如何转发声明一个内部类？ [英] How do I forward declare an inner class?

问题描述

可能重复：

C ++中嵌套类型/类的向前声明

我有一个类像这样...

I have a class like so...

class Container {
public:
    class Iterator {
        ...
    };

    ...
};

在其他地方，我想通过引用传递一个Container :: Iterator，但我不想包括头文件。如果我试图转发声明类，我得到编译错误。

Elsewhere, I want to pass a Container::Iterator by reference, but I don't want to include the header file. If I try to forward declare the class, I get compile errors.

class Container::Iterator;

class Foo {
    void Read(Container::Iterator& it);
};

编译上述代码给出...

Compiling the above code gives...

test.h:3: error: ‘Iterator’ in class ‘Container’ does not name a type
test.h:5: error: variable or field ‘Foo’ declared void
test.h:5: error: incomplete type ‘Container’ used in nested name specifier
test.h:5: error: ‘it’ was not declared in this scope

我如何转发声明这个类，所以我不必包括声明Iterator类的头文件？ p>

How can I forward declare this class so I don't have to include the header file that declares the Iterator class?

推荐答案

这根本不可能。您不能向容器外部声明一个嵌套结构。您只能转发在容器中声明它。

This is simply not possible. You cannot forward declare a nested structure outside the container. You can only forward declare it within the container.

您需要执行以下操作之一

You'll need to do one of the following

• 非嵌套


• 更改声明顺序，以便嵌套类首先完全定义


• 创建一个公共基类，函数并由嵌套类实现。

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