c++ has stopped working static map function

Question

I've created two classes: package and tourpackage that inherits the package class. The tour package class contains a vector of destinations. I've created a package vector and now I want for each destination in the vector to display the number of appearances. I've created a static map and a static function that returns the map so I can access it from the main functions. But when I try to display the map, the program displays but then says it has stopped working. If I make the map public then it works, but I want it to be private

TourPackage.h:

#ifndef TourPackage_H
#define TourPackage_H
#include "Package.h"
#include <vector>
#include <string>
#include <iostream>
#include <map>
using namespace std;
class TourPackage: public Package
{vector <string> destinations;
int lenght;
static map <string, int> frequency;
    public:

        TourPackage(double, int lenght);
        virtual ~TourPackage();

    static map <string, int> frequencies ()
    {
        return frequency;
    }

    protected:

    private:
};

#endif

TourPackage.cpp:

#include "TourPackage.h"
TourPackage::TourPackage(double price,int n):Package (price)

    {
    string aux;
    int max1=0;
        lenght=n;
        string x;
        for (int i=0;i<lenght;i++)
        {getline (cin, x);
        destinations.push_back(x);

        ++frequency[destinations[i]];}



    }

    TourPackage::~TourPackage()
    {
        //dtor
    }

main.cpp

#include <iostream>
#include <vector>
#include <string>
#include "TourPackage.h"
#include <typeinfo>
#include <map>
#include <utility>
#include <algorithm>

using namespace std;
map <string, int> TourPackage::frequency;
bool comp (const pair <string, int> &l, const pair <string, int> &r)
{
    if (l.second!=r.second)
        return l.second>r.second;
    return l.first>r.first;
}
int main()
{TourPackage p(2,4);

vector <Package*> Packages;
    Packages.push_back (new Package (1000));
    Packages.push_back (new Package (4234));
    Packages.push_back (new TourPackage (32,3));
    Packages.push_back (new TourPackage (234, 4));
    Packages.push_back(new TourPackage (43, 5));

for (map <string, int>::const_iterator is=TourPackage::frequencies().begin(); is!=TourPackage::frequencies().end();is++)
    cout<<is->first<<" "<<is->second<<" ";
cout<<endl;





cout<<endl;
return 0;

}

Some programmer dude · Accepted Answer · 2018-05-27 14:49:38Z

2

You have declared the frequencies function like:

static map <string, int> frequencies ()

That is, it returns the map by value.

Which means

is=TourPackage::frequencies().begin();

and

is!=TourPackage::frequencies().end()

where each call returns a different object. The iterators from the different maps can not be compared to each other, attempting to do so will lead to undefined behavior.

Change the frequencies function to return a reference:

static map <string, int>& frequencies ()
//                      ^
//  Returning a reference

edited May 27, 2018 at 14:49

answered May 27, 2018 at 14:46

Some programmer dude

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1 Comment

JVApen Over a year ago

Maybe the return value also needs to be const? Depending on whether it is possible to change the map as external user.

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