我是Stack Overflow的新手，正在自学C++，但我还是个初学者。在完成了我正在使用的书的一大部分（这本书可能被认为是过时的和/或不是一本伟大的书）后，我决定通过自己尝试来重新实施一些概念，只有在需要时才参考这本书，但我似乎被卡住了。我试图解决的概念是继承、多态性、抽象数据类型（ADT），以及将类的代码分离为头文件（.h）和C++文件（.cpp）。很抱歉提前出现了文本墙，我只想明确和具体地说明我需要在哪里。

因此，我的目标是创建简单的形状类，在适用的情况下相互继承。我有四个类：myPoly、myRectangle、myTriangle和mySquare。如果我正确理解了这个概念，myPoly应该是一个ADT，因为其中一个方法是纯虚拟函数（面积方法），因为创建myPoly对象不是我希望类的用户做的事情。myRectangle和myTriangle都派生自myPoly，而mySquare又派生自myRectanger。我还包括了我的测试程序，我计划在其中测试我的课程。我正在使用代码：：Blocks 10.05，当我构建test.cpp程序时，不断出现以下错误：

undefined reference to 'myPoly::myPoly()'

对于myPoly类的方法，我得到了42个类似的错误。当我尝试为myRectangle和myTriangle构建.cpp文件时，也会发生这种情况。通过我试图对我在这个小项目中遇到的问题进行的研究，我觉得我的包容性保护或#include语句出了问题，有些内容没有被正确地包含或被包含太多次。起初，我将myPoly的.cpp文件提供给myRectangle和myTriangle，但在一些地方读到，为myPoly包含.h文件更有效，以及如何自动包含其.cpp。如果有人能对此提供一些见解，我们将不胜感激。我还记得在包含语句中使用引号与使用尖括号的区别。以下是我为我的小项目制作的全部九个文件。大多数评论都是小笔记或提醒我。

myPoly.h

//Practice with inheritance, polymorphism, and Abstract Data Types
//header file for Polygon class
#ifndef MYPOLY_H
#define MYPOLY_H
class myPoly
{
    public:
        //constructor
        //const reference pass because the values w and h don't change and reference avoid the time it takes to copy large
        //  objects by value (if there were any)
        myPoly();
        myPoly(const float & w, const float & h);
        //destructor
        virtual ~myPoly();
        //accessors
        float getWidth();
        float getHeight();
        void setWidth(const float & w);
        void setHeight(const float & h);
        virtual float area() = 0;
    private:
        float width, height;
};
#endif

myPoly.cpp

//Practice with inheritance, polymorphism, and Abstract Data Types
//implementation file for myPoly class
#include "myPoly.h"
//constructor
myPoly::myPoly()
{
    setWidth(10);
    setHeight(10);
}
myPoly::myPoly(const float & w, const float & h)
{
    setWidth(w);
    setHeight(h);
}
//destructor
myPoly::~myPoly() {}
//accessors
float myPoly::getWidth() {return width;}
float myPoly::getHeight() {return height;}
void myPoly::setHeight(const float & w) {width = w;}
void myPoly::setWidth(const float & h) {height = h;}
//pure virtual functions have no implementation
//area() is handled in the header file

myRectangle.h

//Practice with inheritance, polymorphism, and Abstract Data Types
//declaration file for myRectangle class
#ifndef MYRECTANGLE_H
#define MYRECTANGLE_H
#include "myPoly.h"
class myRectangle : public myPoly
{
    public:
        //constructor
        myRectangle();
        myRectangle(const float & w, const float & h);
        //destructor
        ~myRectangle();
        //this doesn't need to be virtual since the derived class doesn't override this method
        float area();
};
#endif

myRectangle.cpp

//Practice with inheritance, polymorphism, and Abstract Data Types
//implementaion file for the myRectangle class
//get a vauge compiler/linker error if you have virtual methods that aren't implemented (even if it ends up being just
//  a 'stub' method, aka empty, like the destructor)
#include "myRectangle.h"
myRectangle::myRectangle()
{
    setWidth(10);
    setHeight(10);
}
myRectangle::myRectangle(const float & w, const float & h)
{
    setWidth(w);
    setHeight(h);
}
myRectangle::~myRectangle()
{
}
float myRectangle::area()
{
    return getWidth() * getHeight();
}

myTriangle.h

//Practice with inheritance, polymorphism, and Abstract Data Types
//declaration file for myTriangle class
#ifndef MYTRIANGLE_H
#define MYTRIANGLE_H
#include "myPoly.h"
//imagine the triangle is a right triangle with a width and a height
//  |
//  | 
//  |  
//  |___
class myTriangle : public myPoly
{
    public:
        //constructors
        myTriangle();
        myTriangle(const float & w, const float & h);
        //destructor
        ~myTriangle();
        //since nothing derives from this class it doesn't need to be virtual and in turn neither does the destructor
        float area();
};
#endif

myTriangle.cpp

//Practice with inheritance, polymorphism, and Abstract Data Types
//implementation file for myTriangle class
#include "myTriangle.h"
myTriangle::myTriangle()
{
    setWidth(10);
    setHeight(10);
}
myTriangle::myTriangle(const float & w, const float & h)
{
    setWidth(w);
    setHeight(h);
}
myTriangle::~myTriangle()
{
}
float myTriangle::area()
{
    return getWidth() * getHeight() / 2;
}

mySquare.h

//Practice with inheritance, polymorphism, and Abstract Data Types
//declaration file for mySquare class
#ifndef MYSQUARE_H
#define MYSQUARE_H
#include "myRectangle.cpp"
class mySquare : public myRectangle
{
    public:
        //constructors
        mySquare();
        //explicity call the myRectangle constructor within this implementation to pass w as width and height
        mySquare(const float w);
        //destructor
        ~mySquare();
};
#endif

mySquare.cpp

//Practice with inheritance, polymorphism, and Abstract Data Types
//implementation file for mySquare class
#include "mySquare.h"
mySquare::mySquare()
{
    setWidth(10);
    setHeight(10);
}
mySquare::mySquare(const float w)
{
    myRectangle::myRectangle(w, w);
}
mySquare::~mySquare()
{
}

测试.cpp

//Practice with inheritance, polymorphism, and Abstract Data Types
//main class that uses my shape classes and experiments with inheritance, polymorphism, and ADTs
#include "myRectangle.cpp"
//#include "mySquare.cpp"
#include "myTriangle.cpp"
#include <iostream>
int main()
{
    myPoly * shape = new myRectangle(20,20);
    return 0;
}

我很好奇为什么我会出现这些错误，或者为什么我所做的事情可能不被认为是好的/最佳实践，而不是仅仅接收一行代码来消除我的错误。