Author: bkoz@redhat.com (Benjamin Kosnik)
Keywords: HOWTO, libstdc++, locale name LC_ALL

# Notes on the locale implementation.

prepared by Benjamin Kosnik (bkoz@redhat.com) on October 14, 2002

## 1. Abstract

Describes the basic locale object, including nested classes id, facet, and the reference-counted implementation object, class _Impl.

## 2. What the standard says

Class locale is non-templatized and has two distinct types nested inside of it:

> class facet 22.1.1.1.2 Class locale::facet

Facets actually implement locale functionality. For instance, a facet called numpunct is the data objects that can be used to query for the thousands separator is in the German locale.

Literally, a facet is strictly defined:

- containing the following public data member:

  `static locale::id id;`

- derived from another facet:

  `class gnu_codecvt: public std::ctype<user-defined-type>`

Of interest in this class are the memory management options explicitly specified as an argument to facet's constructor. Each constructor of a facet class takes a std::size_t __refs argument: if __refs == 0, the facet is deleted when the locale containing it is destroyed. If __refs == 1, the facet is not destroyed, even when it is no longer referenced.

> class id 22.1.1.1.3 - Class locale::id

Provides an index for looking up specific facets.

## 3. Interacting with "C" locales.

Some help on determining the underlying support for locales on a system. Note, this is specific to linux (and glibc-2.3.x)

- ``locale -a`` displays available locales.

