C++ STL：带指针的列表 - 迭代器无法访问？
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C++ STL: list with Pointers - Iterator cannot access?
提问by Stefan
I am struggeling with an STL list that holds Pointers of my "Object" object.
我正在努力处理一个包含我的“对象”对象指针的 STL 列表。
I declared:
我声明：
list<Object*> objectlist;
and inserted via:
并通过以下方式插入：
this->objectlist.push_back(new Object(address,value,profit));
and tried to iterate like in maps and others:
并尝试像在地图和其他人中一样进行迭代：
list<Object*>::iterator iter;
iter = this->objectlist.begin();
while(iter != this->objectlist.end())
{
iter->print();
}
Where print() is a public Method of class Object;
其中 print() 是类 Object 的公共方法；
Whats wrong here?
这里有什么问题？
I cannot access via iterator to the objects in the list ?
我无法通过迭代器访问列表中的对象？
回答by RC.
You need (*iter)->print();
你需要 (*iter)->print();
Since you have an iterator to a pointer, you have to first de-reference the iterator (which gets you the Object*) then the arrow de-references the Object *and allows the call to print.
由于您有一个指向指针的迭代器，因此您必须首先取消引用迭代器（它为您提供Object*），然后箭头取消引用Object *并允许调用打印。
回答by Kerrek SB
You are not incrementing your iterator! Change your whileloop to a forloop like so:
你没有增加你的迭代器！将while循环更改为如下for循环：
for (list<Object*>::const_iterator iter = this->objectlist.begin(),
end = this->objectlist.end();
iter != end;
++iter)
{
(*iter)->print();
}
(Also iterdereferencesto a pointer, like the other answers have pointed out.)
（也iter取消对指针的引用，就像其他答案指出的那样。）
回答by Juho
You can access the value pointed by iterator with *iter
您可以使用 *iter 访问迭代器指向的值
Also, remember to increment the iterator in each iteration. Otherwise you get stuck in an endless loop.
另外，请记住在每次迭代中递增迭代器。否则你会陷入无限循环。
Like this:
像这样：
iter = this->objectlist.begin();
while(iter != this->objectlist.end())
{
(*iter)->print();
iter++;
}
回答by alanw
You could try the C++11 way (if possible). The dereference of the iterator comes free :)
您可以尝试 C++11 方式（如果可能）。迭代器的取消引用是免费的:)
for (auto& iter: this->objectlist)
{
iter->print();
}
Also if print() is a const function you should use
此外，如果 print() 是一个 const 函数，您应该使用
for (const auto& iter: this->objectlist)
回答by ollo
Instead of the for-loop you should use STL's for_each()- see the advantages of for_eachover a simple for-loop.
for您应该使用 STL而不是-loop for_each()- 查看for_each相对于简单for-loop的优势。
Syntax
句法
#include <algorithm> // 'for_each()' is in there
std::for_each(InputIterator first, // Iterator start position
InputIterator last, // Iterator end position
Function fn); // Unary function - executed on all elements in range
for_eachexample
for_each例子
Here's how your example looks std::for_each()instead of for( ... ):
这是您的示例的外观std::for_each()而不是for( ... )：
list<Object*> objectlist;
// insert some elements …
// Deletes all elements of 'objectlist'
std::for_each(objectlist.begin(), objectlist.end(), DeleteObj<Object*>());
Unary function
一元函数
The unary function is implemented using a template, so you can use it with anytype. Just make sure Tis a pointer type!
一元函数是使用模板实现的，因此您可以将它用于任何类型。只要确保T是指针类型！
template<class T> class DeleteObj
{
public:
bool operator()(T obj) const
{
delete obj;
return true;
}
};
Btw. you don't haveto implement this as template. And: you can binda member function instead of such a implementation too!
顺便提一句。您不必将此实现为模板。并且：您也可以绑定成员函数而不是这样的实现！
Documentation
文档
回答by Frerich Raabe
An iterator references an element in the list, so for a list of type T, dereferencing an iterator yields a value of type T.
迭代器引用列表中的一个元素，因此对于 type 的列表T，取消引用迭代器会产生一个 type 的值T。
In your case, Tis actually a pointer - Object*. Hence, the iter->call (which dereferences the iterator) yields a pointer. You have to dereference that pointer to get to the actuala object.
在您的情况下，T实际上是一个指针 - Object*。因此，iter->调用（取消对迭代器的引用）产生一个指针。您必须取消引用该指针才能到达实际对象。
Try using
尝试使用
(*iter)->print()
instead.
反而。
回答by u804609
you should use the following way:
您应该使用以下方式：
(*iter)->print()
