c++ - Why doesn't my code work? -

i'm implementing simple dfs traversal directed graph:

#include <iostream> #include <vector> #include <climits> #include <utility> #include <deque> #include <queue> #include <algorithm> #include <iomanip> #include <list>  using namespace std;  enum class color_type {     black,     white,     gray };  struct vertex {     char label;     color_type color;     int start;     int finish;     vertex *parent;     vector<vertex> adjacents;      vertex(char label)         :label(label), start(0), finish(0), color(color_type::white) {     }      void add_neighbor(const vertex &v) {         adjacents.push_back(v);     } };  class digraph { private:     vector<vertex> vertices;         int count;  public:     digraph()          :count(0) {         vertex a('a');         vertex b('b');         vertex c('c');         add_edge(a, b);         add_edge(b, c);         add_edge(c, a);         vertices.push_back(a);         vertices.push_back(b);         vertices.push_back(c);         (int = 0; < vertices.size(); ++i) {             vertices[i].color = color_type::white;             vertices[i].parent = null;         }     }      void add_edge(vertex &u, vertex &v) {         u.add_neighbor(v);     }      void dfs() {         dfs_visit(vertices[0]);     }      void dfs_visit(vertex &u) {         count++;         u.start = count;         u.color = color_type::gray;         cout << "??? visit = " << u.label << endl;         cout << "# neighbors: " << u.adjacents.size() << '\n';         (int = 0; < u.adjacents.size(); ++i) {             if (u.adjacents[i].color == color_type::white) {                 cout << "visit neighbor of [" << u.label << "] is: " << u.adjacents[i].label << endl;                 u.adjacents[i].parent = &u;                 dfs_visit(u.adjacents[i]);             }          }         u.color = color_type::black;         count++;         u.finish = count;     }  public:     friend ostream& operator <<(ostream& o, const digraph &dg) {         (int = 0; < dg.vertices.size(); ++i) {             o << dg.vertices[i].label << ":\n";             o << "\t start  = " << dg.vertices[i].start << endl;             o << "\t finish = " << dg.vertices[i].finish << endl;         }         return o;     } };  int main() {     digraph dg;     dg.dfs();     cout << dg << endl;     return 0; } 

the problem call dfs_visit() stop after visit 2nd vertex. pass vertex u reference parameter of dfs_visit() function, somehow number of neighbor of vertex b becomes 0 odd.
seemed me vertices stored in vector vertices not same ones passed dfs_visit, don't see how case. i've been using java while , i'm rusty c++. shed me lights regarding issue?

edit

this closer you're looking for, using pointers neighbors. hope helps. difference by-pointer addressing of neighbors within primary vertex container, opposed copies being made in code.

note: add-construction sets node have "next" node in vertices collection neighbor, finishing last node getting first neighbor. seemed you're code trying accomplish.

#include <iostream> #include <vector> #include <climits> #include <utility> #include <deque> #include <queue> #include <algorithm> #include <iomanip> #include <list>  using namespace std;  enum class color_type {     black,     white,     gray };  struct vertex {     char label;     color_type color;     int start;     int finish;     vertex *parent;     vector<vertex*> adjacents;      vertex(char label)     :label(label), start(0), finish(0), color(color_type::white) {     }      void add_neighbor(vertex &v) {         adjacents.push_back(std::addressof(v));     } };  class digraph { private:     vector<vertex> vertices;     int count;  public:     digraph()     :count(0) {         vertices.push_back(vertex('a'));         vertices.push_back(vertex('b'));         vertices.push_back(vertex('c'));         (size_t i=0; i<vertices.size(); ++i)         {             vertices[i].color = color_type::white;             vertices[i].parent = null;             vertices[i].add_neighbor(vertices[(i+1)%vertices.size()]);         }     }      void dfs() {         dfs_visit(vertices[0]);     }      void dfs_visit(vertex &u) {         count++;         u.start = count;         u.color = color_type::gray;         cout << "??? visit = " << u.label << endl;         cout << "# neighbors: " << u.adjacents.size() << '\n';         (int = 0; < u.adjacents.size(); ++i) {             if (u.adjacents[i]->color == color_type::white) {                 cout << "visit neighbor of [" << u.label << "] is: " << u.adjacents[i]->label << endl;                 u.adjacents[i]->parent = &u;                 dfs_visit(*(u.adjacents[i]));             }         }         u.color = color_type::black;         count++;         u.finish = count;     }  public:     friend ostream& operator <<(ostream& o, const digraph &dg) {         (int = 0; < dg.vertices.size(); ++i) {             o << dg.vertices[i].label << ":\n";             o << "\t start  = " << dg.vertices[i].start << endl;             o << "\t finish = " << dg.vertices[i].finish << endl;         }         return o;     } };  int main() {     digraph dg;     dg.dfs();     cout << dg << endl;     return 0; } 

output

??? visit = # neighbors: 1 visit neighbor of [a] is: b ??? visit = b # neighbors: 1 visit neighbor of [b] is: c ??? visit = c # neighbors: 1 a:      start  = 1      finish = 6 b:      start  = 2      finish = 5 c:      start  = 3      finish = 4