CODEWITHSUNDEEP
c++stdmap
dev_nut
dev_nut

Reputation: 2542

How do I cleanly pass a std::map between two objects?

I'm having a factory method object that creates a map as follows:

// std namespace is imported

Foo* createFoo() {
   map<int,int>* fooMap = new map<int,int>();
   for (int i=0;i < 4;i++) {
      fooMap->insert(make_pair(i+1, i+2));
   }
   return new Foo(fooMap);
}

The foo class is as follows:

class Foo { 
    private: 
        map<int,int>* m_fooMap; 
    public: 
        Foo(map<int,int>* fooMap) : m_fooMap(fooMap) { }; 
        void doIt() {
            cout << m_fooMap->at(1) << endl;
        }
}

This seems to throw an exception if I call the doIt function. When I debugged I noticed that the map object seems to not get created and populated. How can I correctly create a map on the heap?

PS: I don't want to create the map and pass by value, I'd prefer to do it through a pointer as a learning exercise. Also, if I create the map on the stack it gets populated, but of course I can't pass it to the Foo objects since it goes out of scope.

Upvotes: 0

Views: 224

Answers (1)

juanchopanza
juanchopanza

Reputation: 227390

I would favour an approach without any explicit dynamic memory allocation:

class Foo { 
    private: 
        std::map<int,int> m_fooMap; 
    public: 
        Foo(const std::map<int,int>& fooMap) : m_fooMap(fooMap) {}; 
        Foo(std::map<int,int>&& fooMap) : m_fooMap(std::move(fooMap)) {}; 
        void doIt() {
            cout << m_fooMap.at(1) << endl;
        }
};

Foo createFoo() 
{
   std::map<int,int> fooMap;
   for (int i=0;i < 4;i++) {
      fooMap.insert(make_pair(i+1, i+2));
   }
   return Foo(fooMap);
}

Upvotes: 1

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