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I'm trying to implement a Graph class with shared_ptr. I've declared my class as below.

class Graph
{
    public:
        Graph(int V);
        Graph()=delete;
        void AddEdge(int src, int dest);
        void BFS(int s);
        ~Graph();
    private:
        int V;
        std::shared_ptr<std::list<int>[]> adj;
};

When I try to initialize my adjList like below in the constructor, I'm getting a compilation error.

Graph::Graph(int V)
{
    this->V = V;
    adj = std::make_shared<std::list<int>[]>(new std::list<int>[V]);
}

Error:

/usr/include/c++/9/bits/shared_ptr.h:717:39:   required from ‘std::shared_ptr<_Tp> std::make_shared(_Args&& ...) [with _Tp = std::__cxx11::list<int> []; _Args = {std::__cxx11::list<int, std::allocator<int> >*}]’
Graph.cpp:21:67:   required from here
/usr/include/c++/9/ext/new_allocator.h:145:20: error: no matching function for call to ‘std::__cxx11::list<int>::list(std::__cxx11::list<int>*)’

What am I doing wrong ?

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2
  • Rethink your approach. Why to you want a std::shared_ptr to an array of std::list? Consider using a std::vector of std::lists as a replacement. Commented Oct 30, 2020 at 16:44
  • 1
    C++11 has only one make_shared function. Commented Oct 30, 2020 at 16:45

1 Answer 1

Reset to default
2

C++11 has only one make_shared function. This is what its prototype looks like:

template< class T, class... Args >
shared_ptr<T> make_shared( Args&&... args );
  1. T can't be an array.
  2. The function accepts arguments that will be passed to the T constructor, but std::list has no constructor that can accept new std::list<int>[V].
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