Using sort for a class vector with private variables

Question

i have a class

class Studentas
{
 public:
 static const int CPaz=10;
 private:
 string pavarde, vardas, grupe;
 double paz[CPaz],   // paþymiø masyvas
 np;          // paþymiø kiekis
 double vidurkis;
 double STsk;
 public:
 Studentas(): pavarde(""), vardas(""), grupe(""), np(0), STsk(1),vidurkis(0)
 { }
 double imtinp(){return np;}
 double imtipaz(int i){return paz[i];}

 void Deti(string pav, string vard, string grup, int np, int pz[],double vid);
 void grupeDETI(string grp,double vidurk){grupe=grp;vidurkis+=vidurk;}

 double iv(){return vidurkis;} <---------------------------------------THE ONES IM USING
 void isvestiVID(){vidurkis/=STsk;}
 void pridetiSK(){STsk++;}

 string ig(){return grupe;} <---------------------------------------THE ONES IM USING
 string Spausdinti(int i);
 string SpausdintiGrupes();
};

the bool i was using bool

myfunction(Studentas const &d1,Studentas const &d2){return (d1.iv() > d2.iv() || d1.iv()==d2.iv()     && d1.ig() < d2.ig());} 

vector<Studentas> grupe;(with whatever length)

sort(grupe.begin(), grupe.end(),myfunction);

and i get an error, " cannot convert 'this' pointer from 'const Studentas' to 'Studentas &' "

EDIT : i use void functions to get my variables.

EDIT2: thanks for all the help, i think i'll just bubble this one out.Dont have the time to waste, thanks again for the help.

EDIT3: dun goofed on my operator overlays, the method below works.

Make `ig` and `iv` `const` so you can use those with `const` objects. You might also want to implement `>`, `<`, and `==` instead of needing to provide access to private members. — crashmstr, Oct 09 '14 at 14:52

score 3 · Accepted Answer · answered Oct 09 '14 at 14:51

3

Mark your methods as const:

double iv() const {return vidurkis;}

This way you'll be able to call them on const objects, which is what d1 and d2 are.

All methods that logically don't need to modify the object should be marked const.

answered Oct 09 '14 at 14:51

Luchian Grigore

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this seems to break my program :C – jonas rudzionis Oct 09 '14 at 14:54
Agree with @Luchian [this is worth a read](http://stackoverflow.com/questions/136880/sell-me-on-const-correctness). – Cory Kramer Oct 09 '14 at 14:55
@jonasrudzionis meaning? – Luchian Grigore Oct 09 '14 at 14:55
i start getting library errors, as in: 'bool std::operator <(const std::vector<_Ty,_Alloc> &,const std::vector<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::vector<_Ty,_Alloc> &' from 'Studentas' – jonas rudzionis Oct 09 '14 at 14:56
i've done the same thing with container class but vector just screws me with that sort – jonas rudzionis Oct 09 '14 at 14:58
@jonasrudzionis that's a different error, please post a new question with the new code (stripped down to the minimum that reproduces the new error) – Luchian Grigore Oct 09 '14 at 15:00
Hey, figured i'll just post here, the problems was that my overlayed opperator was edited in a way that was glitching out, I was just a little bit careless while writting.Your thing worked when implemented for some stuff later, thanks a lot. – jonas rudzionis Oct 09 '14 at 18:52

Using sort for a class vector with private variables

1 Answers1