Re: Query regarding iterators and vector

From:

prasadmpatil@gmail.com

Newsgroups:

comp.lang.c++

Date:

Fri, 4 Jul 2008 19:51:50 -0700 (PDT)

Message-ID:

<3f3e2d90-9c20-4482-804f-979c30669e01@m44g2000hsc.googlegroups.com>

Thank you all for the replies. I used a loop variable and
vector.size() instead of the iterator to solve my problem.

On Jul 4, 6:31 pm, "Daniel T." <danie...@earthlink.net> wrote:

prasadmpa...@gmail.com wrote:

I am new STL programming.
I have a query regarding vectors. If I am iterating over a vector
using a iterator, but do some operations that modify the size of the
vector. Will the iterator recognize this?

No.

A vector's iterators are invalidated when its memory is reallocate=

Additionally, inserting or deleting an element in the middle of a
vector invalidates all iterators that point to elements following =

the

   insertion or deletion point. It follows that you can prevent a
   vector's iterators from being invalidated if you use reserve() to
   preallocate as much memory as the vector will ever use, and if all
   insertions and deletions are at the vector's end.
   <http://www.sgi.com/tech/stl/Vector.html>

I wrote the following program to test this out.

Try adding "a.reserve(5);" at any point after 'a' is defined, and before
the loop.

#include <fstream>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main()
{
   vector<int> a;

   a.push_back(1);
   a.push_back(2);
   a.push_back(3);
   cout<<"Vector test begin"<<endl;
   vector<int>::iterator iter0;
   for(iter0=a.begin(); iter0!=a.end(); iter0++)
   {
           cout << "\n value: " << (*iter0)<<endl;
           if(*iter0 == 2)
           {
                   a.push_back(4);
                   a.push_back(5);
           }
   }
   cout<<"Vector test end";
}