问题描述
是否有任何方法可以获取std::any存储的数据大小(以字节为单位)?我想出的唯一解决方法是通过std::any::type查询其值的类型，然后将结果与已知类型的列表(例如my_any.type() == typeid(T))进行比较，然后将大小设置为sizeof(T).不幸的是，这种解决方案仅在事先知道类型的情况下才有效.
Is there any way to get the size (in bytes) of the data stored by std::any? The only workaround I came up with is querying the type of its value by std::any::type and comparing the result to a list of known types like my_any.type() == typeid(T), then the size is sizeof(T). Unfortunately, this solution only works when the types are known beforehand.
你知道什么解决办法吗?
Do you know any solution?
推荐答案
您无法获取std::any持有的对象的大小(您提到的解决方法除外). std::any是类型擦除的 minimum 实现.
You cannot get the size of the object held by std::any (other than the workaround you've mentioned). std::any is a minimal implementation of type erasure.
如果您想要更强大的功能，请自己编写(这并不难，只需在std::any或boost::any上建模并添加size()功能).您可能还需要添加许多其他内容，例如I/O，将多个数据(或任何容器的内容)存储为数组等.
If you want something more powerful, write it yourself (it's not hard, just model it on std::any or boost::any and add the size() functionality).There are many other things you may want to add to any, such as I/O, storing multiple data (or the contents of any container) as arrays, etc..
如Vittorio的.
At the expense of an additional data member (to store the size), you may also extend std::any by writing a wrapper, as suggested in Vittorio's answer.
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