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| |
| <h3 class="section">4.3 Character class determination for wide characters</h3> |
| |
| <p>Amendment 1<!-- /@w --> to ISO C90<!-- /@w --> defines functions to classify wide |
| characters. Although the original ISO C90<!-- /@w --> standard already defined |
| the type <code>wchar_t</code>, no functions operating on them were defined. |
| |
| <p>The general design of the classification functions for wide characters |
| is more general. It allows extensions to the set of available |
| classifications, beyond those which are always available. The POSIX |
| standard specifies how extensions can be made, and this is already |
| implemented in the GNU C library implementation of the <code>localedef</code> |
| program. |
| |
| <p>The character class functions are normally implemented with bitsets, |
| with a bitset per character. For a given character, the appropriate |
| bitset is read from a table and a test is performed as to whether a |
| certain bit is set. Which bit is tested for is determined by the |
| class. |
| |
| <p>For the wide character classification functions this is made visible. |
| There is a type classification type defined, a function to retrieve this |
| value for a given class, and a function to test whether a given |
| character is in this class, using the classification value. On top of |
| this the normal character classification functions as used for |
| <code>char</code> objects can be defined. |
| |
| <!-- wctype.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Data type: <b>wctype_t</b><var><a name="index-wctype_005ft-405"></a></var><br> |
| <blockquote><p>The <code>wctype_t</code> can hold a value which represents a character class. |
| The only defined way to generate such a value is by using the |
| <code>wctype</code> function. |
| |
| <p><a name="index-wctype_002eh-406"></a>This type is defined in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <!-- wctype.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: wctype_t <b>wctype</b> (<var>const char *property</var>)<var><a name="index-wctype-407"></a></var><br> |
| <blockquote><p>The <code>wctype</code> returns a value representing a class of wide |
| characters which is identified by the string <var>property</var>. Beside |
| some standard properties each locale can define its own ones. In case |
| no property with the given name is known for the current locale |
| selected for the <code>LC_CTYPE</code> category, the function returns zero. |
| |
| <p class="noindent">The properties known in every locale are: |
| |
| <p><table summary=""><tr align="left"><td valign="top" width="25%"><code>"alnum"</code> </td><td valign="top" width="25%"><code>"alpha"</code> </td><td valign="top" width="25%"><code>"cntrl"</code> </td><td valign="top" width="25%"><code>"digit"</code> |
| <br></td></tr><tr align="left"><td valign="top" width="25%"><code>"graph"</code> </td><td valign="top" width="25%"><code>"lower"</code> </td><td valign="top" width="25%"><code>"print"</code> </td><td valign="top" width="25%"><code>"punct"</code> |
| <br></td></tr><tr align="left"><td valign="top" width="25%"><code>"space"</code> </td><td valign="top" width="25%"><code>"upper"</code> </td><td valign="top" width="25%"><code>"xdigit"</code> |
| <br></td></tr></table> |
| |
| <p><a name="index-wctype_002eh-408"></a>This function is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p>To test the membership of a character to one of the non-standard classes |
| the ISO C<!-- /@w --> standard defines a completely new function. |
| |
| <!-- wctype.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: int <b>iswctype</b> (<var>wint_t wc, wctype_t desc</var>)<var><a name="index-iswctype-409"></a></var><br> |
| <blockquote><p>This function returns a nonzero value if <var>wc</var> is in the character |
| class specified by <var>desc</var>. <var>desc</var> must previously be returned |
| by a successful call to <code>wctype</code>. |
| |
| <p><a name="index-wctype_002eh-410"></a>This function is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p>To make it easier to use the commonly-used classification functions, |
| they are defined in the C library. There is no need to use |
| <code>wctype</code> if the property string is one of the known character |
| classes. In some situations it is desirable to construct the property |
| strings, and then it is important that <code>wctype</code> can also handle the |
| standard classes. |
| |
| <p><a name="index-alphanumeric-character-411"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswalnum</b> (<var>wint_t wc</var>)<var><a name="index-iswalnum-412"></a></var><br> |
| <blockquote><p>This function returns a nonzero value if <var>wc</var> is an alphanumeric |
| character (a letter or number); in other words, if either <code>iswalpha</code> |
| or <code>iswdigit</code> is true of a character, then <code>iswalnum</code> is also |
| true. |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("alnum")) |
| </pre> |
| <p><a name="index-wctype_002eh-413"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-alphabetic-character-414"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswalpha</b> (<var>wint_t wc</var>)<var><a name="index-iswalpha-415"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is an alphabetic character (a letter). If |
| <code>iswlower</code> or <code>iswupper</code> is true of a character, then |
| <code>iswalpha</code> is also true. |
| |
| <p>In some locales, there may be additional characters for which |
| <code>iswalpha</code> is true—letters which are neither upper case nor lower |
| case. But in the standard <code>"C"</code> locale, there are no such |
| additional characters. |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("alpha")) |
| </pre> |
| <p><a name="index-wctype_002eh-416"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-control-character-417"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswcntrl</b> (<var>wint_t wc</var>)<var><a name="index-iswcntrl-418"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a control character (that is, a character that |
| is not a printing character). |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("cntrl")) |
| </pre> |
| <p><a name="index-wctype_002eh-419"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-digit-character-420"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswdigit</b> (<var>wint_t wc</var>)<var><a name="index-iswdigit-421"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a digit (e.g., ‘<samp><span class="samp">0</span></samp>’ through ‘<samp><span class="samp">9</span></samp>’). |
| Please note that this function does not only return a nonzero value for |
| <em>decimal</em> digits, but for all kinds of digits. A consequence is |
| that code like the following will <strong>not</strong> work unconditionally for |
| wide characters: |
| |
| <pre class="smallexample"> n = 0; |
| while (iswdigit (*wc)) |
| { |
| n *= 10; |
| n += *wc++ - L'0'; |
| } |
| </pre> |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("digit")) |
| </pre> |
| <p><a name="index-wctype_002eh-422"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-graphic-character-423"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswgraph</b> (<var>wint_t wc</var>)<var><a name="index-iswgraph-424"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a graphic character; that is, a character |
| that has a glyph associated with it. The whitespace characters are not |
| considered graphic. |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("graph")) |
| </pre> |
| <p><a name="index-wctype_002eh-425"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-lower_002dcase-character-426"></a><!-- ctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswlower</b> (<var>wint_t wc</var>)<var><a name="index-iswlower-427"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a lower-case letter. The letter need not be |
| from the Latin alphabet, any alphabet representable is valid. |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("lower")) |
| </pre> |
| <p><a name="index-wctype_002eh-428"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-printing-character-429"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswprint</b> (<var>wint_t wc</var>)<var><a name="index-iswprint-430"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a printing character. Printing characters |
| include all the graphic characters, plus the space (‘<samp> </samp>’) character. |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("print")) |
| </pre> |
| <p><a name="index-wctype_002eh-431"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-punctuation-character-432"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswpunct</b> (<var>wint_t wc</var>)<var><a name="index-iswpunct-433"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a punctuation character. |
| This means any printing character that is not alphanumeric or a space |
| character. |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("punct")) |
| </pre> |
| <p><a name="index-wctype_002eh-434"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-whitespace-character-435"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswspace</b> (<var>wint_t wc</var>)<var><a name="index-iswspace-436"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a <dfn>whitespace</dfn> character. In the standard |
| <code>"C"</code> locale, <code>iswspace</code> returns true for only the standard |
| whitespace characters: |
| |
| <dl> |
| <dt><code>L' '</code><dd>space |
| |
| <br><dt><code>L'\f'</code><dd>formfeed |
| |
| <br><dt><code>L'\n'</code><dd>newline |
| |
| <br><dt><code>L'\r'</code><dd>carriage return |
| |
| <br><dt><code>L'\t'</code><dd>horizontal tab |
| |
| <br><dt><code>L'\v'</code><dd>vertical tab |
| </dl> |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("space")) |
| </pre> |
| <p><a name="index-wctype_002eh-437"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-upper_002dcase-character-438"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswupper</b> (<var>wint_t wc</var>)<var><a name="index-iswupper-439"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is an upper-case letter. The letter need not be |
| from the Latin alphabet, any alphabet representable is valid. |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("upper")) |
| </pre> |
| <p><a name="index-wctype_002eh-440"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p><a name="index-hexadecimal-digit-character-441"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswxdigit</b> (<var>wint_t wc</var>)<var><a name="index-iswxdigit-442"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a hexadecimal digit. |
| Hexadecimal digits include the normal decimal digits ‘<samp><span class="samp">0</span></samp>’ through |
| ‘<samp><span class="samp">9</span></samp>’ and the letters ‘<samp><span class="samp">A</span></samp>’ through ‘<samp><span class="samp">F</span></samp>’ and |
| ‘<samp><span class="samp">a</span></samp>’ through ‘<samp><span class="samp">f</span></samp>’. |
| |
| <p class="noindent">This function can be implemented using |
| |
| <pre class="smallexample"> iswctype (wc, wctype ("xdigit")) |
| </pre> |
| <p><a name="index-wctype_002eh-443"></a>It is declared in <samp><span class="file">wctype.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p>The GNU C library also provides a function which is not defined in the |
| ISO C<!-- /@w --> standard but which is available as a version for single byte |
| characters as well. |
| |
| <p><a name="index-blank-character-444"></a><!-- wctype.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>iswblank</b> (<var>wint_t wc</var>)<var><a name="index-iswblank-445"></a></var><br> |
| <blockquote><p>Returns true if <var>wc</var> is a blank character; that is, a space or a tab. |
| This function was originally a GNU extension, but was added in ISO C99<!-- /@w -->. |
| It is declared in <samp><span class="file">wchar.h</span></samp>. |
| </p></blockquote></div> |
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