Hello, I'm trying to construct a string using an istream_iterator.
However, the resulting string is always empty. I was originally using
a file stream, but the same thing happens with a stringstream too.
Here's a simple example:

stringstream sstr("ABCD");
istream_iterator<char> it1(sstr);
istream_iterator<char> it2(sstr);

++it2;
++it2;

string str22(it1, it2);


Thanks.

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sharlene....@googlemail.com wrote:
> Hello, I'm trying to construct a string using an istream_iterator.
> However, the resulting string is always empty. I was originally using
> a file stream, but the same thing happens with a stringstream too.
> Here's a simple example:
>
> stringstream sstr("ABCD");
> istream_iterator<char> it1(sstr);
> istream_iterator<char> it2(sstr);
>
> ++it2;
> ++it2;
>
> string str22(it1, it2);

It is simply not how istream_iterator works. Two istream_iterators
that are not at the end of the stream are never equal to each other;
and conversely, the only case where i1==i2 is when both are end-of-
stream iterators. So, the only way to define a range using
istream_iterators is to specify the end-of-stream iterator as the end
of the range.

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On 16 août, 04:08, sharlene....@googlemail.com wrote:
> Hello, I'm trying to construct a string using an istream_iterator.
> However, the resulting string is always empty. I was originally using
> a file stream, but the same thing happens with a stringstream too.
> Here's a simple example:
>
> stringstream sstr("ABCD");
> istream_iterator<char> it1(sstr);
> istream_iterator<char> it2(sstr);
>
> ++it2;
> ++it2;
>
> string str22(it1, it2);

it1 and it2 are equal.
Therefore the range is empty.


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On Aug 16, 3:08 am, sharlene....@googlemail.com wrote:
> Hello, I'm trying to construct a string using an istream_iterator.
> However, the resulting string is always empty. I was originally using
> a file stream, but the same thing happens with a stringstream too.
> Here's a simple example:
> [snipped]

The istream_iterator class models the Input Iterator concept. Input
iterators are single pass and can not be used as "pointers" into a
container, as your example seem to expect. Input iterators have very
restricted requirements. See

http://oopweb.com/CPP/Documents/STL/Volume/prw421.htm

In particular, "for input iterators r and s, r==s does not imply ++r
== ++s."

For more information about iterator concepts, search the web.

Regards,
Vidar Hasfjord


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On 17 août, 05:27, Mathias Gaunard <loufo...@gmail.com> wrote:

> it1 and it2 are equal.
> Therefore the range is empty.

Oops, didn't read well.
I thought you incremented it1 and it2.


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