Question

The folowing code is giving a segfault when reaching the insert statement:

rna* annealer::anneal(rna strand1, rna strand2, const rna & opponent){

 std::vector<nukleotid*>::iterator sit2;
 std::vector<nukleotid*>::iterator eit2;
 std::vector<nukleotid*>::iterator eit;

 if(tryAnneal(strand1, strand2, opponent)) {
  eit = strand1.getStrand().end();
  sit2 = strand2.getStrand().begin();
  eit2 = strand2.getStrand().end();

         //here be segfault
  strand1.getStrand().insert(eit, sit2, eit2);
  strand1.isAnnealed = true;
  rna* str = &strand1;
  std::cout << *str << std::endl;
  return str;
 }


    //...

 return NULL;
}

rna contains a vector, which is returned by getStrand().

Its driving me crazy. I really cant understand why theres a segfault. A slightly different version of the code, in which in didnt declare new iterators, but was just passing strand1.getStrand().end(); (and the two other), to vector::insert() derictly threw a length_error which does not make any sense either, as my vectors are small (~10 elements).

can anyone see what am i doing wrong here?`

Answer 1

If getStrand() returns a vector by value, then sit2 and eit2 are iterators into different copies of the vector, and both copies are destroyed as soon as you obtain the iterators. You need either to return the vector by reference or save the copy of the vector and obtain iterators from that one copy instead.