c++以泛型方式对对象类数组进行排序

Question

晚上好，专家

我正在以通用的方式进行编程练习。我知道如何用不同的数据类型对不同的对象进行排序，但我很难对类进行排序

这是我的代码：

#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;
}

当我调用selectionSort函数时，编译器会给我以下错误：

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:usersgulmiradocumentsvisual studio 2010projectscsci203_lab1csci203_lab1task6.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:usersgulmiradocumentsvisual studio 2010projectscsci203_lab1csci203_lab1task6.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:usersgulmiradocumentsvisual studio 2010projectscsci203_lab1csci203_lab1task6.cpp  74

请提出如何解决这个问题的想法，感谢提前

Answer 1

正如错误所指出的，Employee没有operator<，但您正试图在排序函数中使用它
您需要选择一个订购条件（例如按员工id编号），并相应地实现operator<。

例如：

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

如果你想让调用者选择排序标准，你可以像std::sort()一样，允许传递一个用于比较的函子或函数指针：

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

然后你可以这样使用：

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);

Answer 2

您需要实现<员工类的操作员。不要指望编译器知道如何为你做这件事。你需要告诉它你希望那个操作符为类做什么。