Vector Insert Program

[DoABarrelRoll94]

Why is the "it" iterator no longer valid after line 13?

// inserting into a vector
#include <iostream>
#include <vector>

int main ()
{
  std::vector<int> myvector (3,100);
  std::vector<int>::iterator it;

  it = myvector.begin();
  it = myvector.insert ( it , 200 );

  myvector.insert (it,2,300);

  // "it" no longer valid, get a new one:
  it = myvector.begin();

  std::vector<int> anothervector (2,400);
  myvector.insert (it+2,anothervector.begin(),anothervector.end());

  int myarray [] = { 501,502,503 };
  myvector.insert (myvector.begin(), myarray, myarray+3);

  std::cout << "myvector contains:";
  for (it=myvector.begin(); it<myvector.end(); it++)
    std::cout << ' ' << *it;
  std::cout << '\n';

  return 0;
}

[jlb]

Because you inserted an element that possibly required the vector to be resized, invalidating the iterators.

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

Iterator validity
If a reallocation happens, all iterators, pointers and references related to the container are invalidated.
Otherwise, only those pointing to position and beyond are invalidated, with all iterators, pointers and references to elements before position guaranteed to keep referring to the same elements they were referring to before the call.

[AbstractionAnon]

Because the insert may have reallocated the vector.

http://www.cplusplus.com/reference/vector/vector/insert/?kw=vector%3A%3Ainsert
See the second sentence.

[DoABarrelRoll94]

Ok thank you guys for clearing that up.