为什么我不能在头文件中单独写入名称空间的层次结构? [英] Why I can't separately write namespace's hierarchy in the header file?

问题描述

我写了一些头文件.我想分别声明名称空间层次结构(为清楚起见)，然后声明函数和类.对我来说，它看起来像是文档中的目录.对我而言，这将非常方便:在一处看到名称空间的完整层次结构.我这样写:

I write some header file. I want separately declare the namespaces hierarchy (for clarity), and and then declare functions and classes. For me it looks as a table of contents in the document. It would be very convenient for me: to see the full hierarchy of namespaces in one place. I write this:

// Namespaces hierarchy:
namespace Bushman{
    namespace CAD_Calligraphy{}
    //...
}

// Declarations of classes and functions
class Bushman::CAD_Calligraphy::Shp_ostream{
public:
    explicit Shp_ostream(std::ostream& ost);
};

但是，MS Visual Studio对创建头文件的这种方式大喊大叫.我应该这样写:

But MS Visual Studio shouts on such way of creation of the header file. I should write so:

namespace Bushman{
    namespace CAD_Calligraphy{
        class Shp_istream{
        public:
            explicit Shp_istream(std::istream& ist);
        };
    }
}

为什么第一个变体不起作用?这是C ++或IDE的限制吗?

Why the first variant doesn't work? Is this restriction of the C++, or IDE?

P.S.我的其他问题是此处.

P.S. My additional question is here.

谢谢.

推荐答案

该限制在§9/1中:如果类头名称包含 嵌套名称说明符，类说明符应引用 先前直接在该类中声明的类，或者 嵌套名称说明符引用的名称空间[...]. 换句话说，类名的首次出现不能在 类似于Bushman::CAD_Calligraphy::Shp_ostream.

The restriction is in §9/1: "If a class-head-name contains a nested-name-specifier, the class-specifier shall refer to a class that was previously declared directly in the class or namespace to which the nested-name-specifier refers[...]". In other words, the first appearance of the class name cannot be in something like Bushman::CAD_Calligraphy::Shp_ostream.

您可以做的是在您的初始姓名中添加前向声明 层次结构的声明:

What you can do is add forward declarations in your initial declaration of the hierarchy:

// Namespaces hierarchy:
namespace Bushman{
    namespace CAD_Calligraphy{
        class Shp_ostream;
        //...
    }
    //...
}

// Declarations of classes and functions
class Bushman::CAD_Calligraphy::Shp_ostream{
public:
    explicit Shp_ostream(std::ostream& ost);
};

取决于标题的组织方式，甚至可能是 从人的角度来看更好:您的标头以 一种其中定义的索引.

Depending on how your headers are organized, this might even be better from the human point of view: your header starts with a sort of index of what is defined in it.

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