Invalid initialization of reference type 'Class&' from expression of type 'Class' - class

Question

Ok guys , so I have a list of objects and I want to sort my list by a boolean function I created .
Function ->
bool funct(Student &s1,Student &s2)
{
return s1.calculMedie()<s2.calculMedie();
}
I got this list:
list<Student*> list;
list.push_back(sx[0]);
list.push_back(sx[1]);
list.push_back(sx[2]);
sx is comming from this declaration-> Student **sx=new Student*[3];
I created 3 objects of the type class Student.
I want to sort them by 'calculMedie()' which is a function that returns their average grade.
double Student::calculMedie()
{
int nr=0;
double s=0;
for(auto i : note)
{
nr++;
s=s+i;
}
return s/nr;}
^ thats how it looks.
And when I tried to do a list.sort(list.begin(),list.end(),funct) it gets me this error : " Invalid initialization of reference type 'Class&' from expression of type 'Class'"

Answer 1

It looks like you mixed std::sort algorithm with list<T>::sort method. List can be sorted only by using its sort method.
There are two overloads of list::sort:
void sort();
template< class Compare >
void sort( Compare comp ); // [2]
if you want to sort by comparator, write as follows:
list<Student*> list;
list.sort (funct);
because list stores pointers to Student, you need to modify signature of funct function, it must takes pointers not references:
bool funct(Student* s1,Student* s2)
{
return s1->calculMedie()<s2->calculMedie();
}
good practice is to pass s1,s2 as pointers to const object, when you change s1,s2 to be const Student* s1, const Student* s2 you need also to make calculMedie as const member function.