1ISALPHA(3) Linux Programmer's Manual ISALPHA(3)
2
6 isalnum, isalpha, isascii, isblank, iscntrl, isdigit, isgraph, islower,
7 isprint, ispunct, isspace, isupper, isxdigit, isalnum_l, isalpha_l,
8 isascii_l, isblank_l, iscntrl_l, isdigit_l, isgraph_l, islower_l, is‐
9 print_l, ispunct_l, isspace_l, isupper_l, isxdigit_l - character clas‐
10 sification functions
11
13 #include <ctype.h>
14 int isalnum(int c);
16 int isalpha(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);
26 int isascii(int c);
28 int isblank(int c);
29 int isalnum_l(int c, locale_t locale);
31 int isalpha_l(int c, locale_t locale);
32 int isblank_l(int c, locale_t locale);
33 int iscntrl_l(int c, locale_t locale);
34 int isdigit_l(int c, locale_t locale);
35 int isgraph_l(int c, locale_t locale);
36 int islower_l(int c, locale_t locale);
37 int isprint_l(int c, locale_t locale);
38 int ispunct_l(int c, locale_t locale);
39 int isspace_l(int c, locale_t locale);
40 int isupper_l(int c, locale_t locale);
41 int isxdigit_l(int c, locale_t locale);
42 int isascii_l(int c, locale_t locale);
44 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
46 isascii():
48 _XOPEN_SOURCE
49 || /* Glibc since 2.19: */ _DEFAULT_SOURCE
50 || /* Glibc versions <= 2.19: */ _SVID_SOURCE
51 isblank():
53 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
54 isalnum_l(), isalpha_l(), isblank_l(), iscntrl_l(), isdigit_l(), is‐
56 graph_l(), islower_l(), isprint_l(), ispunct_l(), isspace_l(), isup‐
57 per_l(), isxdigit_l():
58 Since glibc 2.10:
59 _XOPEN_SOURCE >= 700
60 Before glibc 2.10:
61 _GNU_SOURCE
62 isascii_l():
64 Since glibc 2.10:
65 _XOPEN_SOURCE >= 700 && (_SVID_SOURCE || _BSD_SOURCE)
66 Before glibc 2.10:
67 _GNU_SOURCE
68
70 These functions check whether c, which must have the value of an un‐
71 signed char or EOF, falls into a certain character class according to
72 the specified locale. The functions without the "_l" suffix perform
73 the check based on the current locale.
74 The functions with the "_l" suffix perform the check based on the lo‐
76 cale specified by the locale object locale. The behavior of these
77 functions is undefined if locale is the special locale object
78 LC_GLOBAL_LOCALE (see duplocale(3)) or is not a valid locale object
79 handle.
80 The list below explains the operation of the functions without the "_l"
82 suffix; the functions with the "_l" suffix differ only in using the lo‐
83 cale object locale instead of the current locale.
84 isalnum()
86 checks for an alphanumeric character; it is equivalent to (isal‐
87 pha(c) || isdigit(c)).
88 isalpha()
90 checks for an alphabetic character; in the standard "C" locale,
91 it is equivalent to (isupper(c) || islower(c)). In some lo‐
92 cales, there may be additional characters for which isalpha() is
93 true—letters which are neither uppercase nor lowercase.
94 isascii()
96 checks whether c is a 7-bit unsigned char value that fits into
97 the ASCII character set.
98 isblank()
100 checks for a blank character; that is, a space or a tab.
101 iscntrl()
103 checks for a control character.
104 isdigit()
106 checks for a digit (0 through 9).
107 isgraph()
109 checks for any printable character except space.
110 islower()
112 checks for a lowercase character.
113 isprint()
115 checks for any printable character including space.
116 ispunct()
118 checks for any printable character which is not a space or an
119 alphanumeric character.
120 isspace()
122 checks for white-space characters. In the "C" and "POSIX" lo‐
123 cales, these are: space, form-feed ('\f'), newline ('\n'), car‐
124 riage return ('\r'), horizontal tab ('\t'), and vertical tab
125 ('\v').
126 isupper()
128 checks for an uppercase letter.
129 isxdigit()
131 checks for hexadecimal digits, that is, one of
132 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.
133
135 The values returned are nonzero if the character c falls into the
136 tested class, and zero if not.
137
139 isalnum_l(), isalpha_l(), isblank_l(), iscntrl_l(), isdigit_l(), is‐
140 graph_l(), islower_l(), isprint_l(), ispunct_l(), isspace_l(), isup‐
141 per_l(), isxdigit_l(), and isascii_l() are available since glibc 2.3.
142
144 For an explanation of the terms used in this section, see at‐
145 tributes(7).
146 ┌─────────────────────────────────┬───────────────┬─────────┐
148 │Interface │ Attribute │ Value │
149 ├─────────────────────────────────┼───────────────┼─────────┤
150 │isalnum(), isalpha(), isascii(), │ Thread safety │ MT-Safe │
151 │isblank(), iscntrl(), isdigit(), │ │ │
152 │isgraph(), islower(), isprint(), │ │ │
153 │ispunct(), isspace(), isupper(), │ │ │
154 │isxdigit() │ │ │
155 └─────────────────────────────────┴───────────────┴─────────┘
157 C89 specifies isalnum(), isalpha(), iscntrl(), isdigit(), isgraph(),
158 islower(), isprint(), ispunct(), isspace(), isupper(), and isxdigit(),
159 but not isascii() and isblank(). POSIX.1-2001 also specifies those
160 functions, and also isascii() (as an XSI extension) and isblank(). C99
161 specifies all of the preceding functions, except isascii().
162 POSIX.1-2008 marks isascii() as obsolete, noting that it cannot be used
164 portably in a localized application.
165 POSIX.1-2008 specifies isalnum_l(), isalpha_l(), isblank_l(), iscn‐
167 trl_l(), isdigit_l(), isgraph_l(), islower_l(), isprint_l(), is‐
168 punct_l(), isspace_l(), isupper_l(), and isxdigit_l().
169 isascii_l() is a GNU extension.
171
173 The standards require that the argument c for these functions is either
174 EOF or a value that is representable in the type unsigned char. If the
175 argument c is of type char, it must be cast to unsigned char, as in the
176 following example:
177 char c;
179 ...
180 res = toupper((unsigned char) c);
181 This is necessary because char may be the equivalent of signed char, in
183 which case a byte where the top bit is set would be sign extended when
184 converting to int, yielding a value that is outside the range of un‐
185 signed char.
186 The details of what characters belong to which class depend on the lo‐
188 cale. For example, isupper() will not recognize an A-umlaut (Ä) as an
189 uppercase letter in the default C locale.
190
192 iswalnum(3), iswalpha(3), iswblank(3), iswcntrl(3), iswdigit(3), isw‐
193 graph(3), iswlower(3), iswprint(3), iswpunct(3), iswspace(3), iswup‐
194 per(3), iswxdigit(3), newlocale(3), setlocale(3), toascii(3),
195 tolower(3), toupper(3), uselocale(3), ascii(7), locale(7)
196
198 This page is part of release 5.10 of the Linux man-pages project. A
199 description of the project, information about reporting bugs, and the
200 latest version of this page, can be found at
201 https://www.kernel.org/doc/man-pages/.
202GNU 2017-09-15 ISALPHA(3)