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);}
};
