How can change the value of a member of a base class?-CodePudding

I have three classes:

class Operation{
public:
    virtual bool execute(const Solution& sol, Solution& newSol) = 0;
    pair<int, int> pair_routes;
};

class OperationR : public Operation{
public:
    OperationR(){};
    bool execute(const Solution& sol, Solution& newSol);
    pair<int, int> pair_routes;
};

class OperationD : public Operation{
public:
    OperationD(){};
    bool execute(const Solution& sol, Solution& newSol);
    pair<int, int> pair_routes;
};

The value of pair_routes changes inside the execute() function.

In the main() function, I create a vector of class Operation like this:

vector<Operation*> operations;
    
OperationR* opr = new OperationR();
operations.push_back(opr);
    
OperationD* opd = new OperationD();
operations.push_back(opd);
    
Operation* op = operations[0];
Solution s1, s2;
op->execute(s1, s2);   // line 1
    
cout << op->pair_routes.first;

There is no problem in the compilation, but even if the value of pair_routes changes in line 1, it returns the value 0. I tried to initialize this member in the base class with different values, and each time the program returns this value.

CodePudding user response：

Your derived classes are declaring their own pair_routes members that shadow (ie, hide) the pair_routes member of the base Operation class.

When you execute op->execute(), op is pointing at an OperationR object, so it is calling OperationR::execute(), which is then modifying the OperationR::pair_routes data member. But then afterwards, you are display the Operation::pair_routes data member instead, which was not modified.

Get rid of the shadowing pair_routes data members, you don't need them. The derived classes have access to the pair_routes data member of the base class.

class Operation{
public:
    virtual bool execute(const Solution& sol, Solution& newSol) = 0;
    pair<int, int> pair_routes;
};

class OperationR : public Operation{
public:
    OperationR() = default;
    bool execute(const Solution& sol, Solution& newSol) override;
    //pair<int, int> pair_routes; // <-- get rid of this
};

class OperationD : public Operation{
public:
    OperationD() = default;
    bool execute(const Solution& sol, Solution& newSol) override;
    //pair<int, int> pair_routes; // <-- get rid of this
};