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From: Ray on 14 Nov 2009 13:56
Hello,

The intent of the following code is to read the first 2 characters from each
line until EOF is reached. It does this correctly on the first line but
stores an empty string for all subsequent lines. Of course I an accomplish
this task in other ways but I was wondering why this approach didn't work.

Thanks


char buf[512];

while (!cin.getline(buf, 3).eof())
{
cout << buf << '\n';
cin.ignore(100, '\n');
}

From: Scot Brennecke on 14 Nov 2009 16:11
Ray wrote:
> Hello,
>
> The intent of the following code is to read the first 2 characters from each
> line until EOF is reached. It does this correctly on the first line but
> stores an empty string for all subsequent lines. Of course I an accomplish
> this task in other ways but I was wondering why this approach didn't work.
>
> Thanks
>
>
> char buf[512];
>
> while (!cin.getline(buf, 3).eof())
> {
> cout<< buf<< '\n';
> cin.ignore(100, '\n');
> }
>

This is why I don't like the iostream classes. After the initial
getline, the state has been set with failbit. It must be reset or
something. I hate these classes and never use them. :)
From: David Wilkinson on 14 Nov 2009 16:21
Ray wrote:
> Hello,
>
> The intent of the following code is to read the first 2 characters from each
> line until EOF is reached. It does this correctly on the first line but
> stores an empty string for all subsequent lines. Of course I an accomplish
> this task in other ways but I was wondering why this approach didn't work.

Try like this

#include <iostream>
#include <string>
using namespace std;

int main()
{
string s;
while (getline(cin, s) && !s.empty())
{
cout.write(s.c_str(), 2) << "\n";
}
return 0;
}

--
David Wilkinson
Visual C++ MVP
From: Ray on 14 Nov 2009 17:54


"David Wilkinson" wrote:

> Ray wrote:
> > Hello,
> >
> > The intent of the following code is to read the first 2 characters from each
> > line until EOF is reached. It does this correctly on the first line but
> > stores an empty string for all subsequent lines. Of course I an accomplish
> > this task in other ways but I was wondering why this approach didn't work.
>
> Try like this
>
> #include <iostream>
> #include <string>
> using namespace std;
>
> int main()
> {
> string s;
> while (getline(cin, s) && !s.empty())
> {
> cout.write(s.c_str(), 2) << "\n";
> }
> return 0;
> }
>
> --
> David Wilkinson
> Visual C++ MVP
> .
>

David,

Thanks for your suggestion. However, my issue here is not how to accomplish
the task, which I can do, but rather, what precisely is wrong with the
approach I took in the code sample I provided.

Ray

From: Mateusz Loskot Mateusz on 15 Nov 2009 14:38
"Scot Brennecke" wrote:

> Ray wrote:
> > Hello,
> >
> > The intent of the following code is to read the first 2 characters from each
> > line until EOF is reached. It does this correctly on the first line but
> > stores an empty string for all subsequent lines. Of course I an accomplish
> > this task in other ways but I was wondering why this approach didn't work.
> >
> > Thanks
> >
> >
> > char buf[512];
> >
> > while (!cin.getline(buf, 3).eof())
> > {
> > cout<< buf<< '\n';
> > cin.ignore(100, '\n');
> > }
> >
>
> This is why I don't like the iostream classes. After the initial
> getline, the state has been set with failbit. It must be reset or
> something. I hate these classes and never use them. :)

This is a well-known and standard behaviour and
Stephan T. Lavavej explains it extensively here:

ID:351636 "STL: ifstream::getline() doesn't set eof flag"

https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=351636

Best regards,
--
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org
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