Re: [boost] [string_algo] ilexicographical_compare()/is_iless() bug?

Subject: Re: [boost] [string_algo] ilexicographical_compare()/is_iless() bug?
From: Olaf van der Spek (ml_at_[hidden])
Date: 2012-04-08 12:50:50

On Sun, Apr 8, 2012 at 3:46 PM, Dmitry Vinogradov <sraider_at_[hidden]> wrote:
> I want to share a problem using ilexicographical_compare().
>
> I think that ilexicographical_compare() must compare two strings in
> "alphabetical" order, the order letters appear in alphabet.
> But ilexicographical_compare() uses is_iless() to compare letters.
> And such comparison looks like:
> std::toupper<T1>(Arg1,m_Loc)<std::toupper<T2>(Arg2,m_Loc);

I think this isn't right either. If you've got both "A" and "a", the
order appears to be undefined.

> So, in fact, letters are compared depending on their position in a charset.
> It's not always match the alphabet order. Examples are Cyrillic letters "Io"
> and "i" (Unicode 0451 and 0456).
>
> I think the right solution is to compare like this:
> T1 Ch1 = std::toupper<T1>(Arg1,m_Loc);
> T2 Ch2 = std::toupper<T2>(Arg2,m_Loc);
> return std::use_facet< std::collate<typename CharType> >
> (m_Loc).compare(&Ch1, &Ch1 + 1, &Ch2, &Ch2 + 1);

The idea sounds reasonable.

Olaf