🚀 go-pugleaf

Hi,
Trying the new feature of throwing stream exceptions
i wrote the following program:

------------------------ snip ----------------------
#include <iostream>
#include <cstdlib>
using namespace std;


/* process and print sum of integer read from cin
 */
int main()
{
   
    cin.exceptions (ios::failbit | ios::badbit);

    try {
        int value, sum;

        /* while not EOF
         * read and add value
         */
        sum = 0;
#ifdef VERSION1
        while (cin >> ws) {
            cin >> value;
#else
        while (cin >> value) {
#endif
            sum += value;
        }

        cout << "sum: " << sum << endl;

    }
    catch (ios::failure error) {
        cerr << "Error: " << error.what() << endl;
        exit (EXIT_FAILURE);
    }
}
------------------------ snip ----------------------

But it didn't work as I expected, because also on EOF
I ALWAYS got the failbit exception!
And that happened in both versions.
After some investigation I found the problem and was surprised,
because the compiler and library I used had no bug.
Its a feature, which we should change IMHO.

The problem is, that istream::ipfx() always calls setstate(failbit),
if after any preparation good() is false.
So even if only the eofbit is set (due to the skip of whitespace),
the failbit is also set.
I think, therefore we must change the specification of ixpf()
to call setstate(eofbit) if eof() is true and setstate(failbit)
if any other problem occurs.

But even if that would be fixed, i would have problems implementing
a simple filter like:
    char c;
    while (cin.get(c)) {
	cout.put(c);
    }
With the actual specification i see no chance to get no exception on
EOF but an exception for any failure.
Therefore perhaps a deeper change in the specification would be
necessary, namely
 - either don't set failbit if eofbit is set
 - or set eofbit on eof and set the failbit with the NEXT try to read data
In general I need a chance to handle eof without getting
failbit exceptions.

ONE OTHER POINT I found:
You might say, that i could catch all exceptions and look at the
bits.
BUT i got no information about the reason for I/O exceptions.
I have only what() to get a
undefined message, but I think informations about the stream
or at least about the state of the stream would be senseful
to process exceptions on EOF different from other problems.
So for ios_base::failure an additional member like
state, which is rdstate() of the stream would be very senseful.

For example I'd like to open file and process its data until EOF
without any exception, but having exceptions for any error
and the information to handle it properly.
If for example i open 2 files i have no chance to check
which file got the problem.

Please correct me if I'am wrong or don't see any simple solution.
--------
Nico                             address: BREDEX GmbH
email:   nico@bredex.de                   Nicolai Josuttis
                                          Fallersleber-Tor-Wall 23
phone:   +49 531 24330-0                  D-38100 Braunschweig
fax:     +49 531 24330-99                 Germany
--------
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