CODEWITHSUNDEEP
c++
kasha
kasha

Reputation: 21

resetting a global iterator to a list 

#include<list>
#include<iostream>

using namespace std;

list<int> DL,TRS;
list<int>::iterator gitr;

void exchange();

int main() {
  DL.push_back(10);
  gitr=DL.begin();
  TRS.push_back(11);
  TRS.push_back(12);
  exchange();
  cout<<(*gitr)<<endl;
}

void exchange() {
  list<int> tdl;
  tdl=DL;
  DL.clear();
  DL=TRS;
  list<int>::iterator tmpitr=DL.begin();
  for(;tmpitr!=DL.end();++tmpitr)
     cout<<(*tmpitr)<<endl;
  DL.clear();
  DL=tdl;
}

This outputs 11 instead of 10. Why?

Upvotes: 1

Views: 669

Answers (1)

Bj&#246;rn Pollex
Bj&#246;rn Pollex

Reputation: 76848

This program invokes undefined behavior, and is therefore allowed to do anything it wants - even printing 11 instead of 10.

Why is it UB? Because gitr is assigned DL.begin(), and then (inside the function exchange) DL is cleared, making gitr an invalid iterator. Dereferencing that iterator is UB.

Upvotes: 2

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