关于c ++：实现虚函数时对vtable的未定义引用

Undefined reference to vtable while implementing virtual functions

本问题已经有最佳答案，请猛点这里访问。

我尝试用杰西自由和Tim Keogh来实现"C++编程入门"的例子，但是实现纯虚拟函数是编译而不是构建。它给出了错误：未定义对"vtable for circle"的引用

我试过用变量itsRadius代替虚拟函数GetItsRadius，看它是否能工作，但它开始给我在switch语句中的错误，但Rectangle和Square的错误是一样的，而且和以前的circle的错误也是一样的。

代码如下：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123

#include <iostream>

using namespace std;

enum BOOL { FALSE, TRUE };

class Shape
{
public:
Shape(){}
~Shape(){}
virtual long GetArea() = 0; // error
virtual long GetPerim()= 0;
virtual void Draw() = 0;
private:
};

void Shape::Draw()
{
cout <<"Abstract drawing mechanism!
";
}

class Circle : public Shape
{
public:
Circle(int radius):itsRadius(radius){}
~Circle(){}
long GetArea() { return 3 * itsRadius * itsRadius; }
long GetPerim() { return 9 * itsRadius; }
void Draw();
private:
int itsRadius;
int itsCircumference;
};

class Rectangle : public Shape
{
public:
Rectangle(int len, int width):
itsLength(len), itsWidth(width){}
~Rectangle(){}
long GetArea() { return itsLength * itsWidth; }
long GetPerim() { return 2*itsLength + 2*itsWidth; }
virtual int GetLength() { itsLength; }
virtual int GetWidth() { itsWidth; }
void Draw();
private:
int itsWidth;
int itsLength;
};

void Rectangle::Draw()
{
for (int i = 0; i<itsLength; i++)
{
for (int j = 0; j<itsWidth; j++)
cout <<"x";

cout <<"
";
}
Shape::Draw();
}

class Square : public Rectangle
{
public:
Square(int len);
Square(int len, int width);
~Square(){}
long GetPerim() {return 4 * GetLength();}
};

Square::Square(int len):
Rectangle(len,len)
{}

Square::Square(int len, int width):
Rectangle(len,width)
{
if (GetLength() != GetWidth())
cout <<"Error, not a square... a Rectangle??
";
}

void startof()
{
int choice;
BOOL fQuit = FALSE;
Shape * sp;

while (1)
{
cout <<"(1)Circle (2)Rectangle (3)Square (0)Quit:
";
cin >> choice;

switch (choice)
{
case 1: sp = new Circle(5);
break;
case 2: sp = new Rectangle(4,6);
break;
case 3: sp = new Square (5);
break;
default: fQuit = TRUE;
break;
}
if (fQuit)
break;

sp->Draw();
cout <<"
";
}
}

int main()
{
startof();
}