allocating space to list pointers using malloc not working

Question

class graph
{

    int v;
    list *adj;
    void dfsutil(int v,bool visited []);
    public:
    graph(int v)
    {
        this->v=v;
        //adj =         


        

Answer 1

You did not create an array of std::list objects when you used malloc. All malloc does is allocate memory from the heap -- no objects are created. Thus attempting to use your std::list's as if they are created correctly will result in undefined behavior.

You should use a container such as std::vector to store your list objects:

#include <vector>
#include <list>

class graph
{
    int v;
    std::vector<std::list<int>> adj;
    void dfsutil(int v,bool visited []);
    public:
        graph(int num) : v(num), adj(num) {}
    void addedge(int v,int w);
    void dfs(int v);
};

Note there is no need to allocate memory. The rest of your code should stay the same, since vector has an overloaded operator [] to access the items.