ISLOWER(3) Library Functions Manual ISLOWER(3)

islower — test for a lowercase letter

#include <ctype.h>

int islower(int c);

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 IEEE Std 1003.1-2001 (“POSIX.1”) defers to the ISO C standard.

The islower () function shall test whether c is a character of class in the program's current locale; see the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), xbd_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 () function shall return non-zero if c is a lowercase letter; otherwise, it shall return 0.

No errors are defined.

The following example tests whether the value is a lowercase letter, based on the locale of the user, then uses it as part of a key value.

#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;
    }
...

To ensure applications portability, especially across natural languages, only this function and those listed in the SEE ALSO section should be used for character classification.

None.

None.

isalnum(3) , isalpha(3) , iscntrl(3) , isdigit(3) , isgraph(3) , isprint(3) , ispunct(3) , isspace(3) , isupper(3) , isxdigit(3) , setlocale(3) , the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), xbd_chap07(7), <ctype.h>

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

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

An example is added.

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December 6, 2001 posix.fail