std::sort error using custom classes - c++

Question

I have looked through stackoverflow and added an overload operator to hopefully make it work with sort. Though I still get an explosion of an error saying something is wrong with sort.
Code:
#include <iostream>
#include <vector>
#include <ctime>
#include <cstdlib>
#include <algorithm>
class Student
{
private:
std::string name_;
int number_;
std::vector<int> grades_;
const int num_courses_;
static std::string gen_name() {
return std::to_string(rand());
}
static int gen_number() {
return rand() % (201600000 - 201100000 + 1) + 201100000;
}
static int gen_grade() {
return rand() % (100 - 70 + 1) + 70;
}
double compute_average() {
int marks = 0;
int count = 0;
for (std::vector<int>::iterator i = grades_.begin(); i != grades_.end(); i++, count++){
marks += *i;
}
return static_cast<double>(marks) / count;
}
public:
Student() : name_(gen_name()), number_(gen_number()), num_courses_(5)
{
for (int i = 0; i < num_courses_; ++i) {
grades_.push_back(gen_grade());
}
}
double getAvg() {
return compute_average();
}
friend std::ostream& operator<<(std::ostream& os, Student& s) {
os << "Name = " << s.name_ << "\tNumber = " << s.number_ << "\tAvg = " << s.compute_average();
return os;
}
std::string getName() {
return name_;
}
void print_grades(std::ostream& os) const
{
for (int i = 0; i < num_courses_; ++i) {
os << grades_[i] << ", ";
}
}
bool operator < (const Student& str) const
{
return (name_ < str.name_);
}
};
int main(int argc, char ** argv) {
srand(time(NULL));
if (argc == 2){
int numbOfStudents = atoi(argv[1]);
std::vector<Student> studentVec;
for (int i = 0; i < numbOfStudents; i++){
studentVec.push_back(Student());
}
std::sort(studentVec.begin(), studentVec.end());
for (std::vector<Student>::iterator xi = studentVec.begin(); xi != studentVec.end(); xi++) {
std::cout << *xi << std::endl;
}
}
else{
std::cout << "Usage: " << argv[0] << " {numb} " << std::endl;
}
return 0
}
The error comes when I run sort (I know it's sort since if I comment it out, it works properly). With the error code
In file included from /usr/include/c++/4.9/algorithm:62:0,
from main.cpp:5:
/usr/include/c++/4.9/bits/stl_algo.h: In instantiation of ‘void std::__insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Student*, std::vector<Student> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’:
/usr/include/c++/4.9/bits/stl_algo.h:1884:70: required from ‘void std::__final_insertion_sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Student*, std::vector<Student> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’
/usr/include/c++/4.9/bits/stl_algo.h:1970:55: required from ‘void std::__sort(_RandomAccessIterator, _RandomAccessIterator, _Compare) [with _RandomAccessIterator = __gnu_cxx::__normal_iterator<Student*, std::vector<Student> >; _Compare = __gnu_cxx::__ops::_Iter_less_iter]’
/usr/include/c++/4.9/bits/stl_algo.h:4685:72: required from ‘void std::sort(_RAIter, _RAIter) [with _RAIter = __gnu_cxx::__normal_iterator<Student*, std::vector<Student> >]’
main.cpp:79:50: required from here
/usr/include/c++/4.9/bits/stl_algo.h:1851:17: error: use of deleted function ‘Student& Student::operator=(Student&&)’
*__first = _GLIBCXX_MOVE(__val);
I searched earlier which helped me get to the result of adding a '<' overload, though I still get an error. Can anyone help point out where the mistake is? Thank you. (I compile using g++ --std=c++11)

Answer 1

the member variable const int num_courses_; is const, which means it must be set in the initializer list of the constructor.
num_courses_ can't be set by the copy assignment operator Student& Student::operator=(Student&&), so it prevent the compiler from generating the copy assignment operator for that class. Since there's no copy assignment operator available, and the std::sort function needs it to work, the compilation fails and complains about the copy assignment operator not being available.
Simply remove the const and declare the variable as int num_courses_ and your code should work.