源文件中的嵌套类定义 [英] Nested Class Definition in source file

问题描述

首先，如果此问题已被问过，我们深表歉意。我搜索了一会儿，但没有找到答案，很可能是因为我不知道如何正确地打字。

如果我有一个类似的嵌套类：

  class MyClass 
 {
 class NestedClass 
 {
 public：
 //嵌套类成员和这里的定义
}; 
 
 //主类成员这里
}; 
  

目前， MyClass 的定义 CPP 文件，但是 NestedClass 的定义在头文件中，也就是说，我不能声明函数/在 CPP 文件中。

所以我的问题是，如何在cpp文件中定义 NestedClass 的函数？如果我不能，原因是什么（如果是这样，我有一个模糊的想法，为什么会发生，但我想要一个很好的解释）？结构怎么样？

解决方案

如果你的内部类有如下方法：

  class MyClass {
 class NestedClass 
 {
 public：
 void someMethod（）; 
}; 
 
 //主类成员这里
}; 
  

...那么你可以在.cpp文件中定义它，如下：

  void MyClass :: NestedClass :: someMethod（）{
 // blah 
} 
  

结构与C ++中的类几乎相同 - 只是默认为public。

您可以（如注释中所述）只是声明一个内部类，例如：

/ p>

  class MyClass {
 class NestedClass; 
 // blah 
}; 
  

..然后在实施文件中定义：

  class MyClass :: NestedClass {
 // etc. 
}; 
  

First off, I apologize if this question has been asked before. I searched for a while but did not find the answer, most likely because I don't know how to word it properly. Onto the question.

If I have a nested class like so:

  class MyClass
  {
    class NestedClass
    {
    public:
      // nested class members AND definitions here
    };

    // main class members here
  };

Currently, the definitions of MyClass are in the CPP file but the definitions for NestedClass are in the header file, that is, I cannot declare the functions/constructors in the CPP file.

So my question is, how do I define the functions of NestedClass in the cpp file? If I cannot, what is the reason (and if this is the case, I have a vague idea of why this happens but I would like a good explanation)? What about structures?

解决方案

You can. If your inner class has a method like:

  class MyClass   {
    class NestedClass
    {
    public:
      void someMethod();
    };

    // main class members here
  };

...then you can define it in the .cpp file like so:

void MyClass::NestedClass::someMethod() {
   // blah
}

Structures are almost the same thing as classes in C++ — just defaulting to 'public' for their access. They are treated in all other respects just like classes.

You can (as noted in comments) just declare an inner class, e.g.:

class MyClass   {
    class NestedClass;
    // blah
};

..and then define it in the implementation file:

class MyClass::NestedClass {
  // etc.
};

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