CODEWITHSUNDEEP
c++
tariq zafar
tariq zafar

Reputation: 659

Direct constructor call in C++

I have a function and a class as below

class Vertex {
public:
    int mId;
public:
    Vertex(int info=-1) : mId(info) {

    }
};

class Edge {
public:
    Vertex mStart, mEnd;
    int mWeight;
public:
    Edge(Vertex start=-1, Vertex end=-1, int wt=-1) :
        mStart(start), mEnd(end), mWeight(wt) {
    }
};

class Graph {
    void addEdge(const Edge& e) {
        //Adds this edge to a vector
    }
};

shared_ptr<Graph> mygraph(new Graph(13 //no of vertices
                             , 17   //no of edges
                             , false));

mygraph->addEdge(Edge( 1, 2, 1));
mygraph->addEdge(Edge( 3, 1, 1));
mygraph->addEdge(Edge( 1, 6, 2));
mygraph->addEdge(Edge( 1, 7, 4));
...

Here I am passing direct Edge values in a constructor and get no crash. But I guess there will be a memory leak here. Whats the correct way to pass an object by reference after doing construction?

PS: Assume that Vertex is an implicit constructor accepting int as id.

Upvotes: 1

Views: 337

Answers (1)

mexus
mexus

Reputation: 1170

There wouldn't be any memory leaks, destructors will be automatically called, as @Borgleader wrote

You didn't use new for the edges -> no memory leak If you don't name objects it doesn't mean they wouldn't be destroyed. Everything's okay.

Although you can perform a little optimisation if you are using C++11. In your code object Edge is created, then passed by a const reference to a function addEdge(), where it will be copied to a vector with a copy constructor. You can avoid this overhead by using std::vector::emplace_back! And templates. Like so:

class Graph {
    public:
    template<class... Args>
    void addEdge(Args&& ...args) {
        //Assuming vector is std::vector<Edge>
        vector.emplace_back(args...);
    }
};
mygraph->addEdge(1, 2, 1);

Of course all created objects will be automatically destroyed when vector is cleared.

And, BTW, if you ever doubt whethere your program has memory leaks, Valgrind is at your service!

Update:

I've coded a tiny and simple example showing the difference, see it at http://ideone.com/ARzhL2. You can scroll directrly to a stdout section to see the result.

Upvotes: 3

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