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(),
       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 (Ä) 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
       This page is part of release 5.02 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)