# ctype

ISO C++
ctype

## Implementation

### Specializations

For the required specialization `codecvt<wchar_t, char, mbstate_t>`, conversions are made between the internal character set (always UCS4 on GNU/Linux) and whatever the currently selected locale for the `LC_CTYPE` category implements.

The two required specializations are implemented as follows:

`ctype<char>`

This is simple specialization. Implementing this was a piece of cake.

`ctype<wchar_t>`

This specialization, by specifying all the template parameters, pretty much ties the hands of implementors. As such, the implementation is straightforward, involving `mcsrtombs` for the conversions between char to wchar_t and `wcsrtombs` for conversions between wchar_t and char.

Neither of these two required specializations deals with Unicode characters.

## Future

- How to deal with the global locale issue?

- How to deal with types other than char, wchar_t?

- Overlap between codecvt/ctype: narrow/widen

- mask typedef in `codecvt_base`, argument types in codecvt. what is know about this type?

- Why mask* argument in codecvt?

- Can this be made (more) generic? is there a simple way to straighten out the configure-time mess that is a by-product of this class?

- Get the ctype<wchar_t>::mask stuff under control. Need to make some kind of static table, and not do lookup every time somebody hits the `do_is...` functions. Too bad we can't just redefine mask for `ctype<wchar_t>`

- Rename abstract base class. See if just smash-overriding is a better approach. Clarify, add sanity to naming.

## Bibliography

The GNU C Library McGrath Roland Drepper Ulrich 2007 FSF Chapters 6 Character Set Handling and 7 Locales and Internationalization
Correspondence Drepper Ulrich 2002
ISO/IEC 14882:1998 Programming languages - C++ 1998 ISO
ISO/IEC 9899:1999 Programming languages - C 1999 ISO

### The Open Group Base Specifications, Issue 6 (IEEE Std. 1003.1-2004)

1999
The Open Group/The Institute of Electrical and Electronics Engineers, Inc.
The C++ Programming Language, Special Edition Stroustrup Bjarne 2000 Addison Wesley, Inc. Appendix D Addison Wesley
Standard C++ IOStreams and Locales Advanced Programmer's Guide and Reference Langer Angelika Kreft Klaus 2000 Addison Wesley Longman, Inc. Addison Wesley Longman