C++ vector iterator: a foolish amateur mistake by me

I write this so other people won’t make the same mistake like me.. well no, just to babble about my bad day.

I wrote a code and tried to debug hours without result, my program keeps crashing. I thought my algorithm was wrong somewhere, division by zero have been handled and all. And it turns out the problem was because I foolishly push_back a vector while iterating it using iterator.

std::vector<SomeClass>::iterator i;
for (i=v.begin(); i<v.end(); i++){
  .....
  //in some cases, I have to do this
  v.push_back(SomeClass());
}

After reading c++ reference about push_back I just realized that “Reallocations invalidate all previously obtained iterators, references and pointers.” Well… really a stupid mistake. I called push_back several times, the vector size changed, reallocation occurs, and segmentation fault is my friend…

From this day onward, I’ll make a note to use [] whenever I need to change the size of a vector.