[英]Class & method inheritance in c++
So, I thought I get it, but I don't... This is my header file shapes.h
: 所以,我以为我明白了,但是我没有...这是我的头文件
shapes.h
:
#ifndef __shapes__
#define __shapes__
class Shape {
public:
double h;
double w;
virtual double area(void);
virtual void rotate(void);
};
class Rectangle : public Shape {
public:
Rectangle(double h, double w);
double area(void);
void rotate(void);
private:
double h;
double w;
};
#endif
and then I implement it in shapes.cpp
as: 然后在
shapes.cpp
其实现为:
#include "shapes.h"
#include <cmath>
#include <math.h>
/*
* Rectangle methods
*/
Rectangle::Rectangle(double height, double width) {
this->h = height;
this->w = width;
}
double Rectangle::area() {
return this->h * this->w;
}
void Rectangle::rotate() {
double temp = this->h;
this->h = this->w;
this->w = temp;
}
And in my main.cpp
I do: 在我的
main.cpp
我做了:
#include <vector>
#include "shapes.h"
using namespace std;
int main(void){
vector<Shape *> shapes;
Rectangle u(2,5);
shapes.push_back(&u);
Rectangle v(3, 4);
shapes.push_back(&v);
double area = 0;
for(Shape * p : shapes){
area += p->area();
}
...
And I get this error: 我得到这个错误:
Undefined symbols for architecture x86_64:
"typeinfo for Shape", referenced from:
typeinfo for Rectangle in shapes-12a86a.o
"vtable for Shape", referenced from:
Shape::Shape() in shapes-12a86a.o
NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
I assumed that the error speaks for itself and looked up for similar questions, to which I found a lot answers, but could not figure out the mistake in my code... 我以为该错误说明了一切,并寻找了类似的问题,我找到了很多答案,但无法在我的代码中找出错误...
You declared Shape::area
and Shape::rotate
but you did not define them 您声明了
Shape::area
和Shape::rotate
但未定义它们
One solution would be to change shapes.h like this: 一种解决方案是更改shape.h,如下所示:
class Shape {
public:
double h;
double w;
virtual double area(void) { return 0; }
virtual void rotate(void) {}
};
Another solution is to instead add the definitions to shapes.cpp: 另一种解决方案是改为将定义添加到shapes.cpp:
double Shape::area() { return 0; }
void Shape::rotate() {}
As juanchopanza pointed out, another solution is to make the methods pure virtual (which is probably best): 正如juanchopanza所指出的,另一种解决方案是使方法成为纯虚拟方法(这可能是最好的):
class Shape {
public:
double h;
double w;
virtual double area(void) = 0;
virtual void rotate(void) = 0;
};
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