stl set insert problem

[damxam]

Hello all,
thanks in advance for the help.

I'm trying to get back into C++ programming after a few years mainly programming java. I thought I'd try to implement a simple graph to get me started.

The code:

/*
 * Main.cpp
 *
 *  Created on: 19/10/2012
 */
#include <iostream>
#include <set>
#include <map>
#include <stdio.h>
#include <stdlib.h>
#include <vector>

using namespace std;


class Node
{
private:
	int id;
	string name;
	set <Node*> adjacents;
	bool visited;
//	static int b ;
//	static set <int> allids;
public:
	Node(string str)
	{
		id = -1;
		visited = false;
		name = str;
		adjacents = set <Node*>();
//		b = 4;
	}

	void addAdjacent(Node * n)
	{
		adjacents.insert(n);
	}

	string getName()
	{
		return name;
	}

	int getId()
	{
		return id;
	}

	void setId(int _id)
	{
//		if(allids.find(_id) != allids.end())
//		{
//			cout << "Error, already have id " + _id << endl;
//			exit(-1);
//		}
		id = _id;
	}

	set <Node*> getAdjacents()
	{
		return adjacents;
	}

	void print(string indent)
	{
		cout << indent << id << ": ";
		set<Node*>::iterator it = adjacents.begin();
		while(it != adjacents.end())
		{
			cout << "(" << (*it)->getId() << ", " << (*it)->getName() << ")" << ", ";
			it++;
		}
		cout << endl;
	}

	void setVisited(bool v)
	{
		visited = v;
	}

	bool isVisited()
	{
		return visited;
	}
};
//static int b = 0;
//const set <int> Node::allids;

//const set <int> Node::allids;

class Graph
{
public:
	Graph()
	{
		//root = new Node("root");
		nodes = new map <int, Node*>();
		allNodes = set <Node*>();
		idAt = 0;
	}

	void initGraph(vector <pair <int, int> > _nodes)
	{
		cout << "ig" << 1 << endl;
		bool first = false;
		//Node * firstNode;

		for(int i = 0; i < _nodes.size(); i++)
		{
			cout << "ig" << 2 << endl;
			pair <int, int> p = _nodes[i];
			if((*nodes)[p.first] == NULL)
			{
				cout << "Creating" << endl;
				createNode("Node", p.first);
				cout << "Created" << endl;
			}
			else
			{
				cout << "Not creating, " << (*nodes)[p.first] << " != " << NULL << endl;
			}
			if((*nodes)[p.second] == NULL)
			{
				createNode("Node", p.second);
			}
			if((*nodes)[p.first] == NULL || (*nodes)[p.second] == NULL)
			{
				cout << "Error, node creation unsuccessful" << endl;
				exit(-1);
			}
			cout << "Trying to link" << endl;
			createLink((*nodes)[p.first], (*nodes)[p.second]);
			cout << "Linked" << endl;
			if(!first)
			{
				first = true;
//				createLink(root, nodes[p.first]);
				root = (*nodes)[p.first];
			}
			cout << "ig" << 3 << endl;
		}
		cout << "ig" << 4 << endl;
	}

	void createLink(Node * n1, Node * n2)
	{
		n1->addAdjacent(n2);
	}

	Node * createNode(string name, int id)
	{
		cout << "Name is " << name << endl;
		Node * n = new Node(name);
		cout << "Now Name is " << n->getName() << endl;
		n->setId(id);
		if((*nodes)[id] != NULL)
		{
			cout << "Error, nodes[" << id << "] not nodes.end()";
			exit(-1);
		}
		//nodes->insert(pair <int, Node*> (id, n));
		//nodes.insert(make_pair(id, n));
		pair <map <int, Node*>::iterator, bool> result = nodes->insert(make_pair(id, n));
		cout << "Status = " << result.second << endl;
		cout << "Iterator = " << result.first->first << flush;
		cout << ", " << result.first->second->getId() << endl;
		//(*nodes)[id] = n;
		cout << "Max size " << nodes->max_size() << endl;
		//make_pair(id, n);
		if((*nodes)[id] == NULL)
		{
			cout << "Should NOT be null" << endl;
			cout << "Size is " << nodes->size() << endl;
			map <int, Node*>::iterator it = nodes->begin();
			cout << "Looking for " + id << endl;
			cout << "Nodes present:" << endl;
			while(it != nodes->end())
			{
				cout << (*it).first << ", " << (*it).second->getId() << endl;
				it++;
			}
			exit(-1);
		}
		//nodes[id] = n;
		allNodes.insert(n);
		return n;
	}

