<!-- cribtutor-stl by NewForester is licensed under a Creative Commons Attribution-ShareAlike 4.0 International Licence. -->

<h1> Other STL Containers </h1>

<h2> Locale </h2>

<p>

Localisation is about internationalisation.

It is about producing software (applications) for use around the world.

</p>

<p>

This crib-sheet is an <em>overview</em> of the C++ locale facilities:

it does not cover all the complexities of this subject.

</p>

<!--

The author of this crib sheet has limited experience of internationalisation

and even less of localisation in C/C++.

Describing the C++ localisation when the concepts are only understood

in abstract terms has not been easy.

-->

<h3> Introduction </h3>

<p>

A <em>locale</em> is a set of parameters that define

the user&apos;s language, alphabet (character set), country and regional preferences.

Software applications use these <em>parameters</em> to adapt their handling of input and output.

</p>

<p>

locale identifiers are subject to international standardisation

but locale implementation is <em>platform</em> specific

(i.e. Microsoft does not use POSIX locales and Linux does not use Windows locales).

</p>

<p>

On <em>POSIX</em> platforms locale identifiers are defined by ISO 15897.

Their format is:

<pre>

[language[_territory][.codeset][@modifier]].

</pre>

</p>

<p />

<p>

C localisation is available in the header file &lt;<em>clocale</em>&gt;.

It provides 13 categories of locale parameters that may be set independently

but only one <em>global</em> locale.

</p>

<p>

C++ localisation is provided in the &lt;<em>locale</em>&gt; header file.

locale <em>objects</em> provide support for the 6 most important parameter categories through <em>facets</em>.

</p>

<p>

These cover:

<ol><!-- Shuffle List -->

<li> <em>formatting</em> of date/time, numeric and monetary values </li>

<li> <em>character</em> classification and conversion </li>

<li> string <em>collation</em> </li>

<li> <em>message</em> retrieval </li>

</ol>

</p>

<p>

Localisation is not <em>automatic</em>:

applications are designed and implemented with localisation in mind.

The amount of work needed depends on the degree of customisation required.

</p>

<p>

Some aspects of locale specific input and output can be a handled automatically.

In particular character set <em>conversion</em>.

</p>

<p>

In the past this meant conversion

to/from the system <em>code page</em> on output/input.

Today this generally means conversion to/from <em>Unicode</em>.

That is UTF-8 on POSIX systems and UTF-16 on Windows systems.

</p>

<p>

The <em>global</em> nature of the C locale means it affects all input and output.

The <em>object oriented</em> nature of C++ locales means that

a locale can be i/o stream specific: the locale is <em>imbued</em> in the stream.

</p>

<p>

<em>Formatting</em> manipulators, methods and flags alter how numeric values

are input and output in C++.

When imbued with a locale, their effects are altered, sometimes subtly.

</p>

<p>

Not all aspects of the locale can be handled automatically and not all aspects of input/output are stream related

(consider field based GUI/web forms).

Typcially, the details of application specific locale handling

will be <em>encapsulated</em> in custom insertion/extraction <em>operators</em>.

</p>

<p>

Since locale handling is intimately connected with stream handling,

the locale methods have <em>intricate</em> calling sequences.

</p>

<p>

The STL does not provide support for all aspects of a locale

(for example paper size)

but the locale may be customised by <em>extension</em> and <em>overlay</em>.

</p>

<p />

<p>

C/C++ provide the &apos;char&apos; and &apos;wchar_t&apos;

(aka narrow and wide character) types.

The first is generally adequate for <em>phonetic</em> alphabets

used by languages such as English and Russian

but the second is needed for <em>logographic</em> alphabets

used by languages such as Chinese and Japanese.

</p>

<p>

STL locale handling uses templates and provides support for both

<em>narrow</em> and <em>wide</em> character types.

With C++ 11 the &apos;char16_t&apos; and &apos;char32_t&apos;

provide additional support for Unicode.

</p>

<p>

Every locale object provides locale specific template <em>specialisations</em>.

The STL also provides <em>standalone</em>, locale independent,

template specialisations

that generally correspond to the default &quot;C&quot; locale.

</p>

<p>

The rest of this crib-sheet leaves out such <em>details</em> for the sake of clarity.

</p>

<h3> The locale Class </h3>

<p>

Localisation is provided by the <em>locale</em> class.

This may be thought of as a container for <em>facet</em>&lt;&gt; objects.

The locale knows nothing of the capabilities of its facets.

It does not provide internationalisation services itself.

