c++ - Unresolved external symbol 链接器错误(C++)

我正在尝试为我的项目之一开发抽象设计模式代码，如下所示。.但是，我无法编译该代码..给了一些编译错误(如“ Unresolved external symbol ” public:virtual void __thiscall Xsecs::draw_lines (double，double)“(？draw_lines @ Xsecs @@ UAEXNN @ Z)”)。任何人都可以帮我这个忙...

#include "stdafx.h"
#include <iostream>
#include <vector>
#include "Xsecs.h"
using namespace std;
//Product class

class Xsecs
{
public:
    virtual void draw_lines(double pt1, double pt2);
    virtual void draw_curves(double pt1, double rad);
};

class polyline: public Xsecs
{
public:
    virtual void draw_lines(double pt1,double pt2)
    {
        cout<<"draw_line in polygon"<<endl;
    }
     virtual void draw_curves(double pt1, double rad)
    {
        cout<<"Draw_curve in circle"<<endl;
    }
    /*void create_polygons()
    {
        cout<<"create_polygon_thru_draw_lines"<<endl;
    }*/
};

class circle: public Xsecs
{
 public:
     virtual void draw_lines(double pt1,double pt2)
    {
        cout<<"draw_line in polygon"<<endl;
    }
     virtual void draw_curves(double pt1, double rad)
    {
        cout<<"Draw_curve in circle"<<endl;
    }
    /*void create_circles()
    {
        cout<<"Create circle"<<endl;
    }*/
};

//Factory class
class Factory
{
public:
 virtual polyline* create_polyline()=0;
 virtual circle* create_circle()=0;
};

class Factory1: public Factory
{
public:
      polyline* create_polyline()
{
    return new polyline();
}
      circle* create_circle()
{
    return new circle();
}
};

class Factory2: public Factory
{
public:
      circle* create_circle()
{
    return new circle();
}
     polyline* create_polyline()
{
    return new polyline();
}
};

int _tmain(int argc, _TCHAR* argv[])
{
    Factory1 f1;
    Factory * fp=&f1;
    return 0;
}

最佳答案

我想您正在尝试创建虚拟基类。您需要在Xsecs类的draw_lines和draw_curves方法的末尾添加“= 0”

class Xsecs
{
public:
    virtual void draw_lines(double pt1, double pt2) = 0;
    virtual void draw_curves(double pt1, double rad) = 0;
};

编译器在提示，因为您还没有任何相关方法的实现。