When to use break inside a forloop

[sheva29]

I'm having a hard time grasping the use of break inside a loop. I know that in switch cases, the objective to tell the compiler to not get into that case.

Now in forloops I thought it was to tell the compiler to break the loop and go back out. I came up with a problem that was solved by using the break at the end of a for loop here is the code:

if( familyButton->isLoadingCompleted == true){// once we have finished the loader in our button. we reset some values
                
  attractorCounter = 6;// switch our counter back to 4.
  families->changeBoidStateToZero();// this function switches the boidState to 0 and makes sure the particles go back to screen.
                
  //we also send the notes that are being selected
  if ( bottle->bottleLabels.size() > 0 ){// we check if the size of the vector is 0
   //vvvvvvvvvvvvvvvvvvvvvvvvvvvvv This was making the compiler crash
   vector<BottleButtonLabel>::iterator it;
   for (it = bottle->bottleLabels.begin(); it != bottle->bottleLabels.end(); it++){
          
     it = bottle->bottleLabels.erase(it);
     break;// this fixed the compiler from crashing.
   }
  }
 //^^^^^^^^^^^^^^^^^^^^^^^^^^^ This was making the compiler crash           
 if (families->returnFamilySelected() != -1) {
    int i = families->returnFamilySelected();
    for (int j = 0; j <  notes[i]->boidList.size();  j++){
      if (notes[i]->boidList[j]->boidState != 0){
         notes[i]->boidList[j]->boidState = 0;
      }
     }
    }
    familyButton->isLoadingCompleted == false;// and switch the main condition back to false so we don't go back here.
}

Is there any reason why in that particular part of the code, it avoided the compiler from crashing? I thought the if statement that was checking for the size of the vector will do the house keeping and tell the compiler to not go once an element was deleted.

I will appreciate some clarification on the concept.

[coder777]

on line 12: if you erase the last element (without break) the next thing happens (on line 10): it++. This mean you're beyond bottle->bottleLabels.end() and it != bottle->bottleLabels.end() cannot apply anymore. So it's likely that you erase elements that are not in the vector -> crash.

The loop on line 10 doesn't make sense with the break. It erases only the first element not more. To erase them all call clear():

http://www.cplusplus.com/reference/vector/vector/clear/

or if you want to do something before the element is erased:

   vector<BottleButtonLabel>::iterator it = bottle->bottleLabels.begin();
while(!bottle->bottleLabels.empty())
{
...
     it = bottle->bottleLabels.erase(it);
}

which is not very vector friendly

[mutexe]

http://stackoverflow.com/questions/4645705/vector-erase-iterator
http://stackoverflow.com/questions/8276901/vector-erase-iterator-out-of-range-in-c

break stops your iterations which stops the crash, but it will also stop you iterating over the complete vector.

[sheva29]

Makes lots of sense.

Thanks!