	/*
	void addNode(Node * n)
	{
		int id = idAt++;
		n->setId(id);
		nodes->insert(pair <const int, Node*> (id, n));
		allNodes.insert(n);
	}*/

	Node * getRoot()
	{
		return root;
	}

	void printGraphHelper(Node * n, string indent)
	{
	//	cout << "Visiting " << n->getId() << endl;
		n->print(indent);
		n->setVisited(true);
		indent += "  ";
		set <Node*> adjacents = n->getAdjacents();
		set<Node*>::iterator it = adjacents.begin();
		while(it != adjacents.end())
		{
			//cout << "At " << !(*it)
			if(!(*it)->isVisited())
			{
				printGraphHelper((*it), indent);
			}
			it++;
		}
	}

	void printGraph()
	{
		clearAllFlags();
		printGraphHelper(root, "");
	}

	void clearAllFlags()
	{
		set<Node*>::iterator it = allNodes.begin();
		while(it != allNodes.end())
		{
			(*it)->setVisited(false);
			it++;
		}
	}

private:
	Node * root;
	set <Node*> allNodes;
	map <int, Node*> *nodes;
	int idAt;// = 0;
};

int main ()
{
	Graph * g = new Graph();
	vector <pair <int, int> > v = vector <pair <int, int> >();
	v.push_back(pair <int, int> (0,1));
	v.push_back(pair <int, int> (1,2));
	v.push_back(pair <int, int> (1,3));
	v.push_back(pair <int, int> (1,4));
	v.push_back(pair <int, int> (3,4));
	v.push_back(pair <int, int> (4,5));
	v.push_back(pair <int, int> (2,5));
	v.push_back(pair <int, int> (5,1));
	g->initGraph(v);
	cout << "GraphInit" << endl;
	g->printGraph();
	return 0;
}

The problem is in the createNode() function in the graph class when I try to insert the node into the nodes map that keeps track of all my nodes by id.
If I use this way of inserting into the map (currently commented out):
(*nodes)[id] = n;
everything works fine.

However, if I use this way:
pair <map <int, Node*>::iterator, bool> result = nodes->insert(make_pair(id, n));
which as far as I understand should be equivalent, then the if conditional if((*nodes)[id] == NULL) fires and the program crashes (segmentation fault) when I try to use the iterator to print out all the values in the nodes map.
When I use the gdb debugger, if if remove the cout lines right after the insert then it shows me the application crashes when trying to call the getId() method in the second line of this loop:

while(it != nodes->end())
{
        cout << (*it).first << ", " << (*it).second->getId() << endl;
	it++;
}

I also notice that the return value from the insert call is 'false' for result.second, indicating that the value was not successfully inserted.

I am using Eclipse and the mingw g++ compiler.

I'm probably doing something really silly so apologies in advance but I just can't seem to figure it out.

Thanks again!

[Zhuge]

If you've used the [] operator as nodes[id] at any point before you do the insert, I'm fairly certain that creates an uninitialized value at 'id'. So any insert call afterward would fail as there is already a value where you are trying to insert.

[damxam]

Hey Zhuge,
that's it!

I replaced the nodes[id] == NULL with nodes.find(id) == nodes.end() and now it works like a charm.

Thanks, it was driving me nuts.

[Zhuge]

Glad I could help.