isdigit(3)

1ISALPHA(3)                 Linux Programmer's Manual                ISALPHA(3)
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NAME

6       isalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower,
7       isprint, ispunct, isspace, isupper, isxdigit - character classification
8       routines
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SYNOPSIS

11       #include <ctype.h>
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13       int isalnum(int c);
14       int isalpha(int c);
15       int isascii(int c);
16       int isblank(int c);
17       int iscntrl(int c);
18       int isdigit(int c);
19       int isgraph(int c);
20       int islower(int c);
21       int isprint(int c);
22       int ispunct(int c);
23       int isspace(int c);
24       int isupper(int c);
25       int isxdigit(int c);
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27   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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29       isascii(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE
30       isblank(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99
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DESCRIPTION

33       These  functions  check  whether  c,  which  must  have the value of an
34       unsigned char or EOF, falls into a certain character class according to
35       the current locale.
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37       isalnum()
38              checks for an alphanumeric character; it is equivalent to (isal‐
39              pha(c) || isdigit(c)).
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41       isalpha()
42              checks for an alphabetic character; in the standard "C"  locale,
43              it  is  equivalent  to  (isupper(c)  ||  islower(c)).   In  some
44              locales, there may be additional characters for which  isalpha()
45              is true—letters which are neither upper case nor lower case.
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47       isascii()
48              checks  whether  c is a 7-bit unsigned char value that fits into
49              the ASCII character set.
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51       isblank()
52              checks for a blank character; that is, a space or a tab.
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54       iscntrl()
55              checks for a control character.
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57       isdigit()
58              checks for a digit (0 through 9).
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60       isgraph()
61              checks for any printable character except space.
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63       islower()
64              checks for a lower-case character.
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66       isprint()
67              checks for any printable character including space.
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69       ispunct()
70              checks for any printable character which is not a  space  or  an
71              alphanumeric character.
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73       isspace()
74              checks  for  white-space  characters.   In  the  "C" and "POSIX"
75              locales, these are: space,  form-feed  ('\f'),  newline  ('\n'),
76              carriage  return ('\r'), horizontal tab ('\t'), and vertical tab
77              ('\v').
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79       isupper()
80              checks for an uppercase letter.
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82       isxdigit()
83              checks for a hexadecimal digits, that is, one of
84              0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.
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RETURN VALUE

87       The values returned are nonzero if  the  character  c  falls  into  the
88       tested class, and a zero value if not.
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CONFORMING TO

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

98       The  details  of  what characters belong into which class depend on the
99       current locale.  For example, isupper() will not recognize an  A-umlaut
100       (Ä) as an uppercase letter in the default C locale.
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COLOPHON

109       This page is part of release 3.25 of the Linux  man-pages  project.   A
110       description  of  the project, and information about reporting bugs, can
111       be found at http://www.kernel.org/doc/man-pages/.
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115GNU                               2009-03-15                        ISALPHA(3)