1ISLOWER(3P) POSIX Programmer's Manual ISLOWER(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 islower, islower_l — test for a lowercase letter
13
15 #include <ctype.h>
16 int islower(int c);
18 int islower_l(int c, locale_t locale);
19
21 For islower(): The functionality described on this reference page is
22 aligned with the ISO C standard. Any conflict between the requirements
23 described here and the ISO C standard is unintentional. This volume of
24 POSIX.1‐2017 defers to the ISO C standard.
25 The islower() and islower_l() functions shall test whether c is a char‐
27 acter of class lower in the current locale, or in the locale repre‐
28 sented by locale, respectively; see the Base Definitions volume of
29 POSIX.1‐2017, Chapter 7, Locale.
30 The c argument is an int, the value of which the application shall
32 ensure is a character representable as an unsigned char or equal to the
33 value of the macro EOF. If the argument has any other value, the behav‐
34 ior is undefined.
35 The behavior is undefined if the locale argument to islower_l() is the
37 special locale object LC_GLOBAL_LOCALE or is not a valid locale object
38 handle.
39
41 The islower() and islower_l() functions shall return non-zero if c is a
42 lowercase letter; otherwise, they shall return 0.
43
45 No errors are defined.
46 The following sections are informative.
48
50 Testing for a Lowercase Letter
51 Two examples follow, the first using islower(), the second using multi‐
52 ple concurrent locales and islower_l().
53 The examples test whether the value is a lowercase letter, based on the
55 current locale, then use it as part of a key value.
56 /* Example 1 -- using islower() */
59 #include <ctype.h>
60 #include <stdlib.h>
61 #include <locale.h>
62 ...
63 char *keystr;
64 int elementlen, len;
65 unsigned char c;
66 ...
67 setlocale(LC_ALL, "");
68 ...
69 len = 0;
70 while (len < elementlen) {
71 c = (unsigned char) (rand() % 256);
72 ...
73 if (islower(c))
74 keystr[len++] = c;
75 }
76 ...
77 /* Example 2 -- using islower_l() */
79 #include <ctype.h>
80 #include <stdlib.h>
81 #include <locale.h>
82 ...
83 char *keystr;
84 int elementlen, len;
85 unsigned char c;
86 ...
87 locale_t loc = newlocale (LC_ALL_MASK, "", (locale_t) 0);
88 ...
89 len = 0;
90 while (len < elementlen) {
91 c = (unsigned char) (rand() % 256);
92 ...
93 if (islower_l(c, loc))
94 keystr[len++] = c;
95 }
96 ...
97
99 To ensure applications portability, especially across natural lan‐
100 guages, only these functions and the functions in the reference pages
101 listed in the SEE ALSO section should be used for character classifica‐
102 tion.
103
105 None.
106
108 None.
109
111 isalnum(), isalpha(), isblank(), iscntrl(), isdigit(), isgraph(),
112 isprint(), ispunct(), isspace(), isupper(), isxdigit(), setlocale(),
113 uselocale()
114 The Base Definitions volume of POSIX.1‐2017, Chapter 7, Locale,
116 <ctype.h>, <locale.h>
117
119 Portions of this text are reprinted and reproduced in electronic form
120 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
121 table Operating System Interface (POSIX), The Open Group Base Specifi‐
122 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
123 Electrical and Electronics Engineers, Inc and The Open Group. In the
124 event of any discrepancy between this version and the original IEEE and
125 The Open Group Standard, the original IEEE and The Open Group Standard
126 is the referee document. The original Standard can be obtained online
127 at http://www.opengroup.org/unix/online.html .
128 Any typographical or formatting errors that appear in this page are
130 most likely to have been introduced during the conversion of the source
131 files to man page format. To report such errors, see https://www.ker‐
132 nel.org/doc/man-pages/reporting_bugs.html .
133IEEE/The Open Group 2017 ISLOWER(3P)