C++ 类作为其他类的成员，如何定义它？

Question

为属于另一个类的成员的类编写定义(给定代码，不要问我为什么)。无论如何，我得到一个类型“类”重定义错误，因为我不熟悉 C++、对象的嵌套和限定符“::”

这里是 stack.h

    // rest of code above         
    public: // prototypes to be used by the client

   /**  UnderFlow Class
   *    thrown if a pop or top operation would cause the stack to underflow
   */
    class OverFlow
    {
        public:
            /*! @function   OverFlow Constructor
            *   @abstract   constructs the overflow object
            *   @param      string the error message of the overflow exception
            */
            OverFlow(std::string);

            /*! @function   getMessage
            *   @abstract   returns the message containing this exception's error text
            *   @result     string the error message of the overflow exception
            */
            std::string getMessage();

        private:
            std::string message;//error text

    };

    /** UnderFlow Class
    *   thrown if a pop or top operation would cause the stack to underflow
    */
    class UnderFlow
    {
        public:
            /*! @function   UnderFlow Constructor
            *   @abstract   constructs the underflow object
            *   @param      string the error message of the underflow exception
            */
            UnderFlow(std::string);

            /*! @function   getMessage
            *   @abstract   returns the message containing this exception's error text
            *   @result     string the error message of the underflow exception
            */
            std::string getMessage();
    //rest of code below

这里是 stack.cpp

    //rest of code above
    class stack::OverFlow
    {

string message;
OverFlow::OverFlow()
{

}

OverFlow(string errormessage)
{
    OverFlow::message = errormessage;
}

string OverFlow::getMessage()
{
    return message;
}

};
   class stack::UnderFlow
    {
string message;

UnderFlow::UnderFlow()
{

}

UnderFlow::UnderFlow(string errormessage)
{
    message = errormessage;
}

string UnderFlow::getMessage()
{
    return message;
}


};//rest of code below

我在以下代码行中遇到重定义错误

class stack::UnderFlow
class stack::OverFlow

我确信这是一个简单的修复，我只是缺乏实践...

Answer 1

类定义应该出现在头文件中，而不是 C++ 文件中。删除:

class stack::OverFlow
{

来自 C++ 文件。