C++ std::auto_ptr 到 std::unique_ptr
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std::auto_ptr to std::unique_ptr
提问by Martin York
With the new standard coming (and parts already available in some compilers), the new type std::unique_ptris supposed to be a replacement for std::auto_ptr.
随着新标准的到来（以及一些编译器中已经可用的部分），新类型std::unique_ptr应该是std::auto_ptr.
Does their usage exactly overlap (so I can do a global find/replace on my code (not that I would do this, but if I did)) or should I be aware of some differences that are not apparent from reading the documentation?
它们的用法是否完全重叠（所以我可以在我的代码上进行全局查找/替换（不是我会这样做，但如果我这样做了））还是我应该知道阅读文档时不明显的一些差异？
Also if it is a direct replacement, why give it a new name rather than just improve the std::auto_ptr?
此外，如果它是直接替代品，为什么要给它一个新名称而不是仅仅改进std::auto_ptr？
回答by Cubbi
You cannot do a global find/replace because you can copy an auto_ptr(with known consequences), but a unique_ptrcan only be moved. Anything that looks like
您不能进行全局查找/替换，因为您可以复制 a auto_ptr（具有已知后果），但unique_ptr只能移动 a。任何看起来像
std::auto_ptr<int> p(new int);
std::auto_ptr<int> p2 = p;
will have to become at least like this
至少必须变成这样
std::unique_ptr<int> p(new int);
std::unique_ptr<int> p2 = std::move(p);
As for other differences, unique_ptrcan handle arrays correctly (it will call delete[], while auto_ptrwill attempt to call delete.
至于其他差异，unique_ptr可以正确处理数组（它会调用delete[]，而auto_ptr会尝试调用delete.
回答by deft_code
std::auto_ptrand std::unique_ptrare incompatible in someways and a drop in replacement in others. So, no find/replace isn't good enough. However, after a find/replace working through the compile errors should fix everything except weird corner cases. Most of the compile errors will require adding a std::move.
std::auto_ptr并且std::unique_ptr在某些方面不兼容，而在其他方面则替代品下降。因此，没有查找/替换还不够好。但是，在通过编译错误进行查找/替换之后，除了奇怪的极端情况之外，应该修复所有内容。大多数编译错误都需要添加一个std::move.
- Function scope variable:
100% compatible, as long as you don't pass it by value to another function. - Return type:
not 100% compatible but 99% compatible doesn't seem wrong. - Function parameter by value:
100% compatible with one caveat,unique_ptrs must be passed through astd::movecall. This one is simple as the compiler will complain if you don't get it right. - Function parameter by reference:
100% compatible. - Class member variable:
This one is tricky.std::auto_ptrs copy semantics are evil. If the class disallows copying thenstd::unique_ptris a drop in replacement. However, if you tried to give the class reasonable copy semantics, you'll need to change thestd::auto_ptrhandling code. This is simple as the compiler will complain if you don't get it right. If you allowed copying of a class with astd::auto_ptrmember withoutany special code, then shame on you and good luck.
- 函数作用域变量：
100% 兼容，只要您不按值将其传递给另一个函数。 - 返回类型：
不是 100% 兼容但 99% 兼容似乎没有错。 - 函数参数按值：
100% 兼容一个警告，unique_ptrs 必须通过std::move调用传递。这个很简单，因为如果你做的不对，编译器会抱怨。 - 参考函数参数：
100% 兼容。 - 类成员变量：
这个很棘手。std::auto_ptrs 复制语义是邪恶的。如果该类不允许复制，则std::unique_ptr替换掉。但是，如果您尝试为类提供合理的复制语义，则需要更改std::auto_ptr处理代码。这很简单，因为如果你做的不对，编译器会抱怨。如果您允许在没有任何特殊代码的情况下复制具有std::auto_ptr成员的类，那么您会感到羞耻并祝您好运。
In summary, std::unique_ptris an unbroken std::auto_ptr. It disallows at compile time behaviors that were oftenerrors when using a std::auto_ptr. So if you used std::auto_ptrwith the care it needed, switching to std::unique_ptrshould be simple. If you relied on std::auto_ptr's odd behavior, then you need to refactor your code anyway.
综上所述，std::unique_ptr是一个不间断的std::auto_ptr。它不允许去考虑那些编译时的行为往往使用时的错误std::auto_ptr。因此，如果您std::auto_ptr小心使用它，切换到std::unique_ptr应该很简单。如果您依赖于std::auto_ptr的奇怪行为，那么无论如何您都需要重构您的代码。
回答by UncleBens
AFAIK, unique_ptris not a direct replacement. The major flaw that it fixes is the implicit transfer of ownership.
AFAIK，unique_ptr不是直接替代品。它修复的主要缺陷是所有权的隐式转移。
std::auto_ptr<int> a(new int(10)), b;
b = a; //implicitly transfers ownership
std::unique_ptr<int> a(new int(10)), b;
b = std::move(a); //ownership must be transferred explicitly
On the other hand, unique_ptrwill have completely new capabilities: they can be stored in containers.
另一方面，unique_ptr将具有全新的功能：它们可以存储在容器中。
回答by ValarDohaeris
Herb Sutter has a nice explanation on GotW #89:
Herb Sutter 对GotW #89有很好的解释：
What's the deal with auto_ptr?auto_ptr is most charitably characterized as a valiant attempt to create a unique_ptr before C++ had move semantics. auto_ptr is now deprecated, and should not be used in new code.
If you have auto_ptr in an existing code base, when you get a chance try doing a global search-and-replace of auto_ptr to unique_ptr; the vast majority of uses will work the same, and it might expose (as a compile-time error) or fix (silently) a bug or two you didn't know you had.
auto_ptr 有什么关系？auto_ptr 被最仁慈地描述为在 C++ 具有移动语义之前创建 unique_ptr 的勇敢尝试。auto_ptr 现在已弃用，不应在新代码中使用。
如果您在现有代码库中有 auto_ptr，当您有机会尝试将 auto_ptr 全局搜索并替换为 unique_ptr；绝大多数用途都一样，它可能会暴露（作为编译时错误）或修复（悄悄地）一两个您不知道的错误。
In other words, while a global search-and-replace may "break" your code temporarily, you should do it anyway: It may take some time to fix the compile errors, but will save you a lot more trouble in the long run.
换句话说，虽然全局搜索和替换可能会暂时“破坏”您的代码，但您无论如何都应该这样做：修复编译错误可能需要一些时间，但从长远来看会为您节省更多麻烦。
