What does "linguistic casing" mean?

by Michael S. Kaplan, published on 2004/12/11 09:51 -05:00, original URI: http://blogs.msdn.com/b/michkap/archive/2004/12/11/279942.aspx

The LCMapString API is the ultimate Win32 API that does casing. All of those functions in USER32 (CharUpper, CharLower, CharUpperBuff, and CharLowerBuff) are wrappers around calls to LCMapString with the LCMAP_UPPERCASE and LCMAP_LOWERCASE flags. All of these functions do the simple mappings like a --> A --> a, å --> Å --> å, etc.

For the most part, these mappings will properly roundtrip, which is a good thing since the mapping from lowercase to uppercase is used by the file system for its case insensitivity. All of these operations are linguistically sensible.

So what does LCMAP_LINGUISTIC_CASING mean? What happens when you pass that flag?

Well, two things:

1. You get the right behavior for Turkic locales like Turkish and Azeri;
2. You get a bunch of one-way mappings on all locales, e.g. U+03f1 (Greek Rho Symbol) will uppercase to U+03a1 (Capital Greek Rho), which will lowercase to U+03c1 (Small Greek Rho).

Now neither of these seems very "linguistic" to me. But they do fit into the Unicode Standard definitions of simple case mapping. Since both are described in Unicode, we should maybe have called it LCMAP_UNICODE_SIMPLE_CASING instead?

It is only the simple Unicode casing that is covered. No Microsoft products currently handle full Unicode casing, which can actually change the size of the target string.

Though we have our eye on this feature since it has been requested from time to time. Perhaps it would be higher on our list of things to do if more people were asking....

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