How to pass a function as parameter in class(C++)

Question

I am doing Sort a List Of Student via: 1.Via Name 2.Via Date Of Birth Both only differ type of compare,the rest is the same. Because I do not want duplicate code I have used template type to do this:

class Student
{
    Date date;  // Date is a class
    Name name;  // Name is a class
   public:
    Date getDate() { return date; }
    Name getName() { return name; }
};
class ListOfStudent
{
    vector<Student> List;

   public:
    bool CompareDate(Date &d1, Date &d2);  // define d1<d2
    bool CompareName(Name &n1, Name &n2);  // define n1<n2

    void SortViaName()
    {
        for (int i = 0; i < List.size(); ++i)
            int min = i;
        for (int j = i + 1; j < List.size(); ++j)
        {
            if (CompareName(List[j].getName(), List[min].getName()))
                min = j;
        }
        if (min != i)
            swap(List[i], List[min]);
    }

    void SortViaDate()
    {
        for (int i = 0; i < List.size(); ++i)
            int min = i;
        for (int j = i + 1; j < List.size(); ++j)
        {
            if (CompareName(List[j].getDate(), List[min].getDate()))
                min = j;
        }
        if (min != i)
            swap(List[i], List[min]);
    }

    // Because i do not want to duplicate code so I do:
    template <typename T>
    void Sort(bool (*f)(T, T), T (*t)())
    {
        for (int i = 0; i < List.size(); ++i)
            int min = i;
        for (int j = i + 1; j < List.size(); ++j)
        {
            if ((*f)(DS[j].(*t)(), List[i].(*t)()))
                min = j;
        }
        if (min != i)
            swap(List[i], List[min]);
    }
};

It has something wrong at template function so I need your supports.

Answer 1

In order to make things generic, the simplest way to set things up is to make the CompareThing function optionally take a Student& instead of a Date or Name.

Note: CompareDate and CompareName should be either static or global, that way you can pass them around as function pointers.

// We'll keep these
// Also they should either be static or global
bool CompareDate(Date &d1,Date &d2); //define d1<d2
bool CompareName(Name &n1,Name &n2); //define n1<n2

// Because these can both be used with Student, it's easy to template over them
bool CompareDate(Student &s1, Student &s2) {
    return CompareDate(s1.getDate(), s2.getDate()); 
}
bool CompareName(Student &s1, Student &s2) {
    return CompareName(s1.getName(), s2.getName()); 
}

Then, we can write Sort like this:

void Sort(bool(*compare)(Student&, Student&)) {
    std::sort(List.begin(), List.end(), compare); 
}
void SortViaName() {
    Sort(CompareName); 
}
void SortViaDate() {
    Sort(CompareDate); 
}

Using your selection sort

We can write Sort to take the function as a parameter, and then use your selection sort instead of std::sort:

void Sort(bool (*compare)(Student&, Student&))
{
    for (int i = 0; i < List.size(); ++i) {
        int min = i;
        for (int j = i + 1; j < List.size(); ++j)
        {
            if (compare(List[j].getName(), List[min].getName()))
                min = j;
        }
        if (min != i)
            swap(List[i], List[min]);
    } 
}