isalnum(3)

NAME

   isalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower,
   isprint, ispunct, isspace,  isupper,  isxdigit,  isalnum_l,  isalpha_l,
   isascii_l,   isblank_l,  iscntrl_l,  isdigit_l,  isgraph_l,  islower_l,
   isprint_l, ispunct_l,  isspace_l,  isupper_l,  isxdigit_l  -  character
   classification functions

SYNOPSIS

   #include <ctype.h>

   int isalnum(int c);
   int isalpha(int c);
   int iscntrl(int c);
   int isdigit(int c);
   int isgraph(int c);
   int islower(int c);
   int isprint(int c);
   int ispunct(int c);
   int isspace(int c);
   int isupper(int c);
   int isxdigit(int c);

   int isascii(int c);
   int isblank(int c);

   int isalnum_l(int c, locale_t locale);
   int isalpha_l(int c, locale_t locale);
   int isblank_l(int c, locale_t locale);
   int iscntrl_l(int c, locale_t locale);
   int isdigit_l(int c, locale_t locale);
   int isgraph_l(int c, locale_t locale);
   int islower_l(int c, locale_t locale);
   int isprint_l(int c, locale_t locale);
   int ispunct_l(int c, locale_t locale);
   int isspace_l(int c, locale_t locale);
   int isupper_l(int c, locale_t locale);
   int isxdigit_l(int c, locale_t locale);

   int isascii_l(int c, locale_t locale);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   isascii():
       _XOPEN_SOURCE
           || /* Glibc since 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _SVID_SOURCE

   isblank():
       _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

   isalnum_l(), isalpha_l(), isblank_l(), iscntrl_l(), isdigit_l(),
   isgraph_l(), islower_l(), isprint_l(), ispunct_l(), isspace_l(),
   isupper_l(), isxdigit_l():
       Since glibc 2.10:
              _XOPEN_SOURCE >= 700
       Before glibc 2.10:
              _GNU_SOURCE

   isascii_l():
       Since glibc 2.10:
              _XOPEN_SOURCE >= 700 && (_SVID_SOURCE || _BSD_SOURCE)
       Before glibc 2.10:
              _GNU_SOURCE

DESCRIPTION

   These  functions  check  whether  c,  which  must  have the value of an
   unsigned char or EOF, falls into a certain character class according to
   the  specified  locale.   The functions without the "_l" suffix perform
   the check based on the current locale.

   The functions with the "_l" suffix  perform  the  check  based  on  the
   locale  specified  by  the locale object locale.  The behavior of these
   functions  is  undefined  if  locale  is  the  special  locale   object
   LC_GLOBAL_LOCALE  (see  duplocale(3))  or  is not a valid locale object
   handle.

   The list below explains the operation of the functions without the "_l"
   suffix;  the  functions  with  the "_l" suffix differ only in using the
   locale object locale instead of the current locale.

   isalnum()
          checks for  an  alphanumeric  character;  it  is  equivalent  to
          (isalpha(c) || isdigit(c)).

   isalpha()
          checks  for an alphabetic character; in the standard "C" locale,
          it  is  equivalent  to  (isupper(c)  ||  islower(c)).   In  some
          locales,  there may be additional characters for which isalpha()
          is true---letters which are neither uppercase nor lowercase.

   isascii()
          checks whether c is a 7-bit unsigned char value that  fits  into
          the ASCII character set.

   isblank()
          checks for a blank character; that is, a space or a tab.

   iscntrl()
          checks for a control character.

   isdigit()
          checks for a digit (0 through 9).

   isgraph()
          checks for any printable character except space.

   islower()
          checks for a lowercase character.

   isprint()
          checks for any printable character including space.

   ispunct()
          checks  for  any  printable character which is not a space or an
          alphanumeric character.

   isspace()
          checks for white-space  characters.   In  the  "C"  and  "POSIX"
          locales,  these  are:  space,  form-feed ('\f'), newline ('\n'),
          carriage return ('\r'), horizontal tab ('\t'), and vertical  tab
          ('\v').

   isupper()
          checks for an uppercase letter.

   isxdigit()
          checks for hexadecimal digits, that is, one of
          0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.

RETURN VALUE

   The  values  returned  are  nonzero  if  the character c falls into the
   tested class, and zero if not.

VERSIONS

   isalnum_l(),  isalpha_l(),   isblank_l(),   iscntrl_l(),   isdigit_l(),
   isgraph_l(),   islower_l(),   isprint_l(),   ispunct_l(),  isspace_l(),
   isupper_l(), isxdigit_l(), and isascii_l() are  available  since  glibc
   2.3.

ATTRIBUTES

   For   an   explanation   of   the  terms  used  in  this  section,  see
   attributes(7).

   
   Interface                         Attribute      Value   
   
   isalnum(), isalpha(), isascii(),  Thread safety  MT-Safe 
   isblank(), iscntrl(), isdigit(),                         
   isgraph(), islower(), isprint(),                         
   ispunct(), isspace(), isupper(),                         
   isxdigit()                                               
   

CONFORMING TO

   C89 specifies isalnum(), isalpha(),  iscntrl(),  isdigit(),  isgraph(),
   islower(),  isprint(), ispunct(), isspace(), isupper(), and isxdigit(),
   but not isascii() and isblank().   POSIX.1-2001  also  specifies  those
   functions, and also isascii() (as an XSI extension) and isblank().  C99
   specifies all of the preceding functions, except isascii().

   POSIX.1-2008 marks isascii() as obsolete, noting that it cannot be used
   portably in a localized application.

   POSIX.1-2008    specifies    isalnum_l(),   isalpha_l(),   isblank_l(),
   iscntrl_l(),  isdigit_l(),   isgraph_l(),   islower_l(),   isprint_l(),
   ispunct_l(), isspace_l(), isupper_l(), and isxdigit_l().

   isascii_l() is a GNU extension.

NOTES

   The standards require that the argument c for these functions is either
   EOF or a value that is representable in the type unsigned char.  If the
   argument c is of type char, it must be cast to unsigned char, as in the
   following example:

       char c;
       ...
       res = toupper((unsigned char) c);

   This is necessary because char may be the equivalent of signed char, in
   which  case a byte where the top bit is set would be sign extended when
   converting to int, yielding a  value  that  is  outside  the  range  of
   unsigned char.

   The  details  of  what  characters  belong to which class depend on the
   locale.  For example, isupper() will not recognize an A-umlaut  ()  as
   an uppercase letter in the default C locale.

SEE ALSO

   iswalnum(3),   iswalpha(3),   iswblank(3),   iswcntrl(3),  iswdigit(3),
   iswgraph(3),  iswlower(3),   iswprint(3),   iswpunct(3),   iswspace(3),
   iswupper(3),   iswxdigit(3),  newlocale(3),  setlocale(3),  toascii(3),
   tolower(3), toupper(3), uselocale(3), ascii(7), locale(7)

COLOPHON

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   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at
   https://www.kernel.org/doc/man-pages/.

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