Change an attribute of a base class by the derived class C++

Question

I’m having a problem involving inheritance in C++, I can’t change an attribute of a base class ex:

// classe base
class Base
{
    vector(string) Names; //coloquei entre parenteses porque por algum motivo o string desaparece quando coloco da maneira correta
    public:
        void Add(string);
        string Get(int);
};
void Base::Add(string name)
{
    this->Names.push_back(name);
}
string Base::Get(int name_position)
{
    return this->Names[name_position];
}
// classe derivada
class void Derived : public Base
{
    public:
        void New(string);
};
void Derived::New(string name)
{
    Base::Add(name);
}

What I’m doing on Main is like this

  
Base base;
Derived derived;
derived.New("joao"); 

cout<<base.Get(0);

Can anyone tell me what I am doing wrong, I thought it was possible to change the attribute of a base class using the methods of the base class itself.

Answer 1

There are some errors in your code:

• vector(string) Names; should stay vector<string> Names;.

  To make it work you have to import the respective libraries:

  #include <vector>
  #include <string>
  

  And put the using namespace std or turn each one into std::vector and std::string

• class void Derived : public Base kept his word void more and should become:

  class Derived : public Base
  

• cout<<base.Get(0); what I really wanted to do was cout<<derived.get(0). Note that in your main created two instances:

  Base base;
  Derived derived;
  

  And then assigns the name via the called instance derived:

  derived.New("joao"); 
  

  This is the kind of appeal Derived that derives from Base and so has the vector<Names> inherited. It is at this instance that you must use the method Get that goes to the inherited vector to get the name:

  cout<<derived.Get(0);
  

Your code complete with these fixes would be:

#include <iostream>
#include <vector>
#include <string>

class Base{
    std::vector<std::string> Names;
    public:
        void Add(std::string);
        std::string Get(int);
};
void Base::Add(std::string name){
    this->Names.push_back(name);
}
std::string Base::Get(int name_position){
    return this->Names[name_position];
}
// classe derivada
class Derived : public Base{
    public:
        void New(std::string);
};
void Derived::New(std::string name){
    Base::Add(name);
}

int main(){
    Derived derived;
    derived.New("joao");
    std::cout<<derived.Get(0);

    return 0;
}

See Ideone for the correct result