Re: Iterator questions...

From:

"Jim Langston" <tazmaster@rocketmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 15 May 2008 20:54:22 -0700

Message-ID:

<NA7Xj.172$J43.23@newsfe05.lga>

barcaroller wrote:

I've noticed that neither container.begin() nor container.end() return
an error when the container is empty, so I get a nasty segfault when I
dereference the iterator. Do I have to check if the container is
empty every time I use an iterator, or am I missing something?

You are missing something. For an empty containter .begin() == .end()

Aren't you checking to make sure your iteratores aren't equal to .end()?

One of the most common uses of .begin() and .end() is in a for loop, such
as:

std::list<int> Data;
for ( std::list<int>::iterator it = Data.begin(); it != Data.end(); ++it )
{
// it is guaranteed to be pointing to an item in the list
}

Other uses include passing them to algorithms, also as result of .find()
etc..

But in all cases you must ensure that your iterator != .end()

Speaking of iterators: if I initialize 'iter = container.end()', can I
count on iter to stay equal to container.end() even if elements are
deleted and added to the container?

Hmm.. I'm not sure. I do know that some operations on containers can
invalidate iterators. I'm fairly sure that this includes .end() which
points one past the last item in the container.

--
Jim Langston
tazmaster@rocketmail.com