C++ accelerated (Q 8-1) - Template function parameterised by another function

[CppLiz]

I've seen a few posts on here about the use of template functions and about questions from the book C++ Accelerated (Koeing/Moo) but none of them answer my questions so I'm hoping you can help.

The question I am struggling with is; "The various analysis functions we wrote is Sect 6.2/110 share the same behaviour; they differ only in terms of the functions they call to calculate the final grade. Write a template function, parameterized by the type of the grading function, and use that function to evaluate the grading schemes. "

I'm still in the early stages of learning, and I would really appreciate some help with this question as I have been stuck on it for weeks and no amount of Googling has helped. Everything I have read refers to referencing, or pointers - which the book has not yet covered so I find it even more confusing.

The 3 analysis functions are all very similar - included below - and I think the question is asking me to write a template function that will replace all 3. I have written a function that I think might work - see below - but I am getting errors when I try to compile because the function write_analysis that uses all of the original analysis functions can not cope with my template function.

I am completely stuck and would really appreciate any help.

I have tried not to include to much code to start with so I hope the below is sufficient.

  double median_analysis(const vector<Student_info>& students)
{
  vector<double> grades;
  transform(students.begin(), students.end(),back_inserter(grades), grade_aux);

  return median(grades);
}



double optimistic_median_analysis(const vector<student_info>& students){

vector<double> grades ; 

transform(students.begin(), students.end(), back_inserter(grades), optimistic_median) ;

return median(grades) ; 

}


double average_analysis(const vector<Student_info>& students)
{
 vector<double> grades;
 transform(students.begin(), students.end(),back_inserter(grades), average_grade) ;

 return median(grades);
 }

My attempt at a solution is;

template <typename F > double Tanalysis(F Func(const student_info&))
{

std::vector<double> grades ; 

transform(students.begin(), students.end(), back_inserter(grades), Func) ;

return median(grades) ;
 }

The Write_analysis function that is causing my current problem is;

    void write_analysis(ostream& out, const string& name, 
                double analysis(const vector<student_info>&), 
                const vector<student_info>& did, 
                const vector<student_info>& didnt){

    out << name << " : median(did) = " << analysis(did) <<
                   " : median(didnt) = " << analysis(didnt) << endl ; 

     }

This is my first time posting so I hope the content is sufficient and the format ok. Sorry if it is not, but any help would be appreciated.

[cire]

Something like:

template <typename func_type>
double do_analysis(const vector<Student_info>& students, func_type f)
{
    vector <double> grades;
    transform(students.begin(), students.end(), back_inserter(grades), f);

    return median(grades);
}

[CppLiz]

Thank you!

I managed to find my way to a solution in the end and thought I would share in case anyone else gets equally stuck on this one.

#include<vector>
#include<algorithm> //transform 

#include "student_info.h"
#include "median.h"

template <typename F> 
double Tanalysis(F Func, std::vector<student_info> students)
{
    std::vector<double> grades ; 

   transform(students.begin(), students.end(), back_inserter(grades), Func) ;

   return median(grades) ;
}

The above template works by itself in main.cpp called as follows;

double ans = Tanalysis(grade_aux,did) ;
double ans2 = Tanalysis(grade_aux, didnt) ; 

cout << "And the Answer for did is: " << ans <<
    ". The Answer for didnt is: " << ans2 << endl ;

To get it to work with the write_analysis function I had to template that as well.

template <typename F, typename F2>
void Twrite_analysis(ostream& out, const string& name, F Func, F2 Func2)
{
    out << name << " : median(did) = " << Func <<
                   " : median(didnt) = " << Func2 << endl ; 
}

called as follows in main.cpp;

Twrite_analysis(cout, "median", Tanalysis(grade_aux, did), Tanalysis(grade_aux, didnt));

This was the best solution I could come up with, but if anyone has any comments on how to improve it that would be good.