Question

The relevant (I think) lines of my coding are below.
What is meant is that there is a list of Clusters.
One of them, base, will absorb another one (the aborbed).
The aborbed cluster should be erased from the list.

First problem I encountered was that I needed to perform other operations in both base and absorbed clusters, after while cycle closes.
From my searches, I found the = &(*li) stuff. What I understand is that I get a pointer to the address of the element li points to, although I cannot do absorbed = li, because one is an iterator and the other a (simple?) ponter. I’d appreciate some explanation on this.

Now, the bigger problem is that I get a sementation fault in the line c->getPoints(); of the method joinCluster()
What am I doing wrong? What should I do an why?

I’m using g++ (GCC) 4.5.2 in Linux x86_64.

Cluster * base;
Cluster * absorbed;

list<Cluster>::iterator li = clusters.begin(); 
while ( li != clusters.end() ) {   
    if (li->getId() == p2) {
        absorbed = &(*li);
        li = clusters.erase(li);
    } else if (li->getId() == p1) { 
        base = &(*li);
    }
++li;
}

base->joinCluster(absorbed);


void Cluster::joinCluster(Cluster * c)
{
    set<unsigned int> pts = c->getPoints(); 
}

set<unsigned int> Cluster::getPoints()
{
return points;
}

class Cluster {
    private:
    std::set<unsigned int> points;
    public:
    std::set<unsigned int> getPoints();
};

Answer 1

list<Cluster>::iterator li = clusters.begin(); 
while ( li != clusters.end() ) {   
    if (li->getId() == p2) {
        absorbed = &(*li);
        li = clusters.erase(li);
    } else if (li->getId() == p1) { 
        base = &(*li);
    }
++li;   // <----  Don't increment when you already deleted.
}

When you delete then last element in the list, li becomes cluster.end(). Then you increment it again and boom, you’re out of bounds. ++li should go in else block.

Note also, when you erase li from the container, absorbed holds an invalid adress.