使用 C++11 for() 循环遍历 vector<unique_ptr<mytype>>
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Iterating through vector<unique_ptr<mytype>> using C++11 for() loops
提问by Dimitris Sfounis
I've got the following batch of code:
我有以下一批代码：
std::vector<std::unique_ptr<AVLTree_GeeksforGeeks>> AVLArray(100000);
/* Let's add some objects in the vector */
AVLTree_GeeksforGeeks *avl = new AVLTree_GeeksforGeeks();
avl->Insert[2]; avl->Insert[5]; AVL->Insert[0];
unique_ptr<AVLTree_GeeksforGeeks> unique_p(avl);
AVLArray[0] = move(unique_p);
/* we do this for a number of other trees, let's say another 9...
...
...
Now the vector has objects up until AVLTree[9] */
/* Let's try iterating through its valid, filled positions */
for(auto i : AVLTree )
{
cout << "Hey there!\n"; //This loop should print 10 "Hey there"s.
}
Ruh roh.Compilation error at the last part, in the for() loop.
呵呵呵。最后一部分的编译错误，在 for() 循环中。
\DataStructures2013_2014\main.cpp||In function 'int main()':|
\DataStructures2013_2014\main.cpp|158|error: use of deleted function 'std::unique_ptr<_Tp, _Dp>::unique_ptr(const std::unique_ptr<_Tp, _Dp>&) [with _Tp = AVLTree_GeeksforGeeks; _Dp = std::default_delete<AVLTree_GeeksforGeeks>; std::unique_ptr<_Tp, _Dp> = std::unique_ptr<AVLTree_GeeksforGeeks>]'|
e:\codeblocks\mingw\bin\..\lib\gcc\mingw32.7.1\include\c++\bits\unique_ptr.h|256|error: declared here|
||=== Build finished: 2 errors, 0 warnings (0 minutes, 0 seconds) ===|
Any ideas on what I am doing wrong?
关于我做错了什么的任何想法？
回答by Dietmar Kühl
The loop
循环
for (auto i: AVLTree) { ... }
tries to make a copy of each element of the range in AVLTree.begin()and AVLTree.end(). Of course, std::unique_ptr<T>can't be copied: there is only one std::unique_ptr<T>to each pointer. It wouldn't really copy anything but rather stealit. That would be bad.
尝试制作AVLTree.begin()和范围内的每个元素的副本AVLTree.end()。当然std::unique_ptr<T>不能复制：std::unique_ptr<T>每个指针只有一个。它不会真正复制任何东西，而是窃取它。那会很糟糕。
You want to use references instead:
您想改用引用：
for (auto& i: AVLTree) { ... }
... or, if you don't modify them
...或者，如果您不修改它们
for (auto const& i: AVLTree) { ... }
