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islower

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 unsigned char 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

#include <stdio.h>
#include <ctype.h>
#include <locale.h>
 
int main(void)
{
    unsigned char c = '\xe5'; // letter å in ISO-8859-1
    printf("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 " );
}

Output:

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

References

  • 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

(C95)
 checks if a wide character is an lowercase character
(function)
C++ documentation for islower
ASCII values
(hex