Why do c++ programmers use != instead of <

Question

In c++ primer, pg 95 the author says that c++ programmers tend to use != in preference of < when writing loops.

for (vector<int>::size_type i = 0; i != 10; ++i) is preferred instead of  for (vector<int>::size_type i = 0; i < 10; ++i)  

I read the same thing in accelerated c++. Can someone explain the rationale behind this

Answer 1

When using some kinds of STL iterators (those that aren't random access), you must use !=:

for (map<int,int>::iterator i = a.begin(); i != a.end(); ++i) ... 

However, I don't see any reason to prefer != for well-ordered scalar types as in your example. I would usually prefer < for scalar types and != for all iterator types.

Answer 2

It's a habit for generic programming; for example, you can easiely use < with indices, but you cannot use that with all iterator types. A list iterator cannot efficiently implement < - however, != can be implemented for even the simplest of iterator types. Therefore, it is a good habit to always use the most generic comparison - it makes your code more resilient to change.