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

Answer 1

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);