islower

 

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isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
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Defined in header <ctype.h>
int islower(int ch );

Checks if the given character is classified as a lowercase character according to the current C locale. In the default "C" locale, islower returns true only for the lowercase letters (abcdefghijklmnopqrstuvwxyz).

If islower returns true, it is guaranteed that iscntrl, isdigit, ispunct, and isspace return false for the same character in the same C locale.

The behavior is undefined if the value of ch is not representable as unsignedchar and is not equal to EOF.

Parameters

ch

-

character to classify

Return value

Non-zero value if the character is a lowercase letter, zero otherwise.

Example

Run this code

#include <ctype.h>#include <locale.h>#include <stdio.h>   int main(void){unsignedchar c ='\xe5';// letter å in ISO-8859-1printf("In the default C locale, \\xe5 is %slowercase\n", islower(c)?"":"not ");setlocale(LC_ALL, "en_GB.iso88591");printf("In ISO-8859-1 locale, \\xe5 is %slowercase\n", islower(c)?"":"not ");}

Possible output:

In the default C locale, \xe5 is not lowercase In ISO-8859-1 locale, \xe5 is lowercase

References

• C23 standard (ISO/IEC 9899:2024):

• 7.4.1.7 The islower function (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• 7.4.1.7 The islower function (p: 146)

• C11 standard (ISO/IEC 9899:2011):

• 7.4.1.7 The islower function (p: 202)

• C99 standard (ISO/IEC 9899:1999):

• 7.4.1.7 The islower function (p: 183)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.3.1.6 The islower function

See also

iswlower (C95)	checks if a wide character is an lowercase character (function)
C++ documentation for islower

ASCII values			characters	iscntrl iswcntrl	isprint iswprint	isspace iswspace	isblank iswblank	isgraph iswgraph	ispunct iswpunct	isalnum iswalnum	isalpha iswalpha	isupper iswupper	islower iswlower	isdigit iswdigit	isxdigit iswxdigit
decimal	hexadecimal	octal
0–8	\x0–\x8	\0–\10	control codes (NUL, etc.)	≠0	0	0	0	0	0	0	0	0	0	0	0
9	\x9	\11	tab (\t)	≠0	0	≠0	≠0	0	0	0	0	0	0	0	0
10–13	\xA–\xD	\12–\15	whitespaces (\n, \v, \f, \r)	≠0	0	≠0	0	0	0	0	0	0	0	0	0
14–31	\xE–\x1F	\16–\37	control codes	≠0	0	0	0	0	0	0	0	0	0	0	0
32	\x20	\40	space	0	≠0	≠0	≠0	0	0	0	0	0	0	0	0
33–47	\x21–\x2F	\41–\57	!"#$%&'()*+,-./	0	≠0	0	0	≠0	≠0	0	0	0	0	0	0
48–57	\x30–\x39	\60–\71	0123456789	0	≠0	0	0	≠0	0	≠0	0	0	0	≠0	≠0
58–64	\x3A–\x40	\72–\100	:;<=>?@	0	≠0	0	0	≠0	≠0	0	0	0	0	0	0
65–70	\x41–\x46	\101–\106	ABCDEF	0	≠0	0	0	≠0	0	≠0	≠0	≠0	0	0	≠0
71–90	\x47–\x5A	\107–\132	GHIJKLMNOP QRSTUVWXYZ	0	≠0	0	0	≠0	0	≠0	≠0	≠0	0	0	0
91–96	\x5B–\x60	\133–\140	[\]^_`	0	≠0	0	0	≠0	≠0	0	0	0	0	0	0
97–102	\x61–\x66	\141–\146	abcdef	0	≠0	0	0	≠0	0	≠0	≠0	0	≠0	0	≠0
103–122	\x67–\x7A	\147–\172	ghijklmnop qrstuvwxyz	0	≠0	0	0	≠0	0	≠0	≠0	0	≠0	0	0
123–126	\x7B–\x7E	\173–\176	{|}~	0	≠0	0	0	≠0	≠0	0	0	0	0	0	0
127	\x7F	\177	backspace character (DEL)	≠0	0	0	0	0	0	0	0	0	0	0	0