ISALPHA(3)                 Linux Programmer's Manual                ISALPHA(3)

       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

       #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)):

               || /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _SVID_SOURCE

           _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(), isup-
       per_l(), isxdigit_l():
           Since glibc 2.10:
                  _XOPEN_SOURCE >= 700
           Before glibc 2.10:

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

       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

       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.

              checks for an alphanumeric character; it is equivalent to (isal-
              pha(c) || isdigit(c)).

              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.

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

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

              checks for a control character.

              checks for a digit (0 through 9).

              checks for any printable character except space.

              checks for a lowercase character.

              checks for any printable character including space.

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

              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

              checks for an uppercase letter.

              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.

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

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

       For  an  explanation  of  the  terms  used   in   this   section,   see

       |Interface                        | Attribute     | Value   |
       |isalnum(), isalpha(), isascii(), | Thread safety | MT-Safe |
       |isblank(), iscntrl(), isdigit(), |               |         |
       |isgraph(), islower(), isprint(), |               |         |
       |ispunct(), isspace(), isupper(), |               |         |
       |isxdigit()                       |               |         |
       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(),  iscn-
       trl_l(),    isdigit_l(),    isgraph_l(),    islower_l(),   isprint_l(),
       ispunct_l(), isspace_l(), isupper_l(), and isxdigit_l().

       isascii_l() is a GNU extension.

       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 (A) as
       an uppercase letter in the default C locale.

       iswalnum(3), iswalpha(3), iswblank(3), iswcntrl(3),  iswdigit(3),  isw-
       graph(3),  iswlower(3),  iswprint(3),  iswpunct(3), iswspace(3), iswup-
       per(3),   iswxdigit(3),   newlocale(3),    setlocale(3),    toascii(3),
       tolower(3), toupper(3), uselocale(3), ascii(7), locale(7)

       This  page  is  part of release 4.15 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at

GNU                               2017-09-15                        ISALPHA(3)
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