bc225f98dd
2003-11-18 Jonathan Wakely <redi@gcc.gnu.org> * docs/html/configopts.html, docs/html/debug.html, docs/html/documentation.html, docs/html/explanations.html, docs/html/install.html, docs/html/17_intro/contribute.html, docs/html/17_intro/howto.html, docs/html/17_intro/license.html, docs/html/18_support/howto.html, docs/html/19_diagnostics/howto.html, docs/html/20_util/howto.html, docs/html/21_strings/howto.html, docs/html/22_locale/codecvt.html, docs/html/22_locale/ctype.html, docs/html/22_locale/howto.html, docs/html/22_locale/locale.html, docs/html/22_locale/messages.html, docs/html/23_containers/howto.html, docs/html/24_iterators/howto.html, docs/html/25_algorithms/howto.html, docs/html/26_numerics/howto.html, docs/html/27_io/howto.html, docs/html/ext/howto.html, docs/html/ext/sgiexts.html: Add <link> tags. From-SVN: r73712
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544 lines
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
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<meta name="AUTHOR" content="bkoz@redhat.com (Benjamin Kosnik)" />
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<meta name="KEYWORDS" content="HOWTO, libstdc++, locale name LC_ALL" />
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<meta name="DESCRIPTION" content="Notes on the locale implementation." />
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<title>Notes on the locale implementation.</title>
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<link rel="Help" href="../faq/index.html" type="text/html" title="F.A.Q." />
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</head>
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<body>
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<h1>
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Notes on the locale implementation.
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</h1>
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<em>
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prepared by Benjamin Kosnik (bkoz@redhat.com) on October 14, 2002
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</em>
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<h2>
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1. Abstract
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</h2>
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<p>
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Describes the basic locale object, including nested
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classes id, facet, and the reference-counted implementation object,
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class _Impl.
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</p>
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<h2>
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2. What the standard says
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</h2>
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Class locale is non-templatized and has two distinct types nested
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inside of it:
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<blockquote>
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<em>
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class facet
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22.1.1.1.2 Class locale::facet
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</em>
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</blockquote>
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<p>
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Facets actually implement locale functionality. For instance, a facet
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called numpunct is the data objects that can be used to query for the
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thousands separator is in the German locale.
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</p>
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Literally, a facet is strictly defined:
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<ul>
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<li>containing the following public data member:
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<p>
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<code>static locale::id id;</code>
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</p>
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</li>
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<li>derived from another facet:
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<p>
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<code> class gnu_codecvt: public std::ctype<user-defined-type></code>
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</p>
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</li>
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</ul>
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<p>
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Of interest in this class are the memory management options explicitly
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specified as an argument to facet's constructor. Each constructor of a
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facet class takes a std::size_t __refs argument: if __refs == 0, the
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facet is deleted when the locale containing it is destroyed. If __refs
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== 1, the facet is not destroyed, even when it is no longer
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referenced.
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</p>
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<blockquote>
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<em>
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class id
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22.1.1.1.3 - Class locale::id
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</em>
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</blockquote>
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<p>
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Provides an index for looking up specific facets.
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</p>
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<h2>
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3. Interacting with "C" locales.
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</h2>
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<p>
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Some help on determining the underlying support for locales on a system.
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Note, this is specific to linux (and glibc-2.3.x)
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</p>
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<ul>
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<li> <code>`locale -a`</code> displays available locales.
