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