</p>

<p>

The locale contains six (standard) facet&lt;&gt; objects for

six categories of localisation.

<ol><!-- Shuffle List -->

<li> <em>LC_NUMERIC</em> - rules and symbols for number formatting </li>

<li> <em>LC_MONETARY</em> - rules and symbols for monetary information </li>

<li> <em>LC_TIME</em> - values for date and time information </li>

<li> <em>LC_CTYPE</em> - character classification and case conversion </li>

<li> <em>LC_COLLATE</em> - character collation sequences </li>

<li> <em>LC_MESSAGES</em> - formats and values of messages </li>

</ol>

In general, each category is implemented by more than one facet object.

</p>

<p>

The locale container design allows <em>custom</em> facets,

which can either be in addition to or instead of the standard facets.

</p>

<p>

The design also allows the same facet&lt;&gt; <em>objects</em> to be used

in different <em>locales</em>.

They can be retrieved and copied efficiently.

</p>

<p>

Standard locales are constructed by <em>name</em>:

<pre>

locale(&quot;De_DE&quot;);

</pre>

Names are those of C locales.

</p>

<p>

The name of C locales are <em>platform</em> dependent.

At a very minimum, the system default locale <em>&quot;&quot;</em> and

the minimal <em>&quot;C&quot;</em> locale are defined.

</p>

<p>

<em>Custom</em> locales are constructed by <em>composition</em>:

<pre>

locale here (locale::classic(), locale(&quot;De_DE&quot;), LC_NUMERIC);

</pre>

where

<pre>

locale::classic();

</pre>

returns the equivalent of the &quot;C&quot; locale

(which corresponds more or less to US English ASCII).

</p>

<p>

Once constructed, locale objects are <em>immutable</em>.

Copy operations are <em>cheap</em> (handle-body-idiom).

</p>

<p>

There are two template functions that operate on locale objects:

<ol><!-- Shuffle List -->

<li> <em>use_facet</em>() - retrieve a facet from a locale </li>

<li> <em>has_facet</em>() - test whether a locale has a facet </li>

</ol>

</p>

<p>

Since locales are constructed by composition,

they all contain the facets defined in the standard:

<em>has_facet</em>() is only needed when using additional <em>custom</em> facets.

</p>

<p>

Which facet is retrieved by <em>use_facet</em>() is specified

by template <em>instantiation</em> and not by parameter:

<pre>

const numpunct&lt; char &gt;&amp; myfacet = use_facet &lt; numpunct&lt; char &gt; &gt; (mylocale);

myvar = myfacet.decimal_point();

</pre>

</p>

<p>

Assume the <em>reference</em> to a facet is valid until the locale object is <em>destroyed</em>.

</p>

<p>

The method:

<ol><!-- Shuffle List -->

<li> locale::<em>global</em>() </li>

</ol>

may be used to set the global C++ locale.

This also affects the C locale and may <em>break</em> third party packages

that are not locale aware.

</p>

<h3> Use of locale Objects </h3>

<p>

A locale may be <em>imbued</em> in an i/o stream as follows:

<pre>

cout.imbue(locale(&quot;ru_RU.UTF-8&quot;));

</pre>

</p>

<p>

This may affect:

<ol><!-- Shuffle List -->

<li> character set <em>conversion</em> at a low level </li>

<li> <em>number</em> insertion and extraction </li>

<li> white space recognition during <em>extraction</em> </li>

</ol>

For example:

<pre>

// This will output 1.234.567,89 ...

double n = 1234567.89;

cout.imbue(std::locale(&quot;de_DE&quot;));

cout &lt;&lt; std::fixed &lt;&lt; n &lt;&lt; endl;

// ... and this will read it back in

istringstream de_in(&quot;1.234.567,89&quot;);

de_in.imbue(locale(&quot;de_DE&quot;));

double f1;

de_in &gt;&gt; f1;

</pre>

</p>

<h3> facet Class Templates </h3>

<p>

The standard facets are:

<ol><!-- Shuffle List -->

<li> <em>time_get</em>&lt;&gt; parses time/date values from an input character sequence into struct std::tm </li>

<li> <em>time_put</em>&lt;&gt; formats contents of struct std::tm for output as a character sequence </li>

<li> <em>num_get</em>&lt;&gt; parses numeric values from an input character sequence </li>

<li> <em>num_put</em>&lt;&gt; formats numeric values for output as a character sequence </li>

<li> <em>numpunct</em>&lt;&gt; defines punctuation characters and formatting rules for numeric values </li>

