Can't figure out this subtle error

Code:

struct node{
    string location;
    int gval;
    int fval;
    node *next;
};

Code:

        struct node *hp;
        for(int i = 0; i<graph.size();i++)
	{
		cout << graph[i].location <<"=="<<graph[0].location<<"?\n";
		if((graph[i].location).compare(start)==0)
		{ 
			index = i;
			break;
		}
	}
    cout<<"Found "<< graph[index].location;
    //make starting nodes
    hp = (struct node*)(malloc(sizeof(struct node)));
    hp->location = graph[index].location;

For some reason the cout produces output fine with the string value of graph[index].location but when I debug my program, it crashes right at

Code:

 hp->location = graph[index].location;

Also graph is defined as

Code:

vector<vertice> graph = initializeGraph();

Code:

struct Edge
{
    string destination;
    int weight;
};
struct vertice
{
    string location;
    vector<Edge> directions;
};

Graph is a vector of vertice. Also when I am in the debugger, and I try to track the value of graph[i].location in the for loop, I get

Code:

graph[i].location    CXX0058: Error: overloaded operator not found

Dam I think it might be something with my syntax because I changed

Code:

hp = (structnode*)(malloc(sizeof(structnode)));
hp->location = graph[index].location;

to

Code:

node head;    
head.location = graph[index].location;
    hp=&head;

and it gets through this part perfectly fine.

Can someone explain what's going on? I actually came from a C point of view and trying to use C++, and it seems I don't even have to malloc, is that right? What are some of the things I am misunderstanding because it seems like the '->' use is different in C++ than in C? :/

A couple of comments.

Code:

        struct node *hp;
        for(int i = 0; i<graph.size();i++)
	{
		cout << graph[i].location <<"=="<<graph[0].location<<"?\n";
		if((graph[i].location).compare(start)==0)
		{ 
			index = i;
			break;
		}
	}
    cout<<"Found "<< graph[index].location;
    //make starting nodes
    hp = (struct node*)(malloc(sizeof(struct node)));
    hp->location = graph[index].location;

1. What guarantees that something will always be found. Or put another way, what garbage is in index if nothing is found.

2. Don't use malloc in a C++ program, use new.
hp = new node;

It might be an idea to add a constructor as well, which will at least make sure you have some plausible data.

Code:

struct node{
    string location;
    int gval;
    int fval;
    node *next;
    node ( ) : next(0) {}
};

As mentioned by Salem you should be using new and not malloc here. The later does not construct the std::string data member location, it simply allocates sizeof(std::string) space for that member but does not actually build it. Using new will properly construct that piece of the struct. This is most certainly the reason for your crash.

If your struct did not contain any objects needing to be constructed then using malloc would be allowable here but you'd still want to prefer new instead.

Are you writing some sort of graph? In that case, you should probably look at smart pointers. Otherwise I have to question why you use new (or malloc) in the first place.