c++ sort array of objects classes in generic way

Question

Good evening, experts

I am working on the exercise in programming in generic way. I understood how to to sort the different objects with different data types, however I am struggling how to sort classes

here is my code:

#include <iostream>
#include<string>
using namespace std;

class Employee
{
private:
    int idNum;
    string lastName;
    int hireDate;
    int verifyDate(int);
public:
    Employee();
    Employee(int,string,int);
    void displayData();
    void setLastName(string);
    void setIdNum(int);
    void setHireDate(int);
    void setGradePointAverage(double);
};

Employee::Employee()
{
    idNum=0;
    lastName="";
    hireDate=0;
}

Employee::Employee(int idNum, string lastName, int hireDate)
{
    this->idNum=idNum;
    this->lastName=lastName;
    this->hireDate=hireDate;
}

void Employee::displayData()
{
    cout<<"\nEmployee Data:";
    cout<<"\nID: "<<idNum;
    cout<<"\nLastName: "<<lastName;
    cout<<"\nHireDate: "<<hireDate;
}

void Employee::setLastName(string lastName)
{
    this->lastName=lastName;
}

void Employee::setIdNum(int idNum)
{
    this->idNum=idNum;
}

void Employee::setHireDate(int hireDate)
{
    this->hireDate=hireDate;
}

void Employee::setGradePointAverage(double grade)
{
    double new_grade;
    new_grade=grade;
}



template <class T>
void selectionSort (T data[], int n){
    T temp;
    for(int i=0, j, least; i < n-1; i++){
        for( j = i+1, least = i; j < n; j++ ){
            if ( data[j] < data[least]){
                least = j;
            }
        }
        temp = data[least];
        data[least] = data[i];
        data[i] = temp;
    }
}


int main()
{
    Employee e[3];

    e[0].setIdNum(337322);
    e[1].setIdNum(3539854);
    e[2].setIdNum(1224567);

    e[0].setLastName("Marlen");
    e[1].setLastName("Oleg");
    e[2].setLastName("Test");

    e[0].setHireDate(25061989);
    e[1].setHireDate(30001990);
    e[2].setHireDate(12122012);

    for (int i=0; i<3;i++)
    {
        e[i].displayData();
        cout<<"\n";
    }

    selectionSort(e,3);




    return 0;
}

when i call my selectionSort function the compiler gives me the following errors:

Error   1   error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const _Elem *)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'Employee'   c:\users\gulmira\documents\visual studio 2010\projects\csci203_lab1\csci203_lab1\task6.cpp  74
Error   2   error C2784: 'bool std::operator <(const _Elem *,const std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'const _Elem *' from 'Employee' c:\users\gulmira\documents\visual studio 2010\projects\csci203_lab1\csci203_lab1\task6.cpp  74
Error   3   error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'Employee' c:\users\gulmira\documents\visual studio 2010\projects\csci203_lab1\csci203_lab1\task6.cpp  74

Please suggest an idea for how to solve this, Thanks in Advance

Georg Fritzsche · Accepted Answer · 2012-02-11 17:22:35Z

2

As the error points out, there is no operator< for Employee, but you are trying to use it in your sorting function.
You need to choose an ordering criteria (e.g. numerically by employee id) and implement operator< accordingly.

E.g.:

bool Employee::operator<(const Employee& rhs) const { 
    return idNum < rhs.idNum; 
}

If you want to give the caller the choice of the ordering criteria, you can do it like std::sort() by allowing a functor or function pointer to be passed that will be used for the comparisons:

template <class T, class Comp>
void selectionSort (T data[], int n, Comp comp){
    // ...
    if (comp(data[j], data[least])) {
    // ...

... which you could then e.g. use like this:

bool orderEmployeesByLastName(const Employee& a, const Employee& b) {
    return std::lexicographical_compare(
               a.getLastName().begin(), a.getLastName.end(), 
               b.getLastName().begin(), b.getLastName.end());
}

// ... 
selectionSort(e, 3, &orderEmployeesByLastName);

edited Feb 11, 2012 at 17:22

answered Feb 11, 2012 at 17:02

Georg Fritzsche

99.4k26 gold badges198 silver badges238 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

mydreamadsl Over a year ago

so as i understood do i need to overload operators? and how can i access i sort numerically and access it?

mydreamadsl Over a year ago

so how I can sort by names if already defined operator > to sort by numbers?

MGZero · Accepted Answer · 2012-02-11 17:05:35Z

1

You need to implement the < operator for your employee class. Don't expect the compiler to know how to do this for you. You need to tell it what you want that operator to do for the class.

answered Feb 11, 2012 at 17:05

MGZero

6,0225 gold badges33 silver badges47 bronze badges

Collectives™ on Stack Overflow

c++ sort array of objects classes in generic way

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related