<li> <em>money_get</em>&lt;&gt; parses a monetary value from an input character sequence </li>

<li> <em>money_put</em>&lt;&gt; formats a monetary value for output as a character sequence </li>

<li> <em>moneypunct</em>&lt;&gt; defines punctuation characters and formatting rules for monetary values </li>

<li> <em>ctype</em>&lt;&gt; defines character classification tables and provides helper routines </li>

<li> <em>collate</em>&lt;&gt; defines lexicographical comparison and hashing of strings </li>

<li> <em>messages</em>&lt;&gt; implements retrieval of strings from message catalogues </li>

<li> <em>codecvt</em>&lt;&gt; converts between external and internal character encodings </li>

</ol>

All have a common base class std::locale::facet&lt;&gt;.

</p>

<p>

For codecvt&lt;&gt; the first two template parameters are character types.

For all other facets, the first template parameter is a character type.

The STL provides specialisations for <em>char</em> and <em>wchar_t</em>.

</p>

<!--

Support for &apos;char16_t&apos; and &apos;char32_t&apos; is provided by the codecvt facet from C++ 11 onwards.

-->

<p>

The twelve facet templates above are to be used with use_facet() to retrieve facet objects from a locale object.

They define abstract interface classes with no implementation.

However, use_facet() returns references to concrete implementations instantiated using the constructor for:

<ol><!-- Shuffle List -->

<li> <em>numpunct_byname</em> instantiation of numpunct for a named locale </li>

<li> <em>moneypunct_byname</em> instantiation of moneypunct for a named locale </li>

<li> <em>time_get_byname</em> instantiation of time_get for a named locale </li>

<li> <em>time_put_byname</em> instantiation of time_put for a named locale </li>

<li> <em>ctype_byname</em> instantiation of ctype for a named locale </li>

<li> <em>collate_byname</em> instantiation of collate for a named locale </li>

<li> <em>messages_byname</em> instantiation of messages for a named locale </li>

<li> <em>codecvt_byname</em> instantiation of codecvt for a named locale </li>

</ol>

Their constructors are only of interest when constructing special purpose locale objects.

</p>

<h3> Character Conversion </h3>

<p>

The codecvt facet of the <em>LC_CTYPE</em> category encapsulates character set conversion.

Specifically between some <em>external</em> character encoding and the corresponding C++ internal &apos;narrow&apos; or &apos;wide&apos; character representation.

</p>

<p>

The <em>wide</em> character representations of a character requires one (typically 4 byte) wchar_t position;

The <em>narrow</em> character representations requires one or more char positions.

</p>

<p>

<em>Multi-byte</em> characters are <em>narrow</em> characters that requires more than one char position.

Variable byte encoding and state machine encoding are the two approaches used for multi-byte encoding.

</p>

<p>

The methods provided by the codecvt facet are:

<ol><!-- Shuffle List -->

<li> codecvt.<em>in</em>() convert a string from external to internal representation, such as when reading from file </li>

<li> codecvt.<em>out</em>() convert a string from internal to external representation, such as when writing to file </li>

<li> codecvt.<em>unshift</em>() generate the necessary state machine termination sequence for incomplete conversion to the external representation </li>

<li> codecvt.<em>always_noconv</em>() true if the conversion is the identity (i.e. no conversion required) </li>

<li> codecvt.<em>encoding</em>() the number of external characters needed to produce one internal character (if constant) </li>

<li> codecvt.<em>length</em>() the number of external characters that would be consumed by conversion into a given number of internal characters </li>

<li> codecvt.<em>max_length</em>() the maximum number of external characters that may be generated by the conversion of a single internal character </li>

</ol>

</p>

<p>

codecvt.encoding() returns 0 for a <em>variable byte</em> encoding and -1 for a <em>state machine</em> encoding.

</p>

<!--

C++ 11 appears to add support for Unicode as external representations and also,

through the template conversion classes wstring_convert and wbuffer_convert,

the use of Unicode as internal representations.

-->

<h3> Message Retrieval </h3>

<p>

The <em>LC_MESSAGES</em> category has a single facet that encapsulates the retrieval of strings from message catalogues.

Message catalogues support the lookup of locale specific <em>translations</em> of user interface text (such as error messages).

</p>

<p>

The <em>message</em> facet delegates to platform specific routines:

on GNU/Linux systems, message catalogues are provided by GNU <em>gettext</em> and on POSIX systems by <em>catgets</em>.

