std :: variant和boost :: variant之间有什么区别？

本文介绍了std :: variant和boost :: variant之间有什么区别？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 29岁程序员，3月因学历无情被辞！ 在此问题的答案中： C ++标准库中的boost :: variant等效于什么？ 有人提到 boost :: variant 和 std :: variant 有所不同。 就使用这些类的人而言，有什么区别？ 有什么动机委员会是否表示采用具有这些差异的 std :: variant ？ 使用这两个代码进行编码时应注意什么？ ，以保持与切换到另一个的最大兼容性？ （动机是使用 boost :: variant 在C ++ 17之前的代码中）解决方案 分配/安置行为： boost :: variant 可能在执行赋值时将其分配给实时的变量。有 a控制何时发生的规则数量，因此 boost :: variant 是否分配内存取决于 Ts 实例化。 std :: variant 将从不动态分配内存。但是，作为对C ++对象复杂规则的让步，如果抛出分配/放置，则变体 可以进入 valueless_by_exception状态。在这种状态下，不能访问变体，也不能访问用于访问特定成员作品的任何其他功能。 只有在分配/安置抛出时，您才能进入此状态。 升压。变体包括 recursive_variant ，其中允许变体包含自身。实际上，它们是指向 boost :: variant 的指针的特殊包装，但它们与访问机制绑定在一起。 std :: variant 没有此类帮助程序类型。 std :: variant 提供了更多使用C ++ 11后功能的功能。例如： 它将转发特殊成员的 noexcept 状态 它具有基于可变参数模板的就地构造函数和放置功能。 缺陷解决方案应用于C ++ 17可能意味着它还将转发其类型的普通可复制性。也就是说，如果所有类型都是微不足道的，那么 variant< Ts> 也是如此。 In an answer to this SO question:What is the equivalent of boost::variant in the C++ standard library?it is mentioned that boost::variant and std::variant differ somewhat.What are the differences, as far as someone using these classes is concerned?What motivation did the committee express to adopt std::variant with these differences?What should I watch out for when coding with either of these, to maintain maximum compatibility with switching to the other one?(the motivation is using boost::variant in pre-C++17 code) 解决方案Assignment/emplacement behavior:boost::variant may allocate memory when performing assignment into a live variant. There are a number of rules that govern when this can happen, so whether a boost::variant will allocate memory depends on the Ts it is instantiated with.std::variant will never dynamically allocate memory. However, as a concession to the complex rules of C++ objects, if an assignment/emplacement throws, then the variant may enter the "valueless_by_exception" state. In this state, the variant cannot be visited, nor will any of the other functions for accessing a specific member work.You can only enter this state if assignment/emplacement throws.Boost.Variant includes recursive_variant, which allows a variant to contain itself. They're essentially special wrappers around a pointer to a boost::variant, but they are tied into the visitation machinery.std::variant has no such helper type.std::variant offers more use of post-C++11 features. For example:It forwards the noexcept status of the special member functions of its constituent types.It has variadic template-based in-place constructors and emplacement functions.Defect resolutions applied to C++17 may mean that it will also forward trivial copyability of its types. That is, if all of the types are trivially copyable, then so too will variant<Ts>. 这篇关于std :: variant和boost :: variant之间有什么区别？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！ 上岸，阿里云！