Problem to acces a position in an list c++ - c++

Question

I'm implementing a function to insert a set of nodes in a set of routes. This function is described as follows:
void Repair_ChooseARouteAndAPositionRandomly (SOLUTION &sol, vector<int> &NodesPscine, vector<int>&RoutesPscine, DATA data, int max_slot){
while (NodesPscine.size() != 0) {
int aux;
int pairpos;
int pairRoute;
int pairNode;
list<VEHICLE>:: iterator irouteit;
vector<bool> RotaJaFoiSorteada = vector<bool>(sol.SetP.size(),false);
pairpos = rand() % NodesPscine.size();
pairNode = NodesPscine[pairpos];
pairRoute = RoutesPscine[pairpos];
bool sorteaDenovo = true;
while (sorteaDenovo == true) {
bool rotaJafoiSorteada = false;
while (rotaJafoiSorteada == false) {
aux = rand() % sol.SetP.size();
if (RotaJaFoiSorteada[aux] == false) {
irouteit = next(sol.SetP.begin(), aux);
rotaJafoiSorteada = true;
RotaJaFoiSorteada[aux] = true;
}
}
bool NoJaExisteNaRota = false;
list<int>:: iterator ii;
for (ii = irouteit->rotaVehicle.begin(); ii != irouteit->rotaVehicle.end(); ii++) {
if (pairNode == *ii) {
NoJaExisteNaRota = true;
break;
}
}
if (NoJaExisteNaRota == false) {
double melhorDur = 0;
list <int>::iterator melhorPos = irouteit->rotaVehicle.begin();
double NovaDur;
InsereNaPosicaoMaisBarata (irouteit->rotaVehicle, irouteit->type, pairNode, data, melhorDur, melhorPos);
NovaDur = irouteit->duracaoTotal + melhorDur;
if (NovaDur <= max_slot) {
irouteit->rotaVehicle.insert(melhorPos,pairNode);
irouteit->duracaoTotal = NovaDur;
int cont = 0;
list<int>::iterator itprim = irouteit->rotaVehicle.begin();
list<int>::iterator itseg;
irouteit->distanceTotal = 0;
while (cont < irouteit->rotaVehicle.size()-1) {
itseg = next(itprim, 1);
irouteit->distanceTotal += data.dist[*itprim][*itseg];
++itprim;
++cont;
}
sorteaDenovo = false;
NodesPscine.erase(NodesPscine.begin()+pairpos);
RoutesPscine.erase(RoutesPscine.begin()+pairpos);
} // if (NovaDur <= max_slot) {
} // if (NoJaExisteNaRota == false) {
} // while (sorteaDenovo == true) {
} // while (NodesPscine.size() != 0) {
}
I also describe another function and some structs that may be important to identify my mistake.
void InsereNaPosicaoMaisBarata (list<int> Rota, int vehicle, int no, DATA data, double &melhorDur, list <int>::iterator &melhorPos ) {
list <int>:: iterator itprim = Rota.begin();
list <int>:: iterator itseg;
int cont = 0;
melhorDur = 10000000000000000;
while (cont < (Rota.size()-1)) {
itseg = next(itprim, 1);
double aux = data.l[vehicle][*itprim][no] + data.l[vehicle][no][*itseg] - data.l[vehicle][*itprim][*itseg];
if (melhorDur > aux) {
melhorDur = aux;
melhorPos = itseg;
}
++itprim;
++cont;
}
}
struct VEHICLE {
int type;
int idx;
double custo;
double distanceTotal;
double duracaoTotal;
list<int> rotaVehicle;
};
struct SOLUTION {
list<VEHICLE> SetP;
};
Everything goes fine to insert the first pairNode randomly chosen. However, when a second pairNode is chosen, the program runs until the line just after calling the function InsereNaPosicaoMaisBarata. If I put any cout inside this function, it does not appear. I think the problem is in the line "irouteit->rotaVehicle.insert(melhorPos,pairNode);", because when I comment it, the code runs until the end.
If I have, for example, these routes:
route 1 { 4 2 1 3 4 }
route 2 { 3 2 4 3 }
route 3 { 4 2 1 3 4 }
route 4 {4 1 3 4 }
route 5 { 2 4 2 }
route 6 { 3 2 4 3 }
If we have the nodes to be inserted in any of these routes as NodesPscine = {3,2}. If node 3 is randomly chosen to be inserted in route 5, it works well.
After, node 4 is chosen to be inserted in route 4. Then, the program runs until the function InsereNaPosicaoMaisBarata and the error message appears:
*** Error in `./heuristica': malloc(): memory corruption (fast): 0x00000000035d0680 ***
I suppose the way I'm identifying the melhorPos is not okay. But I can't figure out what is wrong.

Answer 1

You did not post all of your code, but one obvious mistake is this:
InsereNaPosicaoMaisBarata (irouteit->rotaVehicle, // <-- This parameter
irouteit->type,
pairNode,
data,
melhorDur,
melhorPos);
Your function is declared as this:
void InsereNaPosicaoMaisBarata (list<int> Rota, // <-- passed by value
int vehicle,
int no,
DATA data,
double &melhorDur,
list <int>::iterator &melhorPos )
Then inside the function, you do this:
list <int>:: iterator itprim = Rota.begin(); // <-- This is a local std::list
list <int>:: iterator itseg;
//...
itseg = next(itprim, 1);
//...
melhorPos = itseg; // <-- This is now referencing a local std::list entry
On return, you then use the last parameter:
irouteit->rotaVehicle.insert(melhorPos,pairNode); // <-- Trouble
The problem with all of this is that the first parameter (Rota) is passed by value. That means the function InsereNaPosicaMaisBarata is working with a temporary std::list.
You then set melhorPos to point to an entry into the temporary list. The problem is that on return, Rota has been destroyed, and you now have an invalid iterator being used on the return.
The solution is to change the function to have the first parameter as a reference:
void InsereNaPosicaoMaisBarata (list<int>& Rota, // <-- passed by reference
int vehicle,
int no,
DATA data,
double &melhorDur,
list <int>::iterator &melhorPos )