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From: "Carey Evans" <carey DOT evans AT gmail DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: ctype<char> custom table lookup in C++
Date: 19 May 2005 16:41:32 -0700
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

I've been trying to write a custom C++ ctype<char> facet to support the
full range of characters in codepage 850, not just ASCII.  However,
I've run across a problem with the ctype<char>::is(mask,char) lookup on
the custom table I pass to the ctype<char> constructor.

The ISO C++ standard says of is(mask m, char c) that:

> The first form returns table()[(unsigned char)c] & m; ...

but with GCC 3.4.3 in DJGPP, it returns (from ctype_inline.h):

> _M_table[static_cast<unsigned char>(__c + 1)] & __m;

which means that all the character classifications in my custom class
are off by one.

On the other hand, the second form of is(const char*,const char*,mask*)
works with my custom table, but not with the ctype<char> from the
standard locale.

The correct solution appears to me to be to remove the "+ 1" from the
is() function, and add it to the ctype<char> constructors in
ctype_noninline.h to do something like:

> _M_table(__table ? __table : __dj_ctype_flags + 1)

-- 
Carey Evans