Patch implementing n3654 (quoted strings)

[Howard Hinnant]

On Jul 9, 2013, at 10:10 AM, Marshall Clow <mclow.lists at gmail.com> wrote:

> A more substantial patch than the last two.
> Reference:
> 	http://wiki.edg.com/twiki/pub/Wg21bristol/FormalMotions/N3654.html
> 
> Needs more tests - and I'm working on those.

Thanks Marshall!

Comments:

*  Comments section in <iomanip> needs to be tagged with C++14.

*  The spec says to compare characters using operator== instead of _Traits::eq.  I have no idea why. I think what you did is what the spec should say.  But we need to follow the spec, or submit an issue, and implement the most likely outcome of that issue.

*  Everything starting with this line:

   template <class _CharT, class Iter, class _Traits=char_traits<_CharT>>

Needs to be macro-protected (e.g. Iter, quoted_output_proxy, first, etc.).

*  Not exception safe:

    ios_base::fmtflags saved_flags = __is.flags ();
    __is >> noskipws;

    ...

    __is.flags ( saved_flags );


Search for "__save_flags" in <random> for an example of how this should be handled.  We may want to move __save_flags to a common ancestor include so that both iomanip and random can use it.

*      __is >> noskipws;

This is the most expensive way to turn off skipws.  noskipws(__is) is faster.

*  Stylistic:  I prefer !__is.fail() to !__is.good().  The former says I failed to read in a character.  The latter says the stream is no longer in a state where it can read any more characters.  The difference can be eof().  In practice, the last character that gets read in does not set eof().  But the last int that gets read in does set eof() if there is no white space beyond it.  This is a very subtle distinction.  The upside is that you can get away with !is.good() only for characters, and not for any other type.  !is.fail() always works.

*  Tests: looking good.  Agree they need to be filled out a little more.  The missing quote cases should be tested for their correct result.  Test with skipws on and off and ensure it gets set back to the original.  Test output of non-const lvalue std::string.  Test std::wstring.  Test custom delimeter and escape.  Test unquote for zero-sized strings.

Thanks for working this!

Howard