</p>

<p>

The methods provided by the message facet are:

<ol><!-- Shuffle List -->

<li> message.<em>open</em>() open a named message catalogue </li>

<li> message.<em>get</em>() retrieve a message from an open message catalogue </li>

<li> message.<em>close</em>() close a message catalogue </li>

</ol>

</p>

<p>

message.open() takes as parameters the <em>catalogue</em> name and a <em>locale</em> object.

It returns a <em>handle</em> of type catalogue that can then be used with message.get() and message.close().

</p>

<p>

The <em>catalogue</em> name is just that (probably the name of the program/application).

The file system location of catalogues is <em>platform</em> specific.

</p>

<p>

If the catalogue could not be opened the handle has a <em>negative</em> value.

Otherwise, the handle remains valid until passed to message.close().

</p>

<p>

message.close() <em>releases</em> any resources allocated to an open catalogue.

</p>

<p>

message.get() is passed <em>text</em> to translate

and returns the <em>translation</em> found in the catalogue or else a copy of the original text.

</p>

<p>

message.get() also takes two <em>platform</em> specific parameters.

On POSIX systems identify the message to be retrieved.

On GNU libstdc++ systems these parameters are <em>ignored</em> and the text is used (as a hash key ?).

</p>

<h3> String Collation </h3>

<p>

The <em>LC_COLLATE</em> category has a single facet that encapsulates locale specific string collation (comparison) and string hashing.

</p>

<p>

Collation order (as opposed to lexicographical order) is <em>dictionary</em> order:

<ol><!-- Shuffle List -->

<li> position within the alphabet takes <em>precedence</em> over case </li>

<li> lowercase <em>collates</em> before uppercase </li>

<li> locale specific order may apply to <em>diacriticals</em> </li>

<li> groups of characters may <em>compare</em> as a single collation unit </li>

</ol>

For example, in Czech &apos;ch&apos; follows &apos;h&apos; and precedes &apos;i&apos;,

while Hungarian &apos;dzs&apos; follows &apos;dz&apos; and precedes &apos;g&apos;.

</p>

<p>

The methods provided by the collate facet are:

<ol><!-- Shuffle List -->

<li> collate.<em>compare</em>() compare two strings using dictionary order </li>

<li> collate.<em>transform</em>() transform a string so that collation can be replaced by comparison </li>

<li> collate.<em>hash</em>() generate an integer hash value using collation rules </li>

</ol>

</p>

<p>

collate.compare() compares two character <em>sequences</em> using locale collation rules.

The return value is as for <em>strcmp</em>()

with 0 indicating the two sequences are <em>equivalent</em>.

</p>

<p>

collate.transform() converts a character sequence so that

<em>operator&lt;</em> will yield the same results on transformed strings as

collate.compare() does on the original strings (but is generally faster).

</p>

<p>

collate.hash() converts a character sequence to an <em>integer</em> hash value such that all strings that collate.compare() would consider equivalent have the same hash value

and the <em>probability</em> of two strings otherwise having the same hash value is very small.

</p>

<p>

When a locale object is passed as a comparator to an STL <em>algorithm</em>,

the locale&apos;s collate.compare() function is invoked to perform the actual comparison.

True is returned if the two strings are equivalent:

<pre>

sort(v.begin(), v.end(), locale(&quot;sv_SE.UTF-8&quot;));

</pre>

</p>

<!-- The collate facet is used by std::basic_regex in C++ 11 and later. -->

<h3> Character Classification </h3>

<p>

The ctype facet of the <em>LC_CTYPE</em> category encapsulates character classification and conversion.

</p>

<p>

The methods provided by the ctype facet are:

<ol><!-- Shuffle List -->

<li> ctype.<em>is</em>() classify a character or a character sequence </li>

<li> ctype.<em>scan_is</em>() locate the first character in a sequence that conforms to the given classification </li>

<li> ctype.<em>scan_not</em>() locate the first character in a sequence that does not conform to the given classification </li>

<li> ctype.<em>toupper</em>() convert a character or characters to uppercase </li>

<li> ctype.<em>tolower</em>() convert a character or characters to lowercase </li>

<li> ctype.<em>widen</em>() convert a character or characters from char to &apos;charT&apos; </li>

<li> ctype.<em>narrow</em>() convert a character or characters from &apos;charT&apos; to char </li>

</ol>

</p>

<p>

ctype.is() has two forms.

The first takes a mask and a character as input and returns a <em>bool</em> to indicate a match.

The second takes a character <em>sequence</em> as input and returns a (character) sequence of masks.

