Re: Behaviour of istream_iterator on closed stream

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Wed, 29 Jul 2009 09:48:59 +0200

Message-ID:

<h4ovaq$4c7$1@news.eternal-september.org>

* Ian Collins:

Old Wolf wrote:

Code snippet:

std::ifstream file( "does_not_exist" );

You should have tested the state of file before going any further. It's
a pity this std::ifstream constructor doesn't throw an exception.

    std::vector<char> file_vec;
    std::copy( std::istream_iterator<char>(file),
std::istream_iterator<char>(), std::back_inserter(file_vec) );
    if ( file_vec.empty() )
            // file did not exist or had no contents..

I expected this to work, and have the istream_iterator for
closed file return a blank iterator, so the copy would not
copy anything. But it segfaults. Is the behaviour
undefined or is my compiler broken?

I think all bets are off, the std::ifstream object isn't fully initialised.

Hm. It is perhaps well known to you that I'm not very enthusiastic about
iostreams, but I find that hard to believe. Is it really true?

Yeah, I remember something about internal two-phase construction with an Init_
call or something, very bad.

But still -- how could one check for success if the object isn't fully
initialized?

Cheers,

- Alf