从派生的模板类调用函数 [英] Calling a function from a derived template class

问题描述

我的基类：

//Element.h
class Element
{
public:
Element();
virtual ~Element(){}; // not sure if I need this

virtual Element& plus(const Element&);
virtual Element& minus(const Element&);
};

派生模板类：

//Vector.h
#include "Element.h"

template <class T>
class Vector: public Element {
T x, y, z;

public:
//constructors
Vector();
Vector(const T& x, const T& y = 0, const T& z =0);
Vector(const Vector& u);
...     
//operations
Element& plus(const Element&) const;
Element& minus(const Element&) const;
...
};
...

//summation
template <class T>
Element& Vector<T>::plus(const Element& v) const
{
const Vector<T>& w = static_cast<const Vector<T>&>(v);  
Vector<T>* ret = new Vector<T>((x + w.x), (y + w.y), (z + w.z));
return *ret;
}

//difference
template <class T>
Element& Vector<T>::minus(const Element& v) const
{
const Vector<T>& w = static_cast<const Vector<T>&>(v);
Vector<T>* ret = new Vector<T>((x - w.x), (y - w.y), (z - w.z));
return *ret;
}

我在此代码中遇到了另一个问题（在另​​一篇文章），但目前我正在努力解决这样一个事实：如果我试图运行它，我得到

I had another issue with this code (answered in another post), but currently I'm wrestling with the fact that if I try to run this, I get

未定义的符号：
Element ::加（元素const&），引用自：
vtable for Vectorin main.o

Element :: Element（），引用自：
在main.o中的Vector :: Vector（）

在main.o中的Vector :: Vector（double const&，double const&，double const&）

Element :: minus （元素const&），引自：
vtable for Vectorin main.o

typeinfo for Element，引用自：
typeinfo for Vectorin main .o

ld：未找到符号

collect2：ld返回1退出状态

Undefined symbols: "Element::plus(Element const&)", referenced from:
vtable for Vectorin main.o
"Element::Element()", referenced from:
Vector::Vector()in main.o
Vector::Vector(double const&, double const&, double const&)in main.o
"Element::minus(Element const&)", referenced from:
vtable for Vectorin main.o
"typeinfo for Element", referenced from:
typeinfo for Vectorin main.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

这是因为e派生的模板类不与基类放在同一个文件中，这会导致编译器问题（类似于我在头文件中定义整个Vector类的方式）？

Is this because the derived template class isn't housed in the same file as the base class, and that's causing compiler issues (similar to how I had to define the entire Vector class in the header file)?

我对C ++很新，还在阅读vtable是什么以及它们是如何工作的，但是我还不能理解这一点。

I'm fairly new to C++, and still reading up on what vtables are and how they work, but I can't quite figure this out yet.

推荐答案

我认为编译器/链接器在它告诉你未定义的符号时意味着它：Element :: plus（Element const&）。这些符号（元素的加号和减号）已经声明，但尚未定义。

I think the compiler/linker means it when it tells you Undefined symbols: "Element::plus(Element const&)" . These symbols (plus and minus for Element) have been declared but they have not been defined.

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