Re: changing istream default delimiter

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Tue, 31 Mar 2009 03:29:01 -0700 (PDT)
Message-ID:
<4d1cdb1b-6be2-4be4-b0ad-44f20ab8359f@k2g2000yql.googlegroups.com>
On Mar 31, 5:56 am, "Amadeus W.M." <amadeu...@verizon.net> wrote:

On Mon, 30 Mar 2009 02:39:21 -0700, James Kanze wrote:

It's also a hack, and abuse of the locale. As such, it can
only server to confuse the reader.


Meanwhile I've turned to boost tokenizer to parse a line,
which can handle commas within quotes too, so doing it using
facets is only a matter of curiosity now.


In other words, you're using a tool designed for the job, rather
than a tool designed for a different job.

FWIW, if you do want to change the definition of what istream
thinks is white space, you have to:

 1. Create an instance of a ctype<char> facet which defines
    white space as you want. Exceptionally (because creating
    new facets is normally anything but trivial), this is
    simple; the standard provides a specialization of ctype for
    char, which has a constructor which takes a table specifying
    the types of each char, so all you have to do is write the
    table and create an instance of this specialization.

    Note that locale reference counts facets, so you should use
    new to create the instance, and let locale itself take care
    of the delete.

 2. Create a locale using this facet. For this, you'd probably
    use the templated constructor template< typename Facet >
    std::locale::locale( std::locale const& other, Facet* ),
    which creates a copy of other, with the given facet
    replacing the one in the original locale.

 3. Imbue your stream with this locale.

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