asked on 9/4/2013

Can't add custom objects to a set

I have a custom class named videoType. I'm trying to add several videoType objects to a set named videoSet like this:

set<videoType> videoSet;

videoType video1("Titanic", 1);
videoType video2("Star Wars", 2);

videoSet.insert(video1);

When I try to add video1 to the set, I get an error message that points to this line of code in the stl_functions.h file:

/// One of the @link comparison_functors comparison functors@endlink.
template<typename _Tp>
struct less : public binary_function<_Tp, _Tp, bool>
{
bool
operator()(const _Tp& __x, const _Tp& __y) const
{ return __x < __y; }
};

I overloaded all the comparison operators in the videoType class so that the videoType objects can be sorted. Is there something else I need to do to enable the objects to be inserted into the set?

Attached are my files.
videoType.h
main.cpp

Programming Languages-Other C++

Last Comment

MBarongan

9/4/2013

MBarongan

9/4/2013

ASKER

The attched videoType.h file has an error in the function that overloads the > operator:

bool videoType::operator>(videoType otherVideo)
{
return (ID < otherVideo.ID);
}

I just corrected (ID < otherVideo.ID) to (ID > otherVideo.ID), but this did not resolve the issue.

SOLUTION

Zoppo

9/4/2013

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ASKER CERTIFIED SOLUTION

phoffric

9/4/2013

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phoffric

9/4/2013

I focused on less (<) rather than > because set, by default compares using less.
http://www.cplusplus.com/reference/set/set/

phoffric

9/4/2013

An alternative to your defining operator<() is to define a functor comparator that you associate with your set constructor. See, for example, how struct classcomp is used in the following link:
http://www.cplusplus.com/reference/set/set/set/

// constructing sets
#include <iostream>
#include <set>

bool fncomp (int lhs, int rhs) {return lhs<rhs;}

struct classcomp {
  bool operator() (const int& lhs, const int& rhs) const
  {return lhs<rhs;}
};

int main ()
{
  std::set<int> first;                           // empty set of ints

  int myints[]= {10,20,30,40,50};
  std::set<int> second (myints,myints+5);        // range

  std::set<int> third (second);                  // a copy of second

  std::set<int> fourth (second.begin(), second.end());  // iterator ctor.

  std::set<int,classcomp> fifth;                 // class as Compare

  bool(*fn_pt)(int,int) = fncomp;
  std::set<int,bool(*)(int,int)> sixth (fn_pt);  // function pointer as Compare

  return 0;
}

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MBarongan

9/4/2013

ASKER

Thank you Zoppo and phoffric. Adding const and the '&' symbol fixed the problem.