Confusion with array of pointers

Question

This may be a dumb question but I'm getting pretty desperate at this point.

I am attempting to create an array of pointers:

struct vertex
{
std::string id;
std::string name;
int networkID;
std::vector<adjVertex> friends;
bool visited;
};

struct hobbylist
{
std::string hobby;
std::vector<vertex*> list;
};

hobbylist * hobbies[HASHMAP_SIZE];



 int Graph::addUserToHobby(std::string hobby1, std::string id){
//cout << "Adding to hobby: " << hobby1 << " user: " << id << endl;
vertex *user = findVertex(id);
int collisions = 0;
// initial key is based on the first 2 characters of the hobby name
int key = (hobby1[0] + hobby1[1]) % HASHMAP_SIZE;
//cout << " initial hashmap key " << key << endl;
hobbylist *h = new hobbylist;
if(hobbies[key] == NULL){
h->hobby = hobby1;
h->list.push_back(user);
hobbies[key] = h;}
else if (hobbies[key]!=NULL){
    hobbies[key]->list.push_back(user);
    collisions++;}
return collisions;
}

I am getting a seg fault at the last line in the else statement in the addUserToHobby function when running the function the first time and I am confused why the function would go to the else statement when the array should be empty and therefore hobbies[key] should be null the first time the function is run? Upon further inspection the function will always enter the else statement, so the array values are never null?

Erix · Accepted Answer · 2016-12-02 04:19:26Z

1

Each location is the array is not set to null by default, it's just whatever trash was in there before you allocated it.

answered Dec 2, 2016 at 4:19

Erix

7,1053 gold badges40 silver badges63 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

andrew fay Over a year ago

What would the best way to go about this because of that?

Erix Over a year ago

@andrewfay after the array is first declared, you could walk the whole thing and set each index to null. You can shorthand this by writing hobbylist * hobbies[HASHMAP_SIZE] = {0}

andrew fay Over a year ago

actually just ended up figuring it out by setting every value to null in my initializer. THANK YOU!

Collectives™ on Stack Overflow

Confusion with array of pointers

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related