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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<meta name="AUTHOR" content="bkoz@redhat.com (Benjamin Kosnik)" />
<meta name="KEYWORDS" content="HOWTO, libstdc++, locale name LC_ALL" />
<meta name="DESCRIPTION" content="Notes on the locale implementation." />
<title>Notes on the locale implementation.</title>
<link rel="StyleSheet" href="../lib3styles.css" />
</head>
<body>
<h1>
Notes on the locale implementation.
</h1>
<em>
prepared by Benjamin Kosnik (bkoz@redhat.com) on October 14, 2002
</em>
<h2>
1. Abstract
</h2>
<p>
Describes the basic locale object, including nested
classes id, facet, and the reference-counted implementation object,
class _Impl.
</p>
<h2>
2. What the standard says
</h2>
Class locale is non-templatized and has two distinct types nested
inside of it:
<blockquote>
<em>
class facet
22.1.1.1.2 Class locale::facet
</em>
</blockquote>
<p>
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.
</p>
Literally, a facet is strictly defined:
<ul>
<li>containing the following public data member:
<p>
<code>static locale::id id;</code>
</p>
</li>
<li>derived from another facet:
<p>
<code> class gnu_codecvt: public std::ctype<user-defined-type></code>
</p>
</li>
</ul>
<p>
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.
</p>
<blockquote>
<em>
class id
22.1.1.1.3 - Class locale::id
</em>
</blockquote>
<p>
Provides an index for looking up specific facets.
<p>
<h2>
3. Interacting with "C" locales.
</h2>
<p>
Some help on determining the underlying support for locales on a system.
Note, this is specific to linux (and glibc-2.3.x)
</p>
<ul>
<li> <code>`locale -a`</code> displays available locales.
<blockquote>
<pre>
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
</pre>
</blockquote>
</li>
<li> <code>`locale`</code> displays environmental variables
that impact how locale("") will be deduced.
<blockquote>
<pre>
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=
</pre>
</blockquote>
</li>
</ul>
<p>
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:
</p>
<code>std::locale::global(std::locale(""));</code>
<p>affects the C functions as if the following call was made:</p>
<code>std::setlocale(LC_ALL, "");</code>
<p>
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.
</p>
<h2>
4. Design
</h2>
<p>
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.)
</p>
<p>
Because POSIX falls down so completely, portibility is an issue.
</p>
class _Impl
The internal representation of the std::locale object.
<h2>
5. Examples
</h2>
More information can be found in the following testcases:
<ul>
<li> testsuite/22_locale/all </li>
</ul>
<h2>
6. Unresolved Issues
</h2>
<ul>
<li> locale initialization: at what point does _S_classic,
_S_global get initialized? Can named locales assume this
initialization has already taken place? </li>
<li> 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? </li>
<li> 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"). </li>
<li> what should non-required facet instantiations do? If the
generic implemenation is provided, then how to end-users
provide specializations? </li>
</ul>
<h2>
7. Acknowledgments
</h2>
<h2>
8. Bibliography / Referenced Documents
</h2>
Drepper, Ulrich, GNU libc (glibc) 2.2 manual. In particular, Chapters "6. Character Set Handling" and "7 Locales and Internationalization"
<p>
Drepper, Ulrich, Numerous, late-night email correspondence
</p>
<p>
ISO/IEC 14882:1998 Programming languages - C++
</p>
<p>
ISO/IEC 9899:1999 Programming languages - C
</p>
<p>
Langer, Angelika and Klaus Kreft, Standard C++ IOStreams and Locales, Advanced Programmer's Guide and Reference, Addison Wesley Longman, Inc. 2000
</p>
<p>
Stroustrup, Bjarne, Appendix D, The C++ Programming Language, Special Edition, Addison Wesley, Inc. 2000
</p>
<p>
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
</p>
</body>
</html>
|
