Re: Behaviour of istream_iterator on closed stream
On Jul 29, 9:18 am, Ian Collins <ian-n...@hotmail.com> wrote:
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.
That's very discutable. You have to check the status anyway,
after every read, so there's no invariant that you haven't been
able to establish.
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?
Either your compiler is broken, or (more likely) you have
undefined behavior elsewhere which has corrupted memory, and
caused it to fail here.
Try creating a minimum sized program which displays the error.
(If you do nothing but the above in main, and it crashes, you
do have a compiler problem. It works with g++, Sun CC and VC++,
however.)
I think all bets are off, the std::ifstream object isn't fully
initialised.
If you return from the constructor, the object is fully
initialized. By definition, for starters:-)---what doesn't take
place in the constructor isn't considered initialization. But
in the case of std::ifstream (and all of the object types
defined in the standard), the constructor is required to ensure
that the object is usable as usual. (I'd still check for an
error after construction, but before the copy, since the type of
error you want to report will be different if the file doesn't
exist.)
--
James Kanze (GABI Software) email:james.kanze@gmail.com
Conseils en informatique orient=E9e objet/
Beratung in objektorientierter Datenverarbeitung
9 place S=E9mard, 78210 St.-Cyr-l'=C9cole, France, +33 (0)1 30 23 00 34