获取一个类中的字段数 [英] get the number of fields in a class

问题描述

是否可以获取类的字段数？

Is there a way to get the number of fields of a class?

struct Base {
    char a;
    int b;
};

struct Derived : Base {
    std::string c;
};

static_assert(num_fields<Base>::value == 2);
static_assert(num_fields<Derived>::value == 1);

我发现这个问题，但是它已经过时了-我希望可以将某些东西与C ++ 14/17结合在一起（毕竟我们现在有了类似 magic_get -也许是其中的一个子集...？）

I've found this question but it is very dated - I am hoping something can be stitched together with C++14/17 (after all we now have something like magic_get - perhaps some subset from it...?)

编辑：-即使仅适用于MSVC或GCC或Clang，编译器挂钩也将起作用-我全部使用了3。

- a compiler hook would also work even if it's only for MSVC or GCC or Clang - I use all 3.

推荐答案

实际上是安东尼Polukhin向我们展示了自C ++ 14起，C ++ 确实具有（某种）反射；并且您可以提取有关字段的信息。 ...至少对于普通旧数据结构/类而言。观看他的CppCon 2016演讲：

Indeed, Antony Polukhin has shown us that C++ does have (some) reflection, since C++14, without knowing it; and that you can extract information about the fields. ... well, at least for plain-old-data structs/classes. Watch his CppCon 2016 talk:

C ++ 14思考如果没有宏，标记或外部工具/ Antony Polukhin

然后使用：

template <class T>
constexpr std::size_t fields_count() noexcept;

这可以使您获得字段计数。要使用它，您需要以下两个文件：

which gets you the field count. To use that you need these two file:

> https://github.com/apolukhin/magic_get/blob/develop/include/boost/pfr/detail/config.hpp

https://github.com/apolukhin/magic_get/ blob / develop / include / boost / pfr / detail / fields_count.hpp

，就足够了。

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