Depth-first graph traversal

I'm trying to print a depth-first traversal. I have the following code which continues to give me a seg fault. It seems to be occurring when I try to print the last vertex in the graph. The first traversal I do starting at vertex 'A', works as it should. But when I try to do a depth-first print starting from D, I get the seg fault. Here is my source code: Here is my original source code: ``` void wdigraph::depth_first(int u) const { bool found = false; vector<bool> visited; // create a boolean vector for(int i =0; i < size; i++) // the size of the graph visited.push_back(false); // to mark when a node has been visited stack<int> depth_first; // used to hold vertices that have been visited visited[u] = true; // mark as visited cout << label[u]; // print first vertex depth_first.push(u); // put first vertex on stack while(!all_visited(visited)) { // continue until all vertices have been visited found = false; for(unsigned i = 0; i < visited.size() && !found; i++) { if(adj_matrix[u][i] != 0 && !visited[i]) { // found next vertex cout << "->" << label[i]; // print vertex visited[i] = true; // mark vertex as visited depth_first.push(i); // push vertx onto stack found = true; // set found = true to end for loop u = i; }//endif }//endfor if(found == false) { // no available neighbors u = depth_first.top(); // get top of stack depth_first.pop(); // pop from stack }//endif }//endwhile cout << '\n'; } void wdigraph::print_graph() const { cout << '\n'; cout << "No of Nodes = " << size << endl; cout << "\nAdjacency Matrix\n" << endl; cout << " |"; for(int i = 0; i < size; i++) cout << " " << label[i]; cout << '\n'; cout << "--|"; for(int i = 0; i < size; i++) cout << "---"; cout << '\n'; for(int i = 0; i < size; i++) { cout << label[i] << " |"; for(int j = 0; j < size; j++) { if(adj_matrix[i][j] != 0) cout << " " << setw(2) << right << adj_matrix[i][j]; else cout << " -"; }//endjfor cout << '\n'; if(i != size-1) cout << " |" << endl; }//endifor cout << '\n'; } bool all_visited(vector<bool> &v) { for(unsigned i = 0; i < v.size(); i++) if(v[i] == false) return false; return true; } ``` This is the header file and the constructor: ``` // definition of weighted digraph #define NO_NODES 1 // default size for no of nodes in digraph #define LINK_PROB 0.25 // prob of having direct link between nodes #define MAX_WEIGHT 10 // max weight factor for links class wdigraph { public: wdigraph ( int = NO_NODES ); // default constructor ~wdigraph ( ) { }; // destructor int get_size ( ) const { return size; } // returns size of digraph void depth_first ( int ) const;// traverses graph using depth-first search void print_graph ( ) const; // prints adjacency matrix of digraph private: int size; // size of digraph vector < char > label; // node labels vector < vector < int > > adj_matrix; // adjacency matrix }; // default class constructor wdigraph :: wdigraph ( int n ) : size ( n ) { // allocate dynamic memory label = vector < char > ( size ); adj_matrix = vector < vector < int > > ( size ); for ( int i = 0; i < size; i++ ) adj_matrix [ i ] = vector < int > ( size ); // assign labels to each node label [ 0 ] = 'A'; for ( int i = 1; i < size; i++ ) label [ i ] = label [ i - 1 ] + 1; // determine weights for links between nodes randomly // and build adjacency matrix srand ( 1 ); for ( int i = 0; i < size; i++ ) { adj_matrix [ i ] [ i ] = 0; bool flag = false; for ( int j = 0; j < size; j++ ) { if ( j == i ) continue; double r = ( double ) rand ( ) / RAND_MAX; adj_matrix [ i ] [ j ] = ( r <= LINK_PROB ) ? rand ( ) % MAX_WEIGHT + 1 : 0; if ( adj_matrix [ i ] [ j ] > 0 ) flag = true; } // if node is not connected to any other node, then // connect this node to random node if ( size > 1 && !flag ) { int k; while ( ( k = rand ( ) % size ) == i ) ; adj_matrix [ i ] [ k ] = rand ( ) % MAX_WEIGHT + 1; } } } ``` Here is the main routine: ``` #define M 3 // print every M-th node's path when traversing #define N2 5 // number of nodes in second graph #define N3 20 // number of nodes in third graph void proc_graph(wdigraph&); // function declaration int main() { // create three weighted digraphs wdigraph graph1(NO_NODES); wdigraph graph2(N2); wdigraph graph3(N3); //proc_graph(graph1); // print first graph proc_graph(graph2); // print first graph //proc_graph(graph3); // print first graph return 0; } void proc_graph(wdigraph &g) { cout << '\n'; cout << "A Weighted Digraph" << endl; // print header cout << "__________________" << endl; // print header underline g.print_graph(); // print graph cout << "Paths by Depth-First Search" << endl; for(int i = 0; i < g.get_size(); i += M) g.depth_first(i); } ``` This is the output that I am getting. The graph shows the weight of each edge. A '-' means there is no edge. ``` A Weighted Digraph __________________ No of Nodes = 5 Adjacency Matrix | A B C D E --|--------------- A | - - - 6 - | B | - - 8 - - | C | 7 - - - - | D | 7 9 10 - 1 | E | 4 - 10 - - Paths by Depth-First Search A->D->B->C->E Segmentation fault (core dumped) ``` If I remove the `u = i` code from the for loop, then my program works fine. Here is my output when I try to print the third graph. Notice, my traversal is not traveling correctly.