isalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace,

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ isalnum(), isalpha(), isascii(), isblank(), iscntrl(), isdigit(),           │ Thread safety │ MT-Safe │
       │ isgraph(), islower(), isprint(), ispunct(), isspace(), isupper(),           │               │         │
       │ isxdigit()                                                                  │               │         │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

       The standards require that the argument c  for  these  functions  is  either  EOF  or  a  value  that  is
       representable  in  the type unsignedchar; otherwise, the behavior is undefined.  If the argument c is of
       type char, it must be cast to unsignedchar, as in the following example:

           char c;
           ...
           res = toupper((unsigned char) c);

       This is necessary because char may be the equivalent of signedchar, 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
       unsignedchar.

       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.

       These  functions  check  whether  c,  which  must have the value of an unsignedchar 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 unsignedchar 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
              0123456789abcdefABCDEF.

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.

       Standard C library (libc, -lc)

       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

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

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 6.9.1                              2024-06-15                                         isalpha(3)

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.

#include<ctype.h>intisalnum(intc);intisalpha(intc);intiscntrl(intc);intisdigit(intc);intisgraph(intc);intislower(intc);intisprint(intc);intispunct(intc);intisspace(intc);intisupper(intc);intisxdigit(intc);intisascii(intc);intisblank(intc);intisalnum_l(intc,locale_tlocale);intisalpha_l(intc,locale_tlocale);intisblank_l(intc,locale_tlocale);intiscntrl_l(intc,locale_tlocale);intisdigit_l(intc,locale_tlocale);intisgraph_l(intc,locale_tlocale);intislower_l(intc,locale_tlocale);intisprint_l(intc,locale_tlocale);intispunct_l(intc,locale_tlocale);intisspace_l(intc,locale_tlocale);intisupper_l(intc,locale_tlocale);intisxdigit_l(intc,locale_tlocale);intisascii_l(intc,locale_tlocale);

   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