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<blockquote>
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<pre>
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af_ZA
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ar_AE
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ar_AE.utf8
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ar_BH
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ar_BH.utf8
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ar_DZ
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ar_DZ.utf8
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ar_EG
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ar_EG.utf8
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ar_IN
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ar_IQ
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ar_IQ.utf8
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ar_JO
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ar_JO.utf8
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ar_KW
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ar_KW.utf8
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ar_LB
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ar_LB.utf8
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ar_LY
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ar_LY.utf8
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ar_MA
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ar_MA.utf8
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ar_OM
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ar_OM.utf8
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ar_QA
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ar_QA.utf8
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ar_SA
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ar_SA.utf8
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ar_SD
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ar_SD.utf8
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ar_SY
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ar_SY.utf8
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ar_TN
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ar_TN.utf8
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ar_YE
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ar_YE.utf8
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be_BY
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be_BY.utf8
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bg_BG
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bg_BG.utf8
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br_FR
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bs_BA
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C
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ca_ES
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ca_ES@euro
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ca_ES.utf8
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ca_ES.utf8@euro
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cs_CZ
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cs_CZ.utf8
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cy_GB
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da_DK
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da_DK.iso885915
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da_DK.utf8
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de_AT
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de_AT@euro
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de_AT.utf8
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de_AT.utf8@euro
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de_BE
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de_BE@euro
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de_BE.utf8
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de_BE.utf8@euro
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de_CH
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de_CH.utf8
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de_DE
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de_DE@euro
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de_DE.utf8
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de_DE.utf8@euro
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de_LU
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de_LU@euro
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de_LU.utf8
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de_LU.utf8@euro
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el_GR
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el_GR.utf8
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en_AU
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en_AU.utf8
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en_BW
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en_BW.utf8
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en_CA
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en_CA.utf8
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en_DK
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en_DK.utf8
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en_GB
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en_GB.iso885915
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en_GB.utf8
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en_HK
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en_HK.utf8
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en_IE
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en_IE@euro
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en_IE.utf8
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en_IE.utf8@euro
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en_IN
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en_NZ
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en_NZ.utf8
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en_PH
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en_PH.utf8
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en_SG
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en_SG.utf8
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en_US
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en_US.iso885915
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en_US.utf8
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en_ZA
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en_ZA.utf8
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en_ZW
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en_ZW.utf8
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es_AR
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es_AR.utf8
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es_BO
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es_BO.utf8
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es_CL
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es_CL.utf8
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es_CO
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es_CO.utf8
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es_CR
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es_CR.utf8
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es_DO
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es_DO.utf8
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es_EC
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es_EC.utf8
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es_ES
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es_ES@euro
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es_ES.utf8
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es_ES.utf8@euro
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es_GT
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es_GT.utf8
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es_HN
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es_HN.utf8
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es_MX
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es_MX.utf8
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es_NI
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es_NI.utf8
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es_PA
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es_PA.utf8
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es_PE
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es_PE.utf8
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es_PR
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es_PR.utf8
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es_PY
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es_PY.utf8
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es_SV
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es_SV.utf8
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es_US
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es_US.utf8
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es_UY
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es_UY.utf8
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es_VE
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es_VE.utf8
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et_EE
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et_EE.utf8
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eu_ES
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eu_ES@euro
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eu_ES.utf8
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eu_ES.utf8@euro
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fa_IR
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fi_FI
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fi_FI@euro
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fi_FI.utf8
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fi_FI.utf8@euro
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fo_FO
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fo_FO.utf8
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fr_BE
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fr_BE@euro
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fr_BE.utf8
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fr_BE.utf8@euro
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fr_CA
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fr_CA.utf8
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fr_CH
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fr_CH.utf8
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fr_FR
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fr_FR@euro
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fr_FR.utf8
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fr_FR.utf8@euro
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fr_LU
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fr_LU@euro
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fr_LU.utf8
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fr_LU.utf8@euro
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ga_IE
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ga_IE@euro
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ga_IE.utf8
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ga_IE.utf8@euro
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gl_ES
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gl_ES@euro
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gl_ES.utf8
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gl_ES.utf8@euro
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gv_GB
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gv_GB.utf8
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he_IL
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he_IL.utf8
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hi_IN
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hr_HR
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hr_HR.utf8
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hu_HU
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hu_HU.utf8
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id_ID
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id_ID.utf8
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is_IS
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is_IS.utf8
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it_CH
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it_CH.utf8
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it_IT
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it_IT@euro
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it_IT.utf8
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it_IT.utf8@euro
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iw_IL
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iw_IL.utf8
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ja_JP.eucjp
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ja_JP.utf8
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ka_GE
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kl_GL
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kl_GL.utf8
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ko_KR.euckr
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ko_KR.utf8
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kw_GB
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kw_GB.utf8
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lt_LT
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lt_LT.utf8
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lv_LV
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lv_LV.utf8
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mi_NZ
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mk_MK
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mk_MK.utf8
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mr_IN
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ms_MY
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ms_MY.utf8
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mt_MT
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mt_MT.utf8
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nl_BE
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nl_BE@euro
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nl_BE.utf8
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nl_BE.utf8@euro
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nl_NL
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nl_NL@euro
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nl_NL.utf8
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nl_NL.utf8@euro
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nn_NO
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nn_NO.utf8
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no_NO
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no_NO.utf8
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oc_FR
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pl_PL
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pl_PL.utf8
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POSIX
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pt_BR
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pt_BR.utf8
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pt_PT
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pt_PT@euro
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pt_PT.utf8
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pt_PT.utf8@euro
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ro_RO
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ro_RO.utf8
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ru_RU
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ru_RU.koi8r
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ru_RU.utf8
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ru_UA
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ru_UA.utf8
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se_NO
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sk_SK
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sk_SK.utf8
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sl_SI
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sl_SI.utf8
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sq_AL
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sq_AL.utf8
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sr_YU
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sr_YU@cyrillic
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sr_YU.utf8
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sr_YU.utf8@cyrillic
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sv_FI
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sv_FI@euro
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sv_FI.utf8
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sv_FI.utf8@euro
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sv_SE
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sv_SE.iso885915
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sv_SE.utf8
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ta_IN
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te_IN
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tg_TJ
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th_TH
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th_TH.utf8
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tl_PH
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tr_TR
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tr_TR.utf8
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uk_UA
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uk_UA.utf8
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ur_PK
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uz_UZ
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vi_VN
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vi_VN.tcvn
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wa_BE
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wa_BE@euro
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yi_US
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zh_CN
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zh_CN.gb18030
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zh_CN.gbk
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zh_CN.utf8
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zh_HK
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zh_HK.utf8
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zh_TW
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zh_TW.euctw
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zh_TW.utf8
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</pre>
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</blockquote>
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</li>
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<li> <code>`locale`</code> displays environmental variables
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that impact how locale("") will be deduced.