  >     af_ZA
  >     ar_AE
  >     ar_AE.utf8
  >     ar_BH
  >     ar_BH.utf8
  >     ar_DZ
  >     ar_DZ.utf8
  >     ar_EG
  >     ar_EG.utf8
  >     ar_IN
  >     ar_IQ
  >     ar_IQ.utf8
  >     ar_JO
  >     ar_JO.utf8
  >     ar_KW
  >     ar_KW.utf8
  >     ar_LB
  >     ar_LB.utf8
  >     ar_LY
  >     ar_LY.utf8
  >     ar_MA
  >     ar_MA.utf8
  >     ar_OM
  >     ar_OM.utf8
  >     ar_QA
  >     ar_QA.utf8
  >     ar_SA
  >     ar_SA.utf8
  >     ar_SD
  >     ar_SD.utf8
  >     ar_SY
  >     ar_SY.utf8
  >     ar_TN
  >     ar_TN.utf8
  >     ar_YE
  >     ar_YE.utf8
  >     be_BY
  >     be_BY.utf8
  >     bg_BG
  >     bg_BG.utf8
  >     br_FR
  >     bs_BA
  >     C
  >     ca_ES
  >     ca_ES@euro
  >     ca_ES.utf8
  >     ca_ES.utf8@euro
  >     cs_CZ
  >     cs_CZ.utf8
  >     cy_GB
  >     da_DK
  >     da_DK.iso885915
  >     da_DK.utf8
  >     de_AT
  >     de_AT@euro
  >     de_AT.utf8
  >     de_AT.utf8@euro
  >     de_BE
  >     de_BE@euro
  >     de_BE.utf8
  >     de_BE.utf8@euro
  >     de_CH
  >     de_CH.utf8
  >     de_DE
  >     de_DE@euro
  >     de_DE.utf8
  >     de_DE.utf8@euro
  >     de_LU
  >     de_LU@euro
  >     de_LU.utf8
  >     de_LU.utf8@euro
  >     el_GR
  >     el_GR.utf8
  >     en_AU
  >     en_AU.utf8
  >     en_BW
  >     en_BW.utf8
  >     en_CA
  >     en_CA.utf8
  >     en_DK
  >     en_DK.utf8
  >     en_GB
  >     en_GB.iso885915
  >     en_GB.utf8
  >     en_HK
  >     en_HK.utf8
  >     en_IE
  >     en_IE@euro
  >     en_IE.utf8
  >     en_IE.utf8@euro
  >     en_IN
  >     en_NZ
  >     en_NZ.utf8
  >     en_PH
  >     en_PH.utf8
  >     en_SG
  >     en_SG.utf8
  >     en_US
  >     en_US.iso885915
  >     en_US.utf8
  >     en_ZA
  >     en_ZA.utf8
  >     en_ZW
  >     en_ZW.utf8
  >     es_AR
  >     es_AR.utf8
  >     es_BO
  >     es_BO.utf8
  >     es_CL
  >     es_CL.utf8
  >     es_CO
  >     es_CO.utf8
  >     es_CR
  >     es_CR.utf8
  >     es_DO
  >     es_DO.utf8
  >     es_EC
  >     es_EC.utf8
  >     es_ES
  >     es_ES@euro
  >     es_ES.utf8
  >     es_ES.utf8@euro
  >     es_GT
  >     es_GT.utf8
  >     es_HN
  >     es_HN.utf8
  >     es_MX
  >     es_MX.utf8
  >     es_NI
  >     es_NI.utf8
  >     es_PA
  >     es_PA.utf8
  >     es_PE
  >     es_PE.utf8
  >     es_PR
  >     es_PR.utf8
  >     es_PY
  >     es_PY.utf8
  >     es_SV
  >     es_SV.utf8
  >     es_US
  >     es_US.utf8
  >     es_UY
  >     es_UY.utf8
  >     es_VE
  >     es_VE.utf8
  >     et_EE
  >     et_EE.utf8
  >     eu_ES
  >     eu_ES@euro
  >     eu_ES.utf8
  >     eu_ES.utf8@euro
  >     fa_IR
  >     fi_FI
  >     fi_FI@euro
  >     fi_FI.utf8
  >     fi_FI.utf8@euro
  >     fo_FO
  >     fo_FO.utf8
  >     fr_BE
  >     fr_BE@euro
  >     fr_BE.utf8
  >     fr_BE.utf8@euro
  >     fr_CA
  >     fr_CA.utf8
  >     fr_CH
  >     fr_CH.utf8
  >     fr_FR
  >     fr_FR@euro
  >     fr_FR.utf8
  >     fr_FR.utf8@euro
  >     fr_LU
  >     fr_LU@euro
  >     fr_LU.utf8
  >     fr_LU.utf8@euro
  >     ga_IE
  >     ga_IE@euro
  >     ga_IE.utf8
  >     ga_IE.utf8@euro
  >     gl_ES
  >     gl_ES@euro
  >     gl_ES.utf8
  >     gl_ES.utf8@euro
  >     gv_GB
  >     gv_GB.utf8
  >     he_IL
  >     he_IL.utf8
  >     hi_IN
  >     hr_HR
  >     hr_HR.utf8
  >     hu_HU
  >     hu_HU.utf8
  >     id_ID
  >     id_ID.utf8
  >     is_IS
  >     is_IS.utf8
  >     it_CH
  >     it_CH.utf8
  >     it_IT
  >     it_IT@euro
  >     it_IT.utf8
  >     it_IT.utf8@euro
  >     iw_IL
  >     iw_IL.utf8
  >     ja_JP.eucjp
  >     ja_JP.utf8
  >     ka_GE
  >     kl_GL
  >     kl_GL.utf8
  >     ko_KR.euckr
  >     ko_KR.utf8
  >     kw_GB
  >     kw_GB.utf8
  >     lt_LT
  >     lt_LT.utf8
  >     lv_LV
  >     lv_LV.utf8
  >     mi_NZ
  >     mk_MK
  >     mk_MK.utf8
  >     mr_IN
  >     ms_MY
  >     ms_MY.utf8
  >     mt_MT
  >     mt_MT.utf8
  >     nl_BE
  >     nl_BE@euro
  >     nl_BE.utf8
  >     nl_BE.utf8@euro
  >     nl_NL
  >     nl_NL@euro
  >     nl_NL.utf8
  >     nl_NL.utf8@euro
  >     nn_NO
  >     nn_NO.utf8
  >     no_NO
  >     no_NO.utf8
  >     oc_FR
  >     pl_PL
  >     pl_PL.utf8
  >     POSIX
  >     pt_BR
  >     pt_BR.utf8
  >     pt_PT
  >     pt_PT@euro
  >     pt_PT.utf8
  >     pt_PT.utf8@euro
  >     ro_RO
  >     ro_RO.utf8
  >     ru_RU
  >     ru_RU.koi8r
  >     ru_RU.utf8
  >     ru_UA
  >     ru_UA.utf8
  >     se_NO
  >     sk_SK
  >     sk_SK.utf8
  >     sl_SI
  >     sl_SI.utf8
  >     sq_AL
  >     sq_AL.utf8
  >     sr_YU
  >     sr_YU@cyrillic
  >     sr_YU.utf8
  >     sr_YU.utf8@cyrillic
  >     sv_FI
  >     sv_FI@euro
  >     sv_FI.utf8
  >     sv_FI.utf8@euro
  >     sv_SE
  >     sv_SE.iso885915
  >     sv_SE.utf8
  >     ta_IN
  >     te_IN
  >     tg_TJ
  >     th_TH
  >     th_TH.utf8
  >     tl_PH
  >     tr_TR
  >     tr_TR.utf8
  >     uk_UA
  >     uk_UA.utf8
  >     ur_PK
  >     uz_UZ
  >     vi_VN
  >     vi_VN.tcvn
  >     wa_BE
  >     wa_BE@euro
  >     yi_US
  >     zh_CN
  >     zh_CN.gb18030
  >     zh_CN.gbk
  >     zh_CN.utf8
  >     zh_HK
  >     zh_HK.utf8
  >     zh_TW
  >     zh_TW.euctw
  >     zh_TW.utf8

