Re: G++ takes code, Comeau barfs with "error: qualified name is not allowed"

From:
red floyd <redfloyd@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Wed, 28 Jan 2009 08:46:30 -0800 (PST)
Message-ID:
<fc1a0ca8-ca17-44f2-aaf5-5d1e6e5b00df@p36g2000prp.googlegroups.com>
On Jan 28, 5:32 am, James Kanze <james.ka...@gmail.com> wrote:

On Jan 28, 1:02 am, Jeff Schwab <j...@schwabcenter.com> wrote:

red floyd wrote:

As far as I can tell, this code should be correct. G++ likes it, =

but

Comeau online hates it.
  std::vector<line_t> v(
    std::istream_iterator<line_t>(std::cin),
    std::istream_iterator<line_t>());

Comeau is mistaking this statement for a function declaration.
I believe Comeau is at fault, but I would love to be
corrected.


It's an interesting question. It looks like a function
declaration. But as Comeau says, the argument in a function
declaration cannot take a qualified name, so it can't be a
(legal) function declaration. Whether this is enough to
disqualify it as a function declaration or not, however, I don't
know. (If instead of std::cin, he had written just cin, or used
the name of a local variable, there would be no doubt that it
was a function declaration.)

You can
work around this issue with:

   std::istream_iterator<line_t> in(std::cin), end;
   std::vector<line_t> v(in, end);


The more or less standard solution is to put an extra pair of
parentheses around the arguments, e.g.:

  std::vector<line_t> v(
    (std::istream_iterator<line_t>(std::cin)),
    (std::istream_iterator<line_t>()));

(Putting them around either of the arguments is sufficient, but
there's no harm in being consistent.)


Thanks, guys. I didn't realize I'd hit the "most vexing parse". I'm
familiar with the issue,
but for some reason, it blew right by me. Go figure.

Thanks!

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