Trying to sort Vector of Objects - c++

Question

As the title suggest, I am trying to sort a vector of objects by the GPA. My main issue is putting a method where I define the function for my comparison. The vector itself holds objects of five fields, which includes: string name, string ssn, string year, float credit, float gpa. I know theirs a way to use the sort operator. I am new to C++ so I am not very knowledgeable in this language. I appreciate the help! Here is the code:
#include <iostream>
#include <string>
#include <iterator>
#include <iomanip>
#include <fstream>
#include <vector>
#include <sstream>
#include <algorithm>
#include <cstdlib>
#include <list>
using namespace std;
class Student {
//declare local variables
protected:
string name; //people with names longer than 21 characters will just
have to make do
string ssn; // Social Secturity Number.
float gpa; //Most up to date gpa for the student
float credits; //Number of student's credit hours
//build public methods
public:
//Default Constructor
Student() {}
//Student constructor. Besides the character arrays, everything else is passed by reference.
Student(const string n, const string s, string sGPA, string sCredits) {
name = n;
ssn = s;
gpa = (float)atof(sGPA.c_str());
credits = (float)atof(sCredits.c_str());
}
string getName() {
return name;
}
string getSSN() {
return ssn;
}
float getGPA() {
return gpa;
}
float getCredit() {
return credits;
}
//a function that is expected to be implemented and overridden by subclasses
virtual void print() const {
cout << '\n' << endl;
cout << "Student's name: " << name << endl;
cout << "Student SSN: " << ssn << endl;
cout << "Student's current GPA: " << gpa << endl;
cout << "Student's credit hours: " << credits << endl;
}
// a pure virtual function for implementation later. Makes whole class Abstract
virtual float tuition() const = 0;
};
class Undergrad : public Student {
//declare local variables
protected:
float undergrad_rate = 380.0;
string year;
//build public methods
public:
//Default Constructor
Undergrad() {}
//Undergrad Constructor
Undergrad(const string n, const string s, string uGPA, string uCredits, string y) :
Student(n, s, uGPA, uCredits), year(y) {}
//Display the contents of undergrad
void print() const {
Student::print();
cout << "Undergrad Rate: " << undergrad_rate << endl;
cout << "Year: " << year << endl;
}
//Display undergrad's current year
string get_year() {
return year;
}
//Display the undergrad's current rate
float get_rate() {
return undergrad_rate;
}
//Set a undergrad's current year
void set_year(string y) {
year = y;
}
//Display the cost for an undergrad to attend university
float tuition() const {
return 1000000;
}
};
int main() {
ifstream ip("data.txt");
if (!ip.is_open()) std::cout << "ERROR: File not found" << '/n';
string name;
string ssn;
string year;
string credit;
string gpa;
list<Undergrad> myList;
list<Undergrad>::iterator i;
//Undergrad g(name, ssn, year, credit, gpa);
while (ip.good()) {
getline(ip, name, ',');
getline(ip, ssn, ',');
getline(ip, gpa, ',');
getline(ip, credit, ',');
getline(ip, year, '\n');
// float number = stoi(gpa);
//float number1 = stoi(credit);
Undergrad g(name, ssn, year, credit, gpa);
myList.push_back(g);
}
ip.close();
//This deletes the last object in the list and stores it in a temp object. It assigns that object to the beginning of the list.
Undergrad temp = myList.back();
myList.pop_back();
myList.insert(myList.begin(), temp);
/* for (int i = 0; i < myList.size(); i++) {
cout << "Name: " << myList[i].getName() << endl;
cout << "SSN: " << myList[i].getSSN() << endl;
cout << "Year: " << file[i].get_year() << endl;
cout << "Credit: " << file[i].getCredit() << endl;
cout << "GPA " << file[i].getGPA() << endl;
cout << " " << endl;
}
*/
/*for (Undergrad &x : myList) { //Goes through my list and displays its contents
x.print(); //This isn't bringing up errors.
}
*/
//This code copy the contents of the list to a vector.
std::vector<Undergrad> vect{ std::make_move_iterator(std::begin(myList)),
std::make_move_iterator(std::end(myList)) };
std::sort(vect.begin(), vect.end(), CompareGPA);
for (Undergrad &x : vect) {
x.print();
}
system("pause");
return 0;
}
Furthermore this is the code Im trying to implement to get the comparision
bool CompareGPA(const Student& left, const Student& right) {
return left.gpa > right.gpa;
}

Answer 1

Using lambda you can implement like this:Use a property int get_gpa() const to access the protected member.
std::sort(vect.begin(), vect.end(), [] (const Student& left, const Student& right)
{
return left.get_gpa() > right.get_gpa();
});
Here how to implement the property ( a member function to return the protected variable) :
int get_gpa() const
{
return gpa;
}