Confusing in inheritance

I do this excercise:
Implement a sort function that takes a vector of pointers to an interface class, Comparable,
that defines a method, compare(Comparable& other), and returns 0 if the objects are the
same, 1 if the object is greater than other, and -1 if the object is less than other. Create a class
that implements this interface, create several instances, and sort them. If you're looking for
some inspiration for what to create—try a HighScoreElement class that has a name and a
score, and sorts so that the top scores are first, but if two scores are the same, they are sorted
next by name.

I got this error:
E:\Programming\C++\sortFuntionInheritance\main.cpp||In function 'int main()':|
E:\Programming\C++\sortFuntionInheritance\main.cpp|13|error: cannot allocate an object of abstract type 'highScore'|
E:\Programming\C++\sortFuntionInheritance\comparable.h|9|note: because the following virtual functions are pure within 'highScore':|
E:\Programming\C++\sortFuntionInheritance\comparable.h|7|note: virtual int Comparable::compare(Comparable*)|
||=== Build finished: 1 errors, 0 warnings (0 minutes, 0 seconds) ===|

I dont know why compiler said highScore has pure virtual function, plz help correct my program. Thank very much.

main.cpp

 #include <iostream>
#include "comparable.h"

using namespace std;

int main()
{
    char ch = 'y';
    highScore* p_score = NULL;
    vector<Comparable*> v_score;
    while (ch == 'y')
    {
        p_score = new highScore;
        cout << "Input name: ";  cin >> p_score->name;
        cout << "Input score: ";  cin >> p_score->score;
        v_score.push_back(p_score);
        cout << "Do you want to continue? y/n";  cin >> ch;
    }
    sort(v_score);

    return 0;
}

comparable.h

#include <string>
#include <vector>

class Comparable
{
public:
    virtual int compare(const Comparable& other) = 0;
};
class highScore:public Comparable
{
public:
    virtual int compare(const Comparable& other);
    int score;
    std::string name;
};
void sort(std::vector<Comparable*>);

comparable.cpp

#include "comparable.h"

int highScore::compare(const Comparable& other)
{
    if (this->score == other.score || this->name == other.name)
        return 0;
    if (this->score > other.score)
        return 1;
    else
        return -1;
    return this->name.compare(other.name);
}

void sort(std::vector<Comparable*> v_score)
{
    Comparable* temp = NULL;
    //sorting starts by finding the biggest element and changing its pointer with the first element of the list, then finds
    //the second biggest element and changes it pointer with the second element and go on until reach the end of the list
    for (int i = 0, size = v_score.size(); i < size-1; i++)
        for (int j = i+1; j < size; j++)
        {
            if (v_score[i]->compare(v_score[j]) < 0)
            {
                temp = v_score[i];
                v_score[i] = v_score[j];
                v_score[j] = temp;
            }
        }
}

Last edited on

Peter87 (11238)

highScore has not implemented the function int compare(Comparable*).

JLBorges (13770)

And while you are at it, make the function const-correct:

Either: virtual int Comparable::compare( const Comparable* other ) const = 0 ;

or: virtual int Comparable::compare( const Comparable& other ) const = 0 ;

vlad from moscow (6539)

These virtual functions

virtual int Comparable::compare(Comparable* other) = 0;

and

virtual int highScore::compare(highScore& other);

are different functions. The second function does not override the first function.

Last edited on

kradragon94 (32)

i change as above and stuck in making compare function to write out name and score :((

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Confusing in inheritance