无法从另一个名称空间创建类的实例? [英] Cannot create an instance of a class from another namespace?

问题描述

好的，这真的很麻烦.我从未遇到过这样的事情.

Okay, so this is really werid. I've never encountered anything like this.

我的程序的一部分(无法编译)包含以下三个名称空间:

Part of my program (Fails to compile) contains three namespaces as following:

// namespaceA.h
namespace A {
enum Kind { jimmy, david };
}
// end of namespaceA.h

// namespaceB.h
#include "namespaceA.h"
namespace B {
class Tree {
    public:
    Tree *prev;
    Tree *next;
    Tree *down;
    A::Kind kind;

    Tree();
    ~Tree();
};
}
// end of namespaceB.h
// Implementation details of the class are placed in namespaceB.cc
// Constructor / Desctructor defined in the namespaceB.cc file!
// Something like this,
#include "namespaceB.h"
namespace B {
inline Tree::Tree() { ... }
inline Tree::~Tree() { ... }
}

// namespaceC.cc
#include "namespace.B"
namespace C {
void run() {
    B::Tree *tree;    // FINE
    B::Tree tree;     // Fail to compile!?
}
}
// end of namespaceC.cc

现在，g ++运行得很好，但是链接器ld抱怨:

Now, g++ went along just fine but the linker ld complains:

 "namespaceC.cc: undefined reference to `B::Tree::Tree()'
 "namespaceC.cc: undefined reference to `B::Tree::~Tree()'

我以前从未遇到过这样的事情……这看起来真的很奇怪，我什至不知道任何单词/术语来描述这个问题.

I have never ever encountered anything like this before... This just seems really weird, I don't even know any words/terms to describe this problem.

非常感谢您的帮助.

谢谢

推荐答案

您对B::Tree::Tree()和B::Tree::~Tree()的定义是内联声明的.这意味着它们仅在该源文件中可用，而在其他任何文件中均不可用.

Your definitions of B::Tree::Tree() and B::Tree::~Tree() are declared inline. This means they are only available in that source file, not any others.

从定义中删除inline，或者将内联定义移动到需要它们的所有源文件所包含的头文件中，都应该解决链接错误.

Either removing inline from the definitions, or moving the inline definitions into a header file included by all source files that need them, should fix the link errors.

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