访问抽象类派生类的抽象类的向量！ 怎么样？

Question

ACTUAL PROBLEM: have an Abstract Class operations that inherits from VAR Class , which then all the operations derived class(out,sleep,Add) inherit from the operations class. FSM Class inherits from Var also, so That I want one instance of VAR class inside my program.

I am trying to make vector < pair< string, int>> var as a shared data between the FSM class and the Operations class and its deviates . I initialized the var in the main through the FSM class .

Each time we call the exist function in VAR through Class operation , it returns it doesn't exits cause it is empty ! How can I overcome this?

#include <iostream>
#include <string>
#include <vector>
#include <fstream>
using namespace std;
class VAR
{
public:vector<pair<string, int>> var;
    VAR()
    {}
 ~VAR(){}
void createVar(string x,int y)
    {}
void setVarValue(string& x, int y)
    {}
int getVarValue(string x){}
 bool exits(string& name)
    {}
class operations : virtual public VAR
{
public:
    operations()
    {}
void virtual excute() = 0;    
};
class Out :public virtual operations
{
};
class Add :public  virtual operations
{
};

class FSM :public virtual VAR, public virtual transition
    {
       void intialize()
        {
            createVar("X", 1);
            createVar("Y", 5);
        }
    };
void main()
{
FSM x;
pair<state, vector<pair<state, int>>> p1;
pair<state, int>p2;
x.intialize();

p2.first.name = "b";
p2.second = 3;
p1.first.name = "a";

p1.second.push_back(p2);
x.trans.push_back(p1);

x.trans[0].first.instructionList.push_back(new Add("X=X+Y"));
x.trans[0].first.instructionList.push_back(new Out("X"));
x.trans[0].first.exec_all();//wrong output cause exist() returns false
}

Answer 1

Not all shapes are usefully characterised by a length, so it doesn't make sense to want to get the length of all shapes. For example, a circle might have a radius or a diameter, but talking about the length of a circle would get blank looks from most people.

The usual point of a base class is that it provides functionality that are relevant to all shapes. So a member function like draw() may be relevant to all shapes (albeit, as a virtual function, each derived class can implement specifics of how it is drawn) but functions like setLength() and getLength() may not be.

Generally speaking, when starting from a pointer to base, if you need to convert it to a derived type, that is usually considered a sign of a broken design (and not just by C++ practitioners). What you really need to do is work out the set of capabilities the shape class really needs to provide, and make them general enough so it can handle the need for some specialised shapes to have a length, and a need for some other specialised shapes not to have a length.

It's hard to give a more specific answer than that as your needs (and therefore the set of capabilities your shape class needs to provide) will be specific to your application.

Oh: main() returns int , not void in standard C++. Your compiler may support void main() , but not all do, so it is usually considered a bad idea to use it.