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ISALPHA(3)                 Linux Programmer's Manual                ISALPHA(3)



NAME
       isalnum,  isalpha,  isascii,  isblank, iscntrl, isdigit, isgraph, islower, isprint,
       ispunct, isspace, isupper, isxdigit - character classification routines

SYNOPSIS
       #include <ctype.h>

       int isalnum(int c);
       int isalpha(int c);
       int isascii(int c);
       int isblank(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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       isascii(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
       isblank(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99

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 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 equiv-
              alent  to  (isupper(c)  || islower(c)).  In some locales, there may be addi-
              tional characters for which isalpha()  is  true--letters  which  are  neither
              upper case nor lower case.

       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 lower-case 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'),  hori-
              zontal tab ('\t'), and vertical tab ('\v').

       isupper()
              checks for an uppercase letter.

       isxdigit()
              checks for a 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 non-zero if the character c falls into the tested class,
       and a zero value if not.

CONFORMING TO
       C99, 4.3BSD.  C89 specifies all of these functions except isascii() and  isblank().
       isascii()  is a BSD extension and is also an SVr4 extension.  isblank() conforms to
       POSIX.1-2001 and C99 7.4.1.3.  POSIX.1-2008 marks  isascii()  as  obsolete,  noting
       that it cannot be used portably in a localized application.

NOTES
       The  details  of  what  characters  belong  into  which class depend on the current
       locale.  For example, isupper() will not recognize an A-umlaut (A) 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), set-
       locale(3), toascii(3), tolower(3), toupper(3), ascii(7), locale(7)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



GNU                               2009-03-15                        ISALPHA(3)

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