CODEWITHSUNDEEP
c++iterator
user3663882
user3663882

Reputation: 7357

Operator != for iterators in stdlibrary

It's clear why we cannot assign const_iterator to just iterator.

std::vector<int> v;
std::vector<int>::iterator i = v.cbegin(); //no viable convertion

But the fact that they'are compare equal in the != operator standpoint seems very confusing.

std::vector<int> v;
for(int i = 0; i < 10; i++)
    v.push_back(i);
for(std::vector<int>::const_iterator i = v.cbegin(); i!= v.end(); i++)
    std::cout << *i << std::endl; //prints 0-9

what's the reason for such behavior of != operator?

Upvotes: 0

Views: 31

Answers (1)

WorldSEnder
WorldSEnder

Reputation: 5044

Assigning a const iterator to an iterator would break const-correctness of the iterator. Consider:

 typedef std::vector<int> seq;
 const seq v;
 seq::const_iterator = v.cbegin(); // Okay
 // seq::iterator = v.begin(); // Not okay, sequence is const

If you could assign a const iterator to a simple iterator the above example would be able to manipulate the content of a const sequence.

Comparing two iterators just tells you if they point to the same data (or the end/begin) of some sequence.

 typedef std::vector<int> seq;
 seq v;
 const seq& cv = v;
 cv.cbegin() == v.begin(); // Okay
 cv.cbegin() != v.begin(); // Also okay

Here you have a sequence and a const view of the same sequence. When comparing iterators of the two, two iterators pointing to the same data should compare equals.

Upvotes: 2

Related Questions