isalpha(3) — Linux manual page

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

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)

Linux man-pages (unreleased)     (date)                       isalpha(3)

Pages that refer to this page: getopt(3)iswalnum(3)iswalpha(3)iswblank(3)iswcntrl(3)iswdigit(3)iswgraph(3)iswlower(3)iswprint(3)iswpunct(3)iswspace(3)iswupper(3)iswxdigit(3)localeconv(3)setlocale(3)sscanf(3)strtod(3)strtol(3)strtoul(3)toascii(3)toupper(3)wctype(3)bpf-helpers(7)locale(7)lsof(8)