c – g“因为以下虚函数是纯粹的”具有抽象基类

这是我的示例代码,它产生错误：

struct Impl
{
  int data_size_;
  int find(int var){return 0;}
  int get(int rowid){return 0;}
};

class Container
{
public:
  Container() {}
  virtual ~Container() {}
  virtual int get_size() = 0;
  virtual int get(int rowid) = 0;
};


class SortedContainer : virtual public Container {
public:
  virtual int find(int var) = 0;
};

class ContainerImpl : public Container
{
protected:
  Impl impl_;
public:
  int get_size() {return impl_.data_size_;}
  int get(int rowid) {return impl_.get(rowid);}
};

class SortedContainerImpl
  : public SortedContainer,public ContainerImpl
{
private:
  typedef ContainerImpl Base;
public:
  int find(int var){return Base::impl_.find(var);}
};

ContainerImpl ci;
SortedContainerImpl sci;

似乎“SortedContainerImpl”出错,而“ContainerImpl”没问题.

抱怨：

example_b.cpp:42:21: error: cannot declare variable ‘sci’ to be of abstract type ‘SortedContainerImpl’
example_b.cpp:32:7: note:   because the following virtual functions are pure within ‘SortedContainerImpl’:
example_b.cpp:13:15: note:  virtual int Container::get_size()
example_b.cpp:14:15: note:  virtual int Container::get(int)

我从ContainerImpl获取SortedContainerImpl以重用get_size()和get(int)

我不熟悉c,这个问题的本质是什么,我该如何解决？

谢谢大家.

解决方法

您的SortedContainerImpl类有两个单独的Container基类.一个是虚拟的(通过SortedContainer类),另一个是非虚​​拟的(通过ContainerImpl类).

SortedContainerImpl具有Container :: get_size()和Container :: get(int)的具体实现,用于来自ContainerImpl的基础,但不适用于通过SortedContainer进入的虚拟基础.

解决问题的一种方法是在SortedContainerImpl中给出具体实现：

class SortedContainerImpl
  : public SortedContainer,public ContainerImpl
{
private:
  typedef ContainerImpl Base;
public:
  int find(int var){return Base::impl_.find(var);}

  int get_size() {return ContainerImpl::get_size();}
  int get(int rowid) {return ContainerImpl::get(rowid);}
};

另一种方法是使Container成为ContainerImpl的虚拟基类,因此SortedContainerImpl只能获得一个虚拟的基础容器：

class ContainerImpl : virtual public Container
{
protected:
  Impl impl_;
public:
  int get_size() {return impl_.data_size_;}
  int get(int rowid) {return impl_.get(rowid);}
};