vector - insert object to set c++ -

i have following fucntion handle points (among set of points) type start_vertex:

void handlestartvertex(vertex vi) {      cout << "start vertex begins ######################################################################################" << endl;     cout << "handling start " << vi << vertextype[vi.type] <<  endl;     halfedge *ei = vi.incidentedge;     std :: vector<halfedge > :: iterator it,itprev;     cout << "origin of incident edge " << *(ei->origin) << endl;     //insert ei in tow , set helper vi     ei->sethelper(&vi);     tow.push_back(*ei);      cout << "content of tow in start_vertex" << endl;     for(it = tow.begin();it != tow.end();it++)         cout << "origin of edge " << *((*it).origin) << " helper "  << *((*it).helper) << endl;     cout << "start vertex stops ######################################################################################\n\n" << endl; } 

where tow :

vector<halfedge >  tow;   

problem when setting helper of edge , pushing vector tow,for edges present in tow, helper changes of edge being presently pushed. not understanding why happening? work around appreciated. here results can make question more clear.

---

start vertex begins ########################################################################### handling start (2,9) start_vertex origin of incident edge (2,9)

content of tow in start_vertex
origin of edge (6,12) helper (2,9)

origin of edge (9,11) helper (2,9)

origin of edge (2,9) helper (2,9)

start vertex stops ############################################################################

correct result should getting is:
origin of edge (6,12) helper (6,12)

origin of edge (9,11) helper (9,11)

origin of edge (2,9) helper (2,9)

the vertex vi destroyed @ return of function. setting helper memory occupied vertex vi, , memory occupied vertex (2, 9) when last print. pass pointer vertex vi input function:

void handlestartvertex(vertex* vi) { ... }