C++ 源文件中的嵌套类定义
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Nested Class Definition in source file
提问by Samaursa
If I have a nested class like so:
如果我有一个像这样的嵌套类：
class MyClass
{
class NestedClass
{
public:
// nested class members AND definitions here
};
// main class members here
};
Currently, the definitions of MyClassare in the CPPfile but the definitions for NestedClassare in the header file, that is, I cannot declare the functions/constructors in the CPPfile.
目前， 的定义MyClass在CPP文件中，而 的定义NestedClass在头文件中，也就是说，我不能在CPP文件中声明函数/构造函数。
So my question is, how do I define the functions of NestedClassin 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?
所以我的问题是，如何定义NestedClasscpp 文件中的函数？如果我不能，原因是什么（如果是这种情况，我对为什么会发生这种情况有一个模糊的想法，但我想要一个很好的解释）？结构呢？
回答by sje397
You can. If your inner class has a method like:
你可以。如果你的内部类有一个类似的方法：
class MyClass {
class NestedClass
{
public:
void someMethod();
};
// main class members here
};
...then you can define it in the .cpp file like so:
...然后您可以在 .cpp 文件中定义它，如下所示：
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.
结构与 C++ 中的类几乎相同——只是默认为“公共”以供访问。他们在所有其他方面都像类一样被对待。
You can(as noted in comments) just declare an inner class, e.g.:
您可以（如评论中所述）只声明一个内部类，例如：
class MyClass {
class NestedClass;
// blah
};
..and then define it in the implementation file:
..然后在实现文件中定义它：
class MyClass::NestedClass {
// etc.
};
