Linux.com

iscntrl.3

ISALPHA

Section: Linux Programmer's Manual (3)
Updated: 2009-03-15
Index Return to Main Contents
 

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 equivalent to (isupper(c) || islower(c)). In some locales, there may be additional 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'), horizontal 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 (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), setlocale(3), toascii(3), tolower(3), toupper(3), ascii(7), locale(7)  

COLOPHON

This page is part of release 3.21 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
CONFORMING TO
NOTES
SEE ALSO
COLOPHON

 

Comments

Subscribe to Comments Feed

Upcoming Linux Foundation Courses

  1. LFS220 Linux System Administration
    05 Jan » 08 Jan - Virtual
    Details
  2. LFD331 Developing Linux Device Drivers
    12 Jan » 16 Jan - Virtual
    Details
  3. LFS520 OpenStack Cloud Architecture and Deployment
    12 Jan » 15 Jan - Virtual
    Details

View All Upcoming Courses

Become an Individual Member
Check out the Friday Funnies

Sign Up For the Linux.com Newsletter


Who we are ?

The Linux Foundation is a non-profit consortium dedicated to the growth of Linux.

More About the foundation...

Frequent Questions

Join / Linux Training / Board