</p>

<p>

ctype.scan_is()/ctype.scan_not() take a character <em>sequence</em> and return a <em>pointer</em> to the first matching/non-matching character.

</p>

<p>

The other methods return the <em>converted</em> character when passed a single character.

Alternatively they are passed two character <em>sequences</em>.

</p>

<p>

ctype.toupper()/ctype.tolower() convert characters <em>in-place</em> whereas

ctype.widen()/ctype.narrow() take a pointer to a <em>destination</em> sequence.

</p>

<h3> Formatting of Numeric Values </h3>

<p>

The <em>LC_NUMERIC</em> facets encapsulate conversion between external character representations of numeric values and C++ numeric types.

</p>

<p>

The methods provided by these facets are:

<ol><!-- Shuffle List -->

<li> num_put.<em>put</em>() format a C++ numeric value for output as a character sequence </li>

<li> num_get.<em>get</em>() parse a character sequence producing a numeric value </li>

<li> numpunct.<em>decimal_point</em>() return the &apos;decimal point&apos; character </li>

<li> numpunct.<em>thousands_sep</em>() return the &apos;thousands separator&apos; character </li>

<li> numpunct.<em>grouping</em>() return the numbers of digits between pairs of &apos;thousand separators&apos; </li>

<li> numpunct.<em>falsename</em>() return the locale language representation of &apos;false&apos; </li>

<li> numpunct.<em>truename</em>() return the locale language representation of &apos;true&apos; </li>

</ol>

</p>

<p>

The thousand separator is a <em>C-string</em> of char values.

The simplest locale is &quot;\3&quot;, which means every <em>third</em> position.

The Nepalese locale uses &quot;\3\2&quot;, which means the third position and then every second position moving right to left.

</p>

<p>

The default locale uses &apos;.&apos; as <em>decimal point</em> and &apos;,&apos; as <em>thousands separator</em>.

However, the grouping of thousand separator is an empty string, which means <em>no</em> separators.

</p>

<h3> Formatting of Monetary Values </h3>

<p>

The <em>LC_MONETARY</em> facets encapsulate conversion between external character representations of monetary values and either C++ long double or string types.

</p>

<p>

The internal representations assume the locale&apos;s smallest <em>non-fractional</em> currency units. E.g. yen in Japan but cents (not) Euros in Europe.

</p>

<p>

The methods provided by these facets are:

<ol><!-- Shuffle List -->

<li> money_put.<em>put</em>() format a C++ numeric value for output as a character sequence </li>

<li> money_get.<em>get</em>() parse a character sequence producing a numeric value </li>

<li> moneypunct.<em>decimal_point</em>() return the &apos;decimal point&apos; character </li>

<li> moneypunct.<em>thousands_sep</em>() return the &apos;thousands&apos; separator character </li>

<li> moneypunct.<em>grouping</em>() return the numbers of digits between pairs of &apos;thousand&apos; separators </li>

<li> moneypunct.<em>frac_digits</em>() return the number of digits to display after the decimal point (e.g. 2) </li>

<li> moneypunct.<em>curr_symbol</em>() return the string to use as the currency identifier </li>

<li> moneypunct.<em>positive_sign</em>() return the string to indicate a positive value </li>

<li> moneypunct.<em>negative_sign</em>() return the string to indicate a negative value </li>

<li> moneypunct.<em>pos_format</em>() return the formatting pattern for positive currency values </li>

<li> moneypunct.<em>neg_format</em>() return the formatting pattern for negative currency values </li>

</ol>

</p>

<p>

The currency symbol is a string: either a (usually) <em>single</em> character (e.g. &quot;€&quot;) or the 3 letter <em>international</em> code followed by a space (e.g &quot;EUR &quot;).

A <em>bool</em> parameter to put()/get()/curr_symbol() determines which.

The std::showbase affects the presence of the currency symbol for currency values very much the way is affects the presence of 0x for hexadecimal values.

</p>

<p>

The positive and negative signs are strings.

If either is more than one character, all but the <em>first</em> appear at the <em>end</em> of the formatted currency value so that &quot;()&quot; gives what is wanted.

The std::showpos has no affect on the presence of the positive sign.

</p>

<p>

The positive and negative formats are each an <em>array</em> of four enumeration values.

The locale independent default is &apos;{symbol, sign, none, value}&apos;.

</p>

<p>

<em>C++ 11</em> introduces the i/o stream manipulators:

<ol><!-- Shuffle List -->

<li> put_money() </li>

<li> get_money() </li>

</ol>

that mean that application software generally need not use these facets directly.

