ISLOWER(3) Library Functions Manual ISLOWER(3)

islower islower_l — test for a lowercase letter

#include <ctype.h>

int islower(int c);
[CX] int islower_l(int c, locale_t locale);

For islower (): [CX] 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.1-2008 defers to the ISO C standard.

The islower () [CX] and islower_l () functions shall test whether c is a character of class in the current locale of the process, [CX] or in the locale represented by , respectively; see XBD V1_chap07(7) .

The c argument is an , the value of which the application shall ensure is a character representable as an or equal to the value of the macro EOF. If the argument has any other value, the behavior is undefined.

The islower () [CX] and islower_l () functions shall return non-zero if c is a lowercase letter; otherwise, they shall return 0.

The islower_l () function may fail if:

[CX] locale is not a valid locale object handle.

Two examples follow, the first using islower (), the second using multiple concurrent locales and islower_l ().

The examples test whether the value is a lowercase letter, based on the locale of the user, then use it as part of a key value.

/* Example 1 -- using islower() */
#include <ctype.h>
#include <stdlib.h>
#include <locale.h>
...
char *keystr;
int elementlen, len;
char c;
...
setlocale(LC_ALL, "");
...
len = 0;
while (len < elementlen) {
    c = (char) (rand() % 256);
...
    if (islower(c))
        keystr[len++] = c;
    }
...


/* Example 2 -- using islower_l() */
#include <ctype.h>
#include <stdlib.h>
#include <locale.h>
...
char *keystr;
int elementlen, len;
char c;
...
locale_t loc = newlocale (LC_ALL_MASK, "", (locale_t) 0);
...
len = 0;
while (len < elementlen) {
    c = (char) (rand() % 256);
...
    if (islower_l(c, loc))
        keystr[len++] = c;
    }
...

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.

None.

None.

isalnum(3) , isalpha(3) , isblank(3) , iscntrl(3) , isdigit(3) , isgraph(3) , isprint(3) , ispunct(3) , isspace(3) , isupper(3) , isxdigit(3) , setlocale(3) , uselocale(3)

XBD V1_chap07(7) , <ctype.h> , <locale.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The normative text is updated to avoid use of the term "must" for application requirements.

An example is added.

The islower_l () function is added from The Open Group Technical Standard, 2006, Extended API Set Part 4.

January 1, 2008 posix.fail