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man:islower

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,
     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(), 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
     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 (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
            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(), 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
     attributes(7).
     allbox; lbw32 lb lb l l l.  Interface Attribute Value T{ isalnum(),
     isalpha(), isascii(), isblank(), iscntrl(), isdigit(), isgraph(),
     islower(), isprint(), ispunct(), isspace(), isupper(), isxdigit()
     T}   Thread safety   MT-Safe

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(),
     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), 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 4.16 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)

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