istream bug

istream bug

[Robert Schweikert]

When using the "ios::nocreate" opening mode on an istream the file
pointer moves to the end of the file which causes the read with the
stream operator ">>" to fail. I realize that using "ios::nocreate" on an
istream doesn't make a whole lot of sense, however, I think the compiler
should either ignore this opening mode on the istream or issue a warning
or error message. Putting the file pointer to the end of the file
produces behavior that is hard to track down.

The attached file illustrates the problem.

-> g++ -o strTestNb  strTest.C
-> ./strTestNb
First Flag: 0
Second Flag: 1
Third Flag: 0
This is buffer: Assembly-1
This is n: 1
This is i: 0
->

-> g++ -o strTest -DDEMOBUG strTest.C
-> ./strTest
This is i: 66267
This is i: 66268
This is i: 66269
This is i: 66270
This is i: 66271
This is i: 66272
This is i: 66273

This is an endless loop.

A fix is appreciated.

Thanks,
Robert


--
Robert Schweikert                      MAY THE SOURCE BE WITH YOU
rjschwei@mindspring.com                         LINUX

Re: istream bug

[Alexandre Oliva]

On Jan  4, 2001, Robert Schweikert <rjschwei@mindspring.com> wrote:

> When using the "ios::nocreate" opening mode on an istream the file
> pointer moves to the end of the file which causes the read with the
> stream operator ">>" to fail.

Wouldn't it be the case that you failed to specify that the stream is
for input?  By passing ios::nocreate, you overrode the default
argument that is ios::input (sp?), so you should have ORed
ios::nocreate to ios::input to get an input stream.  Yes, it's
counter-intuitive, but that's the way it is implemented.

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                  aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist    *Please* write to mailing lists, not to me

Re: Istream bug

[Benjamin Kosnik]

Please note that nocreate is not in iso 14882. As such it is no longer
supported.

-benjamin