locale

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

Requirements 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 object that can be used to query for the thousands separator in the 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.

Design The major design challenge is fitting an object-orientated and non-global locale design on top of POSIX and other relevant standards, which include the Single Unix (nee X/Open.) Because C and earlier versions of POSIX fall down so completely, portability is an issue.

Implementation

Interacting with "C" locales 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* vice versa, 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.

Future 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. I.e., 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 implementation is provided, then how to end-users provide specializations?

Bibliography The GNU C Library McGrathRoland DrepperUlrich 2007 FSF Chapters 6 Character Set Handling and 7 Locales and Internationalization Correspondence DrepperUlrich 2002 ISO/IEC 14882:1998 Programming languages - C++ 1998 ISO ISO/IEC 9899:1999 Programming languages - C 1999 ISO <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://pubs.opengroup.org/onlinepubs/9699919799/"> System Interface Definitions, Issue 7 (IEEE Std. 1003.1-2008) </link> 2008 The Open Group/The Institute of Electrical and Electronics Engineers, Inc. The C++ Programming Language, Special Edition StroustrupBjarne 2000 Addison Wesley, Inc. Appendix D Addison Wesley Standard C++ IOStreams and Locales Advanced Programmer's Guide and Reference LangerAngelika KreftKlaus 2000 Addison Wesley Longman, Inc. Addison Wesley Longman