'\" et
.TH ISLOWER "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
islower,
islower_l
\(em test for a lowercase letter
.SH SYNOPSIS
.LP
.nf
#include <ctype.h>
.P
int islower(int \fIc\fP);
int islower_l(int \fIc\fP, locale_t \fIlocale\fP);
.fi
.SH DESCRIPTION
For
\fIislower\fR():
The functionality described on this reference page is aligned with the
ISO\ C standard. Any conflict between the requirements described here and the
ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
.P
The
\fIislower\fR()
and
\fIislower_l\fR()
functions shall test whether
.IR c
is a character of class
.BR lower
in the current locale,
or in the locale represented by
.IR locale ,
respectively; see the Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 7" ", " "Locale".
.P
The
.IR c
argument is an
.BR int ,
the value of which the application shall ensure is a character
representable as an
.BR "unsigned char"
or equal to the value of the macro EOF. If the argument has any other
value, the behavior is undefined.
.P
The behavior is undefined if the
.IR locale
argument to
\fIislower_l\fR()
is the special locale object LC_GLOBAL_LOCALE or is not a valid locale
object handle.
.SH "RETURN VALUE"
The
\fIislower\fR()
and
\fIislower_l\fR()
functions shall return non-zero if
.IR c
is a lowercase letter; otherwise, they shall return 0.
.SH ERRORS
No errors are defined.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Testing for a Lowercase Letter"
.P
Two examples follow, the first using
\fIislower\fR(),
the second using multiple concurrent locales and
\fIislower_l\fR().
.P
The examples test whether the value is a lowercase letter,
based on the current locale, then use it as part of a key value.
.sp
.RS 4
.nf

/* Example 1 -- using islower() */
#include <ctype.h>
#include <stdlib.h>
#include <locale.h>
\&...
char *keystr;
int elementlen, len;
unsigned char c;
\&...
setlocale(LC_ALL, "");
\&...
len = 0;
while (len < elementlen) {
    c = (unsigned char) (rand() % 256);
\&...
    if (islower(c))
        keystr[len++] = c;
    }
\&...
.P
/* Example 2 -- using islower_l() */
#include <ctype.h>
#include <stdlib.h>
#include <locale.h>
\&...
char *keystr;
int elementlen, len;
unsigned char c;
\&...
locale_t loc = newlocale (LC_ALL_MASK, "", (locale_t) 0);
\&...
len = 0;
while (len < elementlen) {
    c = (unsigned char) (rand() % 256);
\&...
    if (islower_l(c, loc))
        keystr[len++] = c;
    }
\&...
.fi
.P
.RE
.SH "APPLICATION USAGE"
To ensure applications portability, especially across natural
languages, only these functions and the functions in the reference pages
listed in the SEE ALSO section should be used for character classification.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIisalnum\fR\^(\|)",
.IR "\fIisalpha\fR\^(\|)",
.IR "\fIisblank\fR\^(\|)",
.IR "\fIiscntrl\fR\^(\|)",
.IR "\fIisdigit\fR\^(\|)",
.IR "\fIisgraph\fR\^(\|)",
.IR "\fIisprint\fR\^(\|)",
.IR "\fIispunct\fR\^(\|)",
.IR "\fIisspace\fR\^(\|)",
.IR "\fIisupper\fR\^(\|)",
.IR "\fIisxdigit\fR\^(\|)",
.IR "\fIsetlocale\fR\^(\|)",
.IR "\fIuselocale\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 7" ", " "Locale",
.IR "\fB<ctype.h>\fP",
.IR "\fB<locale.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .