(libc.info.gz) Classification of Wide Characters

Info Catalog (libc.info.gz) Case Conversion (libc.info.gz) Character Handling (libc.info.gz) Using Wide Char Classes
 
 4.3 Character class determination for wide characters
 =====================================================
 
 Amendment 1 to ISO C90 defines functions to classify wide characters.
 Although the original ISO C90 standard already defined the type
 'wchar_t', no functions operating on them were defined.
 
    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 'localedef'
 program.
 
    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.
 
    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 'char'
 objects can be defined.
 
  -- Data type: wctype_t
      The 'wctype_t' can hold a value which represents a character class.
      The only defined way to generate such a value is by using the
      'wctype' function.
 
      This type is defined in 'wctype.h'.
 
  -- Function: wctype_t wctype (const char *PROPERTY)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      The 'wctype' returns a value representing a class of wide
      characters which is identified by the string PROPERTY.  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 'LC_CTYPE' category, the function returns zero.
 
      The properties known in every locale are:
 
      '"alnum"'          '"alpha"'          '"cntrl"'          '"digit"'
      '"graph"'          '"lower"'          '"print"'          '"punct"'
      '"space"'          '"upper"'          '"xdigit"'
 
      This function is declared in 'wctype.h'.
 
    To test the membership of a character to one of the non-standard
 classes the ISO C standard defines a completely new function.
 
  -- Function: int iswctype (wint_t WC, wctype_t DESC)
      Preliminary: | MT-Safe | AS-Safe | AC-Safe |  POSIX Safety
      Concepts.
 
      This function returns a nonzero value if WC is in the character
      class specified by DESC.  DESC must previously be returned by a
      successful call to 'wctype'.
 
      This function is declared in 'wctype.h'.
 
    To make it easier to use the commonly-used classification functions,
 they are defined in the C library.  There is no need to use 'wctype' 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 'wctype' can also handle the standard classes.
 
  -- Function: int iswalnum (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      This function returns a nonzero value if WC is an alphanumeric
      character (a letter or number); in other words, if either
      'iswalpha' or 'iswdigit' is true of a character, then 'iswalnum' is
      also true.
 
      This function can be implemented using
 
           iswctype (wc, wctype ("alnum"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswalpha (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is an alphabetic character (a letter).  If
      'iswlower' or 'iswupper' is true of a character, then 'iswalpha' is
      also true.
 
      In some locales, there may be additional characters for which
      'iswalpha' is true--letters which are neither upper case nor lower
      case.  But in the standard '"C"' locale, there are no such
      additional characters.
 
      This function can be implemented using
 
           iswctype (wc, wctype ("alpha"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswcntrl (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a control character (that is, a character
      that is not a printing character).
 
      This function can be implemented using
 
           iswctype (wc, wctype ("cntrl"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswdigit (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a digit (e.g., '0' through '9').  Please note
      that this function does not only return a nonzero value for
      _decimal_ digits, but for all kinds of digits.  A consequence is
      that code like the following will *not* work unconditionally for
      wide characters:
 
           n = 0;
           while (iswdigit (*wc))
             {
               n *= 10;
               n += *wc++ - L'0';
             }
 
      This function can be implemented using
 
           iswctype (wc, wctype ("digit"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswgraph (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a graphic character; that is, a character
      that has a glyph associated with it.  The whitespace characters are
      not considered graphic.
 
      This function can be implemented using
 
           iswctype (wc, wctype ("graph"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswlower (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a lower-case letter.  The letter need not be
      from the Latin alphabet, any alphabet representable is valid.
 
      This function can be implemented using
 
           iswctype (wc, wctype ("lower"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswprint (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a printing character.  Printing characters
      include all the graphic characters, plus the space (' ') character.
 
      This function can be implemented using
 
           iswctype (wc, wctype ("print"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswpunct (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a punctuation character.  This means any
      printing character that is not alphanumeric or a space character.
 
      This function can be implemented using
 
           iswctype (wc, wctype ("punct"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswspace (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a "whitespace" character.  In the standard
      '"C"' locale, 'iswspace' returns true for only the standard
      whitespace characters:
 
      'L' ''
           space
 
      'L'\f''
           formfeed
 
      'L'\n''
           newline
 
      'L'\r''
           carriage return
 
      'L'\t''
           horizontal tab
 
      'L'\v''
           vertical tab
 
      This function can be implemented using
 
           iswctype (wc, wctype ("space"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswupper (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is an upper-case letter.  The letter need not be
      from the Latin alphabet, any alphabet representable is valid.
 
      This function can be implemented using
 
           iswctype (wc, wctype ("upper"))
 
      It is declared in 'wctype.h'.
 
  -- Function: int iswxdigit (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a hexadecimal digit.  Hexadecimal digits
      include the normal decimal digits '0' through '9' and the letters
      'A' through 'F' and 'a' through 'f'.
 
      This function can be implemented using
 
           iswctype (wc, wctype ("xdigit"))
 
      It is declared in 'wctype.h'.
 
    The GNU C Library also provides a function which is not defined in
 the ISO C standard but which is available as a version for single byte
 characters as well.
 
  -- Function: int iswblank (wint_t WC)
      Preliminary: | MT-Safe locale | AS-Safe | AC-Safe |  POSIX
      Safety Concepts.
 
      Returns true if WC is a blank character; that is, a space or a tab.
      This function was originally a GNU extension, but was added in
      ISO C99.  It is declared in 'wchar.h'.
 
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