How to get a reverse_iterator

[* Tong *]

Hi,

Simple question, how to get a reverse_iterator?

As you can see from the following code, I managed to answer the first half
of the question myself, but can't figure out the second half:

string line("FIRST,MIDDLE,LAST");

// find first element in a comma-separated list
string::iterator comma = find(line.begin(), line.end(), ',');
cout << string(line.begin(), comma) << endl;

cout << string(++comma, line.end()) << endl;

// get reverse_iterator from iterator
string::reverse_iterator commar = string::reverse_iterator(comma);
cout << string(line.rbegin(), commar) << endl;

// get reverse_iterator from reverse_iterator. wrong. how to fix?
cout << string(++comma, string::reverse_iterator(line.rbegin())) << endl;
Please help.

Thanks

tong

[Ian Collins]

* Tong * wrote:

Hi,

Simple question, how to get a reverse_iterator?

As you can see from the following code, I managed to answer the first half
of the question myself, but can't figure out the second half:

string line("FIRST,MIDDLE,LAST");

// find first element in a comma-separated list
string::iterator comma = find(line.begin(), line.end(), ',');
cout << string(line.begin(), comma) << endl;

cout << string(++comma, line.end()) << endl;

// get reverse_iterator from iterator
string::reverse_iterator commar = string::reverse_iterator(comma);
cout << string(line.rbegin(), commar) << endl;

// get reverse_iterator from reverse_iterator. wrong. how to fix?
cout << string(++comma, string::reverse_iterator(line.rbegin())) << endl;

It's not the initialising of the iterator that's the problem, it's the
attempt to construct a string from an iterator and a reverse_iterator.

--
Ian Collins.

[mastier_na_vsje_ruki]

* * // get reverse_iterator from reverse_iterator. wrong. how to fix?

* * cout << string(++comma, string::reverse_iterator(line.rbegin())) << endl;

Both arguments for string constructor should be either iterators or
reverse_iterators.
Besides I don't see the point of calling string::reverse_iterator copy
constructor with line.rbegin(). It won't convert the reverse_iterator
-- if that's what you've expected -- it'll just create another
reverse_iterator (only silently casting from const_reverse_iterator).
What's more - even if you changed ++comma to ++commar in the last
line, the string's ctor would fail because of invalid iterator range.

regards,
slaimi.

[Ensemble]

On Sat, 09 Aug 2008 20:21:10 -0700, mastier_na_vsje_ruki wrote:

>Â* Â* // get reverse_iterator from reverse_iterator. wrong. how to fix?
Â* Â* cout << string(++comma, string::reverse_iterator(line.rbegin())) << endl;

Both arguments for string constructor should be either iterators or
reverse_iterators.
Besides I don't see the point of calling string::reverse_iterator copy
constructor with line.rbegin(). It won't convert the reverse_iterator
-- if that's what you've expected -- it'll just create another
reverse_iterator (only silently casting from const_reverse_iterator).

So, as oppose to double-negative gives you positive, double reverse
iterator doesn't give you a normal iterator, correct?

thx

[Ian Collins]

Ensemble wrote:

On Sat, 09 Aug 2008 20:21:10 -0700, mastier_na_vsje_ruki wrote:

>> // get reverse_iterator from reverse_iterator. wrong. how to fix?
cout << string(++comma, string::reverse_iterator(line.rbegin())) << endl;

Both arguments for string constructor should be either iterators or
reverse_iterators.
Besides I don't see the point of calling string::reverse_iterator copy
constructor with line.rbegin(). It won't convert the reverse_iterator
-- if that's what you've expected -- it'll just create another
reverse_iterator (only silently casting from const_reverse_iterator).

So, as oppose to double-negative gives you positive, double reverse
iterator doesn't give you a normal iterator, correct?

Correct.

--
Ian Collins.