向量迭代器在C ++中不兼容

Question

I am trying to do a graph with 9 cities directly connected. I am having this problem with the function "shortpath". I keep getting an error "vector iterators incompatible" and I can't figure it out. Any help please. Thanks

This is the function:

void City::shortPath( vector<City*> & cities )
{
queue<City*> q;
q.push(this);

for( unsigned int i = 0; i < cities.size(); i++ )
{
    cities[i]->cityDistance = -1;
    cities[i]->visited1 = false;

}

q.front()->visited1 = true;

q.front()->cityDistance = 0;

while( !q.empty() )
{
    City * v = q.front();

    if( v->neighbor1.size() != 0 )
    {

        for( unsigned int i = 0; i < v->neighbor1.size(); i++ )
        {
            City * z = v->neighbor1[i];
            q.push( z );
            if( z->visited1 == false )
            {
            v->neighbor1[i]->cityDistance = v->cityDistance + 1; 
                v->neighbor1[i]->previous1.push_back( *v );
                v->neighbor1[i]->visited1 = true;
            }
        }


    }

    q.pop();

}




}

And this is the main:

int main()
{


City * NewDelhi = &City( "New Delhi" );
City * HongKong = &City("Hong Kong");
City * Washington = &City("Washington");
City * Dublin = &City("Dublin");
City * Lisbon = &City("Lisbon");
City * Vienna = &City("Vienna");
City * Santiago = &City("Santiago");
City * RioDeJaneiro = &City("RioDeJaneiro");
City * Berlin = &City( "Berlin" );
City * NewYork = &City( "NewYork" );


vector<City*> vector1;

vector1.push_back(HongKong);
vector1.push_back(NewDelhi);
vector1.push_back(Washington);
vector1.push_back(Dublin);
vector1.push_back(Lisbon);
vector1.push_back(Vienna);
vector1.push_back(Santiago);
vector1.push_back(RioDeJaneiro);
vector1.push_back(Berlin);
vector1.push_back(NewYork);



(*HongKong).neighbor1.push_back( NewDelhi );
(*NewDelhi).neighbor1.push_back( Washington);
(*Washington).neighbor1.push_back( Dublin );
(*Dublin).neighbor1.push_back( Lisbon );
(*Lisbon).neighbor1.push_back( Vienna );
(*Vienna).neighbor1.push_back( Santiago );
(*Santiago).neighbor1.push_back( RioDeJaneiro );
(*RioDeJaneiro).neighbor1.push_back( Berlin );
(*Berlin).neighbor1.push_back( NewYork );
(*NewYork).neighbor1.push_back( HongKong );




(*NewYork).shortPath( vector1 );

Answer 1

As Zan Lynx mentioned up there... you're using bad pointers.

I did write a quick test and there is the output of g++

make a
g++     a.cpp   -o a
a.cpp: In function ‘int main()’:
a.cpp:15:35: error: taking address of temporary [-fpermissive]
make: *** [a] Error 1

As you can see, it tells me that taking the address of a temporary is bad. Not only that, it does not actually compile since that's an error. cl could definitively do better on that one!

My test code, just in case:

#include <iostream>

class City
{
public:
  City(const std::string& name) : name_(name) { std::cout << "Constructed" << std::endl; }
  ~City() { std::cout << "Destructed" << std::endl; }
private:
  const std::string name_;
};

int main()
{
  std::cout << "Started" << std::endl;
  City *SF = &City("San Francisco");
  char c;
  std::cin >> c;
}

Answer 2

This can happen when you try to use an iterator that belongs to another vector of the same type. At some point you may be making a copy of a vector but and you use iterators from the original vector with the new copy.

In this case the culprit is caused by returning a copy of a vector or by passing a copy of a vector to a function along with iterators that belong to the original. You will need to review your code and look at how the vector and iteratos are being passed around. Any where that a copy is made is a potential source of the problem.

Also, as Roy pointed out this can also happen if you hold an old iterator after performing a modification of certain containers. In the case of vector any time you add or remove an element the internal storage may need to be resized causing all iterators to become invalid. Any attempt to use those iterators causes undefined behavior and anything can happen.

Answer 3

normally it's because you have some actions changed the vector after you saved a iterator, eg insert/erase, the previously saved iterator is no longer validate.

check your code to see if that is the case.