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<blockquote>
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<pre>
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LANG=en_US
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LC_CTYPE="en_US"
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LC_NUMERIC="en_US"
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LC_TIME="en_US"
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LC_COLLATE="en_US"
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LC_MONETARY="en_US"
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LC_MESSAGES="en_US"
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LC_PAPER="en_US"
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LC_NAME="en_US"
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LC_ADDRESS="en_US"
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LC_TELEPHONE="en_US"
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LC_MEASUREMENT="en_US"
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LC_IDENTIFICATION="en_US"
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LC_ALL=
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</pre>
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</blockquote>
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</li>
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</ul>
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<p>
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From Josuttis, p. 697-698, which says, that "there is only *one*
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relation (of the C++ locale mechanism) to the C locale mechanism: the
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global C locale is modified if a named C++ locale object is set as the
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global locale" (emphasis Paolo), that is:
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</p>
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<code>std::locale::global(std::locale(""));</code>
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<p>affects the C functions as if the following call was made:</p>
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<code>std::setlocale(LC_ALL, "");</code>
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<p>
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On the other hand, there is *no* viceversa, that is, calling setlocale
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has *no* whatsoever on the C++ locale mechanism, in particular on the
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working of locale(""), which constructs the locale object from the
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environment of the running program, that is, in practice, the set of
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LC_ALL, LANG, etc. variable of the shell.
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</p>
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<h2>
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4. Design
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</h2>
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<p>
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The major design challenge is fitting an object-orientated and
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non-global locale design ontop of POSIX and other relevant stanards,
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which include the Single Unix (nee X/Open.)
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</p>
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<p>
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Because POSIX falls down so completely, portibility is an issue.
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</p>
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class _Impl
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The internal representation of the std::locale object.
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<h2>
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5. Examples
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</h2>
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More information can be found in the following testcases:
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<ul>
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<li> testsuite/22_locale/all </li>
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</ul>
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<h2>
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6. Unresolved Issues
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</h2>
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<ul>
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<li> locale initialization: at what point does _S_classic,
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_S_global get initialized? Can named locales assume this
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initialization has already taken place? </li>
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<li> document how named locales error check when filling data
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members. Ie, a fr_FR locale that doesn't have
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numpunct::truename(): does it use "true"? Or is it a blank
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string? What's the convention? </li>
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<li> explain how locale aliasing happens. When does "de_DE"
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use "de" information? What is the rule for locales composed of
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just an ISO language code (say, "de") and locales with both an
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ISO language code and ISO country code (say, "de_DE"). </li>
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<li> what should non-required facet instantiations do? If the
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generic implemenation is provided, then how to end-users
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provide specializations? </li>
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</ul>
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<h2>
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7. Acknowledgments
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</h2>
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<h2>
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8. Bibliography / Referenced Documents
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</h2>
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Drepper, Ulrich, GNU libc (glibc) 2.2 manual. In particular, Chapters "6. Character Set Handling" and "7 Locales and Internationalization"
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<p>
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Drepper, Ulrich, Numerous, late-night email correspondence
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</p>
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<p>
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ISO/IEC 14882:1998 Programming languages - C++
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</p>
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<p>
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ISO/IEC 9899:1999 Programming languages - C
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</p>
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<p>
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Langer, Angelika and Klaus Kreft, Standard C++ IOStreams and Locales, Advanced Programmer's Guide and Reference, Addison Wesley Longman, Inc. 2000
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</p>
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<p>
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Stroustrup, Bjarne, Appendix D, The C++ Programming Language, Special Edition, Addison Wesley, Inc. 2000
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</p>
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<p>
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System Interface Definitions, Issue 6 (IEEE Std. 1003.1-200x)
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The Open Group/The Institute of Electrical and Electronics Engineers, Inc.
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http://www.opennc.org/austin/docreg.html
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</p>
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</body>
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</html>
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