1isalpha(3) Library Functions 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 Standard C library (libc, -lc)
14
16 #include <ctype.h>
17 int isalnum(int c);
19 int isalpha(int c);
20 int iscntrl(int c);
21 int isdigit(int c);
22 int isgraph(int c);
23 int islower(int c);
24 int isprint(int c);
25 int ispunct(int c);
26 int isspace(int c);
27 int isupper(int c);
28 int isxdigit(int c);
29 int isascii(int c);
31 int isblank(int c);
32 int isalnum_l(int c, locale_t locale);
34 int isalpha_l(int c, locale_t locale);
35 int isblank_l(int c, locale_t locale);
36 int iscntrl_l(int c, locale_t locale);
37 int isdigit_l(int c, locale_t locale);
38 int isgraph_l(int c, locale_t locale);
39 int islower_l(int c, locale_t locale);
40 int isprint_l(int c, locale_t locale);
41 int ispunct_l(int c, locale_t locale);
42 int isspace_l(int c, locale_t locale);
43 int isupper_l(int c, locale_t locale);
44 int isxdigit_l(int c, locale_t locale);
45 int isascii_l(int c, locale_t locale);
47 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
49 isascii():
51 _XOPEN_SOURCE
52 || /* glibc >= 2.19: */ _DEFAULT_SOURCE
53 || /* glibc <= 2.19: */ _SVID_SOURCE
54 isblank():
56 _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
57 salnum_l(), salpha_l(), sblank_l(), scntrl_l(), sdigit_l(), sgraph_l(),
59 slower_l(), sprint_l(), spunct_l(), sspace_l(), supper_l(),
60 sxdigit_l():
61 Since glibc 2.10:
62 _XOPEN_SOURCE >= 700
63 Before glibc 2.10:
64 _GNU_SOURCE
65 isascii_l():
67 Since glibc 2.10:
68 _XOPEN_SOURCE >= 700 && (_SVID_SOURCE || _BSD_SOURCE)
69 Before glibc 2.10:
70 _GNU_SOURCE
71
73 These functions check whether c, which must have the value of an un‐
74 signed char or EOF, falls into a certain character class according to
75 the specified locale. The functions without the "_l" suffix perform
76 the check based on the current locale.
77 The functions with the "_l" suffix perform the check based on the lo‐
79 cale specified by the locale object locale. The behavior of these
80 functions is undefined if locale is the special locale object
81 LC_GLOBAL_LOCALE (see duplocale(3)) or is not a valid locale object
82 handle.
83 The list below explains the operation of the functions without the "_l"
85 suffix; the functions with the "_l" suffix differ only in using the lo‐
86 cale object locale instead of the current locale.
87 isalnum()
89 checks for an alphanumeric character; it is equivalent to (isal‐
90 pha(c) || isdigit(c)).
91 isalpha()
93 checks for an alphabetic character; in the standard "C" locale,
94 it is equivalent to (isupper(c) || islower(c)). In some lo‐
95 cales, there may be additional characters for which isalpha() is
96 true—letters which are neither uppercase nor lowercase.
97 isascii()
99 checks whether c is a 7-bit unsigned char value that fits into
100 the ASCII character set.
101 isblank()
103 checks for a blank character; that is, a space or a tab.
104 iscntrl()
106 checks for a control character.
107 isdigit()
109 checks for a digit (0 through 9).
110 isgraph()
112 checks for any printable character except space.
113 islower()
115 checks for a lowercase character.
116 isprint()
118 checks for any printable character including space.
119 ispunct()
121 checks for any printable character which is not a space or an
122 alphanumeric character.
123 isspace()
125 checks for white-space characters. In the "C" and "POSIX" lo‐
126 cales, these are: space, form-feed ('\f'), newline ('\n'), car‐
127 riage return ('\r'), horizontal tab ('\t'), and vertical tab
128 ('\v').
129 isupper()
131 checks for an uppercase letter.
132 isxdigit()
134 checks for hexadecimal digits, that is, one of
135 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F.
136
138 The values returned are nonzero if the character c falls into the
139 tested class, and zero if not.
140
142 For an explanation of the terms used in this section, see at‐
143 tributes(7).
144 ┌────────────────────────────────────────────┬───────────────┬─────────┐
146 │Interface │ Attribute │ Value │
147 ├────────────────────────────────────────────┼───────────────┼─────────┤
148 │isalnum(), isalpha(), isascii(), isblank(), │ Thread safety │ MT-Safe │
149 │iscntrl(), isdigit(), isgraph(), islower(), │ │ │
150 │isprint(), ispunct(), isspace(), isupper(), │ │ │
151 │isxdigit() │ │ │
152 └────────────────────────────────────────────┴───────────────┴─────────┘
153
155 isalnum()
156 isalpha()
157 iscntrl()
158 isdigit()
159 isgraph()
160 islower()
161 isprint()
162 ispunct()
163 isspace()
164 isupper()
165 isxdigit()
166 isblank()
167 C11, POSIX.1-2008.
168 isascii()
170 isalnum_l()
171 isalpha_l()
172 isblank_l()
173 iscntrl_l()
174 isdigit_l()
175 isgraph_l()
176 islower_l()
177 isprint_l()
178 ispunct_l()
179 isspace_l()
180 isupper_l()
181 isxdigit_l()
182 POSIX.1-2008.
183 isascii_l()
185 GNU.
186
188 isalnum()
189 isalpha()
190 iscntrl()
191 isdigit()
192 isgraph()
193 islower()
194 isprint()
195 ispunct()
196 isspace()
197 isupper()
198 isxdigit()
199 C89, POSIX.1-2001.
200 isblank()
202 C99, POSIX.1-2001.
203 isascii()
205 POSIX.1-2001 (XSI).
206 POSIX.1-2008 marks it as obsolete, noting that it cannot be used
208 portably in a localized application.
209 isalnum_l()
211 isalpha_l()
212 isblank_l()
213 iscntrl_l()
214 isdigit_l()
215 isgraph_l()
216 islower_l()
217 isprint_l()
218 ispunct_l()
219 isspace_l()
220 isupper_l()
221 isxdigit_l()
222 glibc 2.3. POSIX.1-2008.
223 isascii_l()
225 glibc 2.3.
226
228 The standards require that the argument c for these functions is either
229 EOF or a value that is representable in the type unsigned char;
230 otherwise, the behavior is undefined. If the argument c is of type
231 char, it must be cast to unsigned char, as in the following example:
232 char c;
234 ...
235 res = toupper((unsigned char) c);
236 This is necessary because char may be the equivalent of signed char, in
238 which case a byte where the top bit is set would be sign extended when
239 converting to int, yielding a value that is outside the range of un‐
240 signed char.
241 The details of what characters belong to which class depend on the lo‐
243 cale. For example, isupper() will not recognize an A-umlaut (Ä) as an
244 uppercase letter in the default C locale.
245
247 iswalnum(3), iswalpha(3), iswblank(3), iswcntrl(3), iswdigit(3), isw‐
248 graph(3), iswlower(3), iswprint(3), iswpunct(3), iswspace(3), iswup‐
249 per(3), iswxdigit(3), newlocale(3), setlocale(3), toascii(3),
250 tolower(3), toupper(3), uselocale(3), ascii(7), locale(7)
251Linux man-pages 6.05 2023-07-30 isalpha(3)