ifstream::get() surprise

From: Jacek Dziedzic (jacek__NOSPAM___at_janowo.net)
Date: 08/26/04 

Date: Thu, 26 Aug 2004 18:21:45 +0200

   Hi!

   Consider the following program

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

int main() {
   ifstream in("test.txt");
   char buf[40];
   in.get(buf,40);
   cerr << "Read: *" << buf << "*, trouble: " << !in << endl;
}

and a file, test.txt, starting with an empty line, ie. a lone EOL
character on the first line.

   I was quite surprised to find out, that under these circumstances
the aforementioned program produced
"Read **, trouble: 1".

   Why does 'in' go to a fail state? I thought 'get' reads up to
the terminator, stores all characters into 'buf' and leaves the
terminator inside the stream. That would mean 'buf' containing
just a \0 char (no chars read), the EOL still in the stream, but
why a failed state? There are more lines in the file, so we're
not eof(), and my understanding of this situation is a
"successful read of zero characters" rather than "read error".

   How then can I distinguish a successfull reading of an empty
line from an I/O error during reading a line? Of course I have
no a priori knowledge if these empty lines exist in my parsed
file or not.

TIA,
- J.

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