Question

I have a std::set and I need to erase similar adjacent elements:

DnaSet::const_iterator next = dna_list.begin();
DnaSet::const_iterator actual = next;
++next;

while(next != dna_list.end()) // cycle over pairs, dna_list is the set
{
    if (similar(*actual, *next))
    {
        Dna dna_temp(*actual);  // copy constructor
        dna_list.erase(actual); // erase the old one
        do
        {
           dna_temp.mutate(); // change dna_temp
        } while(!dna_list.insert(dna_temp).second);  // insert dna_temp
    }
    ++actual;
    ++next;
}

Sometimes the program can’t exit from the main loop. I think the problem happens when I erase the last element in the dna_list. What’s the correct way to do this task?

Answer 1

Use actual = next rather than ++actual.

Once you erase actual, it is an invalid iterator, so ++actual will behave strangely. next should remain intact, so assigning actual to next should work.