- ``locale`` displays environmental variables that impact how locale("") will be deduced.

  >     LANG=en_US
  >     LC_CTYPE="en_US"
  >     LC_NUMERIC="en_US"
  >     LC_TIME="en_US"
  >     LC_COLLATE="en_US"
  >     LC_MONETARY="en_US"
  >     LC_MESSAGES="en_US"
  >     LC_PAPER="en_US"
  >     LC_NAME="en_US"
  >     LC_ADDRESS="en_US"
  >     LC_TELEPHONE="en_US"
  >     LC_MEASUREMENT="en_US"
  >     LC_IDENTIFICATION="en_US"
  >     LC_ALL=

From Josuttis, p. 697-698, which says, that "there is only *one* relation (of the C++ locale mechanism) to the C locale mechanism: the global C locale is modified if a named C++ locale object is set as the global locale" (emphasis Paolo), that is:

`std::locale::global(std::locale(""));`

affects the C functions as if the following call was made:

`std::setlocale(LC_ALL, "");`

On the other hand, there is *no* viceversa, that is, calling setlocale has *no* whatsoever on the C++ locale mechanism, in particular on the working of locale(""), which constructs the locale object from the environment of the running program, that is, in practice, the set of LC_ALL, LANG, etc. variable of the shell.

## 4. Design

The major design challenge is fitting an object-orientated and non-global locale design ontop of POSIX and other relevant stanards, which include the Single Unix (nee X/Open.)

Because POSIX falls down so completely, portibility is an issue.

class _Impl The internal representation of the std::locale object.

## 5. Examples

More information can be found in the following testcases:

- testsuite/22_locale/all

## 6. Unresolved Issues

- locale initialization: at what point does _S_classic, _S_global get initialized? Can named locales assume this initialization has already taken place?
- document how named locales error check when filling data members. Ie, a fr_FR locale that doesn't have numpunct::truename(): does it use "true"? Or is it a blank string? What's the convention?
- explain how locale aliasing happens. When does "de_DE" use "de" information? What is the rule for locales composed of just an ISO language code (say, "de") and locales with both an ISO language code and ISO country code (say, "de_DE").
- what should non-required facet instantiations do? If the generic implemenation is provided, then how to end-users provide specializations?

## 7. Acknowledgments

## 8. Bibliography / Referenced Documents

Drepper, Ulrich, GNU libc (glibc) 2.2 manual. In particular, Chapters "6. Character Set Handling" and "7 Locales and Internationalization"

Drepper, Ulrich, Numerous, late-night email correspondence

ISO/IEC 14882:1998 Programming languages - C++

ISO/IEC 9899:1999 Programming languages - C

Langer, Angelika and Klaus Kreft, Standard C++ IOStreams and Locales, Advanced Programmer's Guide and Reference, Addison Wesley Longman, Inc. 2000

Stroustrup, Bjarne, Appendix D, The C++ Programming Language, Special Edition, Addison Wesley, Inc. 2000

System Interface Definitions, Issue 6 (IEEE Std. 1003.1-200x) The Open Group/The Institute of Electrical and Electronics Engineers, Inc. http://www.opennc.org/austin/docreg.html