isdigit

ISALPHA(3)                 Linux Programmer's Manual                ISALPHA(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, is-
       print_l, ispunct_l, isspace_l, isupper_l, isxdigit_l - character  clas-
       sification 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(), is-
       graph_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:
                  _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 un-
       signed 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  lo-
       cale  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 lo-
       cale object locale instead of the current locale.

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

       isalpha()
              checks  for an alphabetic character; in the standard "C" locale,
              it is equivalent to (isupper(c) ||  islower(c)).   In  some  lo-
              cales, 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"  lo-
              cales,  these are: space, form-feed ('\f'), newline ('\n'), car-
              riage 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(),  is-
       graph_l(),  islower_l(),  isprint_l(),  ispunct_l(), isspace_l(), isup-
       per_l(), isxdigit_l(), and isascii_l() are available since glibc 2.3.

ATTRIBUTES
       For an  explanation  of  the  terms  used  in  this  section,  see  at-
       tributes(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(),  iscn-
       trl_l(),   isdigit_l(),   isgraph_l(),  islower_l(),  isprint_l(),  is-
       punct_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 un-
       signed char.

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

SEE ALSO
       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)

COLOPHON
       This  page  is  part of release 5.05 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
       https://www.kernel.org/doc/man-pages/.

GNU                               2017-09-15                        ISALPHA(3)