c++ - 继承错误 - 无法实例化抽象类\无法访问类中声明的 protected 成员

Question

我对这种继承概念有点陌生，我无法弄清楚哪里出了问题。我很乐意提供一些帮助。

所以我有三个类(class)和一个主类(class):

class BaseClassPipeline
{
 protected:
   BaseClassPipeline::BaseClassPipeline(void){};
   virtual int executeFilter  (SRV *p_Srv) = 0;
   BaseClassPipeline::~BaseClassPipeline(void){};
};


class filter_A:public BaseClassPipeline
{
**edit: protected and not public**
 **public:**
   filter_A:::filter_A(void);
   int filter_A::executeFilter (SRV *p_Srv){return 1}
   filter_A:::~filter_A(void);
};



class PipelineAttr
{

protected:
    PipelineAttr::PipelineAttr(FILE *cfgFile, SRV *p_Srv){...};
    BaseClassPipeline** PipelineAttr::createPipeline(FILE *cfgFile){...};
    int PipelineAttr::getNumOfFilters(){...};
    PipelineAttr::~PipelineAttr(void){...};
};



class Pipeline:public BaseClassPipeline, public PipelineAttr
{
public:
   Pipeline::Pipeline(FILE *cfgFile, SRV *p_Srv) : PipelineAttr(cfgFile, p_Srv){}
    int Pipeline::executePipeline(SRV *p_Srv);
    int Pipeline::countFilters();
   Pipeline::~Pipeline(void);
};

这是主要的:

void main()
{
 ...
 Pipeline pipe(cfgFile, srv); // trying to create instance of pipeline
}

我尝试阅读其他一些帖子，但无法弄清楚我做错了什么。

我收到这些消息:

'Pipeline' : cannot instantiate abstract class

'filter_A::filter_A' : cannot access protected member declared in class 'filter_A'

谢谢。

Answer 1

“管道”:无法实例化抽象类

您继承自抽象基类 BaseClassPipeline。这意味着如果您不覆盖该类的纯虚函数，那么您的派生类也将是抽象的。

class Pipeline:public BaseClassPipeline, public PipelineAttr
{
public:
   Pipeline::Pipeline(FILE *cfgFile, SRV *p_Srv) : PipelineAttr(cfgFile, p_Srv){}
   int executeFilter  (SRV *p_Srv) {}        <<<< Now, you have provided the definition.

“filter_A::filter_A”:无法访问类“filter_A”中声明的 protected 成员

定义 filter_A 的正确语法是:-

class filter_A:public BaseClassPipeline
{
 public:
   filter_A();
   int executeFilter (SRV *p_Srv) { return 1; }
   ~filter_A();
};