cannot instantiate abstract class error [duplicate] - c++

Question

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Adding Elements to std::vector of an abstract class
(4 answers)
Closed 5 years ago.
I have a problem with my code.
I have three classes, and one of them is a pure abstract class. I don't know why I receive the error:
'note' cannot instantiate abstact class.
It may be because of STL usage, or I have made a mistake and I dont see it.
The problem is I tried without STL and it works, and I don't know what is the problem here because I think it it correct.
#pragma once
class note
{
protected:
int ziua;
int ora;
public:
note();
note(int day,int hour);
virtual void print()=0;
virtual ~note();
};
#include "note.h"
note::note()
{
}
note::note(int day, int hour) :ziua(day), ora(hour)
{
}
note::~note()
{
}
#pragma once
#include "note.h"
#include <iostream>
class apeluri:public note
{
char *numar_telefon;
public:
apeluri();
apeluri(int day, int h, char*phone);
void print()
{
printf("%d %d %s", ziua, ora, numar_telefon);
}
~apeluri();
};
#pragma once
#include <iostream>
#include "apeluri.h"
#include <vector>
#include "note.h"
using namespace std;
class remainder
{
vector<note> t;
public:
remainder();
void addsedinta(int zi, int ora, int durata, char*subi);
void addapel(int zi, int ora, char*phon)
{
apeluri *f;
f = new apeluri(zi, ora, phon);
t.push_back(*f);
}
void show()
{
}
~remainder();
};

Answer 1

In your remainder class, using vector<note> is illegal. note is abstract, so the vector can't create note objects.
Even if note were not abstract, your code would still not work correctly, because it would be affected by object slicing.
To store derived objects in a container of base classes, you must use pointers instead, ie vector<note*>:
#pragma once
#include <iostream>
#include <vector>
#include "note.h"
#include "apeluri.h"
using namespace std;
class remainder
{
private:
vector<note*> t;
remainder(const remainder &) {}
remainder& operator=(const remainder &) { return *this; }
public:
remainder();
~remainder()
{
for(std::vector<note*>::iterator i = t.begin(); i != t.end(); ++i) {
delete *i;
}
}
void addsedinta(int zi, int ora, int durata, char*subi);
void addapel(int zi, int ora, char*phon)
{
apeluri *f = new apeluri(zi, ora, phon);
t.push_back(f);
}
void show()
{
}
};
If you are using C++11 or later, this would be better written as this instead:
#pragma once
#include <iostream>
#include <vector>
#include <memory>
#include "note.h"
#include "apeluri.h"
using namespace std;
class remainder
{
private:
vector<unique_ptr<note>> t;
public:
remainder();
remainder(const remainder &) = delete;
remainder& operator=(const remainder &) = delete;
void addsedinta(int zi, int ora, int durata, char*subi);
void addapel(int zi, int ora, char*phon)
{
t.push_back(std::unique_ptr<apeluri>(new apeluri(zi, ora, phon)));
// in C++14 and later, use this instead:
// t.push_back(std::make_unique<apeluri>(zi, ora, phon));
}
void show()
{
}
};