使用#include和Inclusion防护措施在单独文件中进行C ++继承 [英] C++ Inheritance in Separate Files Using #include and Inclusion Guards

问题描述

我是Stack Overflow的新手，正在教自己C ++，但仍然是个初学者.在完成了我正在使用的一本书的大部分内容(可能被认为过时和/或不是一本好书)之后，我决定通过自己尝试一些概念来加强一些概念，仅在需要时才引用该书，但是我似乎被卡住了.我要解决的概念是继承，多态性，抽象数据类型(ADT)，并将类的代码分为头文件(.h)和C ++文件(.cpp).抱歉，我只想清楚和明确我要去的地方.

I am new to Stack Overflow and am teaching myself C++, but am still quite a beginner. After completing a nice chunk of the book I am using (which may be considered out dated and/or not a great book) I decided to re-enforce some concepts by trying them on my own, referencing the book only if needed, but I appear to be stuck. The concepts I am trying to tackle are inheritance, polymorphism, abstract data types (ADT), and separating the code for my classes into header files (.h) and C++ file (.cpp). Sorry in advance for the wall of text, I just want to be clear and specific where I need to be.

因此，我的目标是创建简单的形状类，并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myPoly的概念，则myPoly应该是ADT，因为其中一种方法是纯虚函数(区域方法)，因为创建myPoly对象不是我想要的用户. myRectangle和myTriangle都从myPoly派生，而mySquare又从myRectangle派生.我还计划在测试班级时加入我的测试程序.我在使用Code :: Blocks 10.05并在构建test.cpp程序时不断出现以下错误:

So, my goal is to create simple shape classes that inherit from one another where applicable. I have four classes: myPoly, myRectangle, myTriangle, and mySquare. myPoly, if I understood this concept correctly, should be an ADT since one of the methods is a pure virtual function (area method), since creating a myPoly object isn't something I would want a user of my classes to do. myRectangle and myTriangle both derive from myPoly and in turn mySquare derives from myRectangle. I've also included my test program where I planned on testing my classes. I am using Code::Blocks 10.05 and keep getting the following error when I build my test.cpp program:

undefined reference to 'myPoly::myPoly()'

对于myPoly类的方法，我都遇到了42个类似的错误.当我尝试为myRectangle和myTriangle生成.cpp文件时，也会发生这种情况.通过研究，我试图解决这个小项目遇到的问题，我觉得我的包含卫士或我的#include语句有问题，并且没有正确包含或包含过多次.最初，我是将myPoly的.cpp文件提供给myRectangle和myTriangle，但在几个地方读到，包括myPoly的.h文件会更有效，以及如何自动将其.cpp包括在内.如果有人能对此提供一些见识，将不胜感激.我还记得有关在包含声明中使用引号与在尖括号中使用引号的不同之处.以下是我为我的小项目制作的所有九个文件.大部分评论只是给我的小笔记或提醒.

I get 42 similar errors all for the methods of the myPoly class. This happens when I try to build the .cpp files for myRectangle and myTriangle too. With the research I tried to do on the problems I been running into with this little project I feel like something is wrong with my inclusion guards or my #include statements, and something isn't getting included properly or is getting included too many times. At first I was providing the .cpp file for myPoly to myRectangle and myTriangle, but read in a couple of places that including the .h file for myPoly is more efficient and some how automatically include its .cpp. If anyone can provide some insight on that, it would be greatly appreciated. I also remember something about how using quotes in your inclusion statements is different than using the angle brackets. Below are all nine files that I have made for my little project. Most of the comments are little notes or reminders to me.

//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()
{
}

test.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收到这些错误，或者为什么我所做的某些事情可能不被认为是好的/最佳实践，而不是仅仅收到一行代码来使我的错误消失.

I am very curious as to why I am getting these errors or why something I did may not be considered good/best practice, as opposed to just receiving a line of code to make my errors go away.

推荐答案

您的包含防护措施看起来不错.如果不是，则很可能会出现编译器错误，包括文件和行号信息.您发布的错误似乎更像是链接器错误.

Your inclusion guards look fine. If they were not, you would most likely get a compiler error, including file and line number information. The error you posted seems more like a linker error.

但是，您的代码存在一个问题".通常，您应该仅#include .h文件，而不是.cpp文件.

However, there is one "problem" with your code. As a general rule, you should only #include .h files and not .cpp files.

现在进入解决方案:我不熟悉Code :: Blocks self.但是，我希望我能提供一些一般信息，这些信息将为您指明正确的方向.默认情况下，我过去使用的一些编译器允许我编译一个C ++文件并运行该程序.要编译一个带有多个文件的程序，我必须创建一个项目. (大多数现代编译器会迫使您从头开始创建一个项目.)考虑到这一点，我建议您检查一下如何在Code :: Blocks中为您的程序创建一个项目.

Now to get to the solution: I am unfamiliar with Code::Blocks myself. However, I hope I can give some general information that will point you in the right direction. Some compilers I have used in the past by default allowed me to compile a single C++ file and run the program. To compile a program with more than one file, I had to create a project. (Most modern compilers force you to create a project from the start.) With this in mind, I would suggest you check out how to create a project for your program in Code::Blocks.

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