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typedef std::basic_ifstream<char> Stream;
Stream fileStream;
try {
fileStream.open(Name().c_str(), std::ios_base::binary);
if (fileStream.is_open()) {
typedef std::istream_iterator<ColourType, Stream::char_type> Iter;
bool const test2(Iter() == Iter(fileStream));

Why is test2 set to true? The file being read is ok. ColorType is a 32
bit integer.

Fraser.

Fraser Ross wrote:
> typedef std::basic_ifstream<char> Stream;
> Stream fileStream;
> try {
> fileStream.open(Name().c_str(), std::ios_base::binary);
> if (fileStream.is_open()) {
> typedef std::istream_iterator<ColourType, Stream::char_type> Iter;
> bool const test2(Iter() == Iter(fileStream));
>
> Why is test2 set to true? The file being read is ok. ColorType is
> a 32 bit integer.
>
> Fraser.

I believe the iterator constructor is allowed to read ahead one value
(and cache it). If that fails for some reason, the iterator will be
equal to the end-of-file iterator.


Bo Persson

"Bo Persson"
> I believe the iterator constructor is allowed to read ahead one value
> (and cache it). If that fails for some reason, the iterator will be
> equal to the end-of-file iterator.


I think I've made a basic mistake expecting to be able to read anything
other than characters from a stream opened in binary mode. It would be
useful if it was indicated somehow even at runtime after a debug build.

Fraser.

On Feb 19, 8:35 pm, "Fraser Ross" <z...@z.com> wrote:
> typedef std::basic_ifstream<char> Stream;
> Stream fileStream;
> try {
> fileStream.open(Name().c_str(), std::ios_base::binary);
> if (fileStream.is_open()) {
> typedef std::istream_iterator<ColourType, Stream::char_type> Iter;
> bool const test2(Iter() == Iter(fileStream));

> Why is test2 set to true? The file being read is ok. ColorType is a 32
> bit integer.

The istream_iterators read ahead. (They have to, in order to
know when end of file is reached *before* they are
dereferenced.) You haven't told us what the file contains, but
the istream_iterators use << to read: a formatted input
function. If the data in the input stream is not formatted
correctly---for an integer, this means that the next non white
space is a digit or a sign followed by a digit, the input fails,
which terminates the iteration.

After the end of the iteration, it might be useful to check why
the iteration terminated: if !fileStream.eof(), it was due to
a format error (or some hardware failure, if fileStream.bad()).

--
James Kanze

On Feb 20, 2:13 pm, "Fraser Ross" <z...@z.com> wrote:
> "Bo Persson"

> > I believe the iterator constructor is allowed to read ahead one value
> > (and cache it). If that fails for some reason, the iterator will be
> > equal to the end-of-file iterator.

> I think I've made a basic mistake expecting to be able to read anything
> other than characters from a stream opened in binary mode. It would be
> useful if it was indicated somehow even at runtime after a debug build.

If what was indicated? It's up to you to check the istream's
state, if it is relevant to your program. (It almost always is
when reading from a file. When reading from an istringstream
initialized from a text box in a window, or something like that,
it might not be.)

--
James Kanze