isalpha(3) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | CAVEATS | SEE ALSO | COLOPHON

isalpha(3)              Library Functions Manual              isalpha(3)

NAME         top

       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

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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 >= 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _SVID_SOURCE

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

       salnum_l(), salpha_l(), sblank_l(), scntrl_l(), sdigit_l(),
       sgraph_l(), slower_l(), sprint_l(), spunct_l(), sspace_l(),
       supper_l(), sxdigit_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         top

       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         top

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

ATTRIBUTES         top

       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()                          │               │         │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS         top

       isalnum()
       isalpha()
       iscntrl()
       isdigit()
       isgraph()
       islower()
       isprint()
       ispunct()
       isspace()
       isupper()
       isxdigit()
       isblank()
              C11, POSIX.1-2008.

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

       isascii_l()
              GNU.

HISTORY         top

       isalnum()
       isalpha()
       iscntrl()
       isdigit()
       isgraph()
       islower()
       isprint()
       ispunct()
       isspace()
       isupper()
       isxdigit()
              C89, POSIX.1-2001.

       isblank()
              C99, POSIX.1-2001.

       isascii()
              POSIX.1-2001 (XSI).

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

       isalnum_l()
       isalpha_l()
       isblank_l()
       iscntrl_l()
       isdigit_l()
       isgraph_l()
       islower_l()
       isprint_l()
       ispunct_l()
       isspace_l()
       isupper_l()
       isxdigit_l()
              glibc 2.3.  POSIX.1-2008.

       isascii_l()
              glibc 2.3.

CAVEATS         top

       The standards require that the argument c for these functions is
       either EOF or a value that is representable in the type unsigned
       char; otherwise, the behavior is undefined.  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         top

       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         top

       This page is part of the man-pages (Linux kernel and C library
       user-space interface documentation) project.  Information about
       the project can be found at 
       ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report
       for this manual page, see
       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
       This page was obtained from the tarball man-pages-6.9.1.tar.gz
       fetched from
       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
       2024-06-26.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to
       man-pages@man7.org

Linux man-pages 6.9.1          2024-06-15                     isalpha(3)

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