</p>

<h3> Formatting of Date and Time Values</h3>

<p>

The <em>LC_TIME</em> facets encapsulate conversion between external character representations and std::tm (C-style &apos;struct tm&apos;) objects.

Conversion is derived from that of the C-function strftime().

</p>

<p>

The methods provided by these facets are:

<ol><!-- Shuffle List -->

<li> time_put.<em>put</em>() format contents of a std::tm struct for output as a character sequence </li>

<li> time_get.<em>get</em>() parse a character sequence producing a std::tm struct result </li>

<li> time_get.<em>get_time</em>() parse a character sequence representing a time </li>

<li> time_get.<em>get_date</em>() parse a character sequence representing a date </li>

<li> time_get.<em>get_weekday</em>() parse a character sequence representing the name of a weekday </li>

<li> time_get.<em>get_monthname</em>() parse a character sequence representing the name of a month </li>

<li> time_get.<em>get_year</em>() parse a character sequence representing a year number </li>

<li> time_get.<em>date_order</em>() get the enumeration value representing the date format (day, month, year permutation) </li>

</ol>

</p>

<p>

The put() function has two forms:

the format specifier is either a <em>single</em> character representing one of the strftime() format specifiers

or else a <em>C-string</em> suitable for passing to strftime().

</p>

<p>

The get() function is the inverse of put().

It was introduced with <em>C++ 11</em>.

</p>

<p>

The other methods only set <em>pertinent</em> members of the std::tm struct - other members are unchanged.

</p>

<p>

The get_time() and get_date() conversions are the <em>inverse</em> of the strftime() &quot;%X&quot; and &quot;%x&quot; formats.

It must be presumed that the time and date punctuation is locale dependent; the date order certainly is.

</p>

<p>

Abbreviated names of <em>weekdays</em> and <em>months</em> are recognised as well as the full versions.

They are locale language specific.

</p>

<p>

It is not specified whether <em>two digit</em> year numbers are accepted nor in which century they lie.

</p>

<h3> Template Functions </h3>

<p>

A number of template functions are provided that are <em>analogous</em> to familiar C functions.

These take, as a <em>second</em> parameter, a locale object, instead of using the (global) C locale.

</p>

<p>

An example <em>implementation</em> might be:

<pre>

template&lt; class charT &gt;

bool isspace(charT ch, const locale&amp; loc)

{

return use_facet&lt; ctype&lt;charT&gt; &gt;(loc).is(ctype_base::space, ch);

}

</pre>

</p>

<p>

There are a dozen template functions for character classification:

<ol><!-- Shuffle List -->

<li> <em>isspace</em>() true if a character is a locale defined whitespace </li>

<li> <em>isblank</em>() true if a character is a locale defined blank character </li>

<li> <em>iscntrl</em>() true if a character is a locale defined control character </li>

<li> <em>isupper</em>() true if a character is a locale defined uppercase </li>

<li> <em>islower</em>() true if a character is a locale defined lowercase </li>

<li> <em>isalpha</em>() true if a character is a locale defined alphabetic </li>

<li> <em>isdigit</em>() true if a character is a locale defined digit </li>

<li> <em>ispunct</em>() true if a character is a locale defined punctuation </li>

<li> <em>isxdigit</em>() true if a character is a locale defined hexadecimal digit </li>

<li> <em>isalnum</em>() true if a character is a locale defined alphanumeric </li>

<li> <em>isprint</em>() true if a character is a locale defined printable </li>

<li> <em>isgraph</em>() true if a character is a locale defined graphical </li>

</ol>

</p>

<p>

isblank() was new with <em>C++ 11</em>.

</p>

<p>

There are two template functions for character conversion:

<ol><!-- Shuffle List -->

<li> <em>toupper</em>() convert a character to locale uppercase </li>

<li> <em>tolower</em>() convert a character to locale lowercase </li>

</ol>

</p>

<h3> Problems </h3>

<p>

Setting the <em>global</em> C++ locale may have bad side effects.

Many packages are not locale aware and may be broken.

</p>

<p>

Locale names are <em>platform</em> specific as is their availability.

UTF-8 is not supported on Windows.

</p>

<p>

On some platforms the STL supports only the &quot;C&quot; and &quot;POSIX&quot; locales.

GCC supports localisation only under <em>Linux</em>.

</p>

<p>

Some locales use a <em>non-breakable</em> space as a thousands separator.

Not all platforms handle this correctly.

</p>