EXC_BAD_ACCESS pointer C++ - c++

Question

This is by far the most frustrating error I have come across while programming in C++. Here is the code I am trying to run. Every time I run it, it gives me bad access error and when I try to debug it with LLDB, it shows that value of every member in end = 0 and gives the bad access pointer error. Please let me know what's the solution to the current problem. I have been stuck on this for a while now and I come across this error every now and then so any debugging tips would be appreciated.
struct edge;
struct node
{
int id;
double longitude;
double latitude;
double distance;
string state;
string name;
vector<edge*>r;
int prio;
};
struct edge
{
string name, type;
double dist;
node* x;
node* y;
void print()
{
cout << name << " " << type << " "<< dist << " miles" << " from " << x->id << " to " << y->id << endl;
}
edge(node* x, node* y, double dist, string name)
{
this->x = x;
this->y = y;
this->dist = dist;
this->name = name;
}
edge(){};
};
struct route{
int place1;
int place2;
string rt;
string vert;
double lengt;
route(int o, int d, double l,string r ){
place1 = o;
place2 = d;
rt =r;
lengt=l;
}
};
struct compPair
{
bool operator()(node* a, node* b)
{
return a->prio > b->prio;
}
};
void SPT(vector<node*> & g, int from, int to){
priority_queue <node *, vector<node*>, compPair> pq;
g[from]->prio = 0;
pq.push(g[from]);
while(!pq.empty()){
node* place1 = pq.top();pq.pop();
for(int i=0;i<place1->r.size();i++){
edge* rd = place1->r[i];
node* place2 = rd->x;
if(place2==place1){
place2=rd->y;
}
if(place2->prio == -2){
place2->prio = place1->prio + rd->dist;
pq.push(place2);
}
else if (place2->prio > (place1->prio + rd->dist)){
place2->prio = place1->prio + rd->dist;
}
}
}
node* beg = g[from];
node* end = g[to];
if(g[from]->prio < 0 || g[to]->prio < 0){
cout <<"Path does not exist";
return;
}
//THIS IS BUGGY CODE, everything works fine without this code //
node* lowp = end;
vector <route*> p;
while(beg!=end){
double reallowp = end->prio;
edge* rtt = end->r[0];
for(int i =0;i<end->r.size();i++){
edge *r = end->r[i];
node* town1 = r->x;
if(town1 == end){
town1 = r->y;
}
if(town1->prio <= reallowp){
reallowp = town1->prio;
lowp = town1;
rtt = r;
}
}
route* e = new route(end->id,lowp->id,rtt->dist,rtt->name);
p.push_back(e);
end=lowp;
}
for(int i=p.size()-1;i>=0;i--){
cout << "From intersection " << p[i]->place2 << "take " << p[i]->rt << " " << p[i]->lengt << " miles to intersection " << p[i]->place1 << endl;
}
}
int main()
{
vector<node*>t = readTown();
readRoad(t);
SPT(t,68,69);
}