如何通过封闭 class 访问嵌套的 class 成员 function，其中所有成员在 Z6CE809EACF90BA125B40FA4BD9

Question

I am using nested classes in a sensor library development and running into errors. Below is sample code and explanation.

MainClass.cpp

class MainClass
{
 public:      
     class nested_class;
     void func1(){
       nested_class1.print();
     }
};

NestedClass.cpp

class MainClass::nested_class
{
 public:
      virtual void print() = 0;
};

Nested1.cpp

class nested_class1: virtual public MainClass::nested_class{
    public:
        void print();
};
void nested_class1::print(){
        cout<<"This is for 1\n";
    }

Nested2.cpp

class nested_class2 : virtual public MainClass::nested_class{
    public:
    void print(){
        cout<<"This is  for 2";
    }
};

I am trying to use it to extend the concept of abstraction in my sensor library. But on doing so following is the error: print() was not declared in this scope .

I am newbie to this concept and hence having a hard time finding the issue here. Where am I going wrong here? I can provide more details if required.

Thanks in advance!

Answer 1

nested_class1.print(); isn't how you'd call the print member of an instance of nested_class1 , even if it were declared before there.

The definition of MainClass::func1 must be after the definition of nested_class1 , which must be after the definition of MainClass::nested_class .

#include <iostream>

class MainClass
{
 public:      
     class nested_class;
     void func1();
};

class MainClass::nested_class
{
 public:
      virtual void print() = 0;
};

class nested_class1: virtual public MainClass::nested_class{
    public:
    void print();
};

class nested_class2 : virtual public MainClass::nested_class{
    public:
    void print();
};

void MainClass::func1() {
   nested_class1 obj;
   obj.print();
}

void nested_class1::print(){
    std::cout<<"This is for 1\n";
}

void nested_class1::print(){
    std::cout<<"This is  for 2";
}

int main(){
    MainClass instance;
    instance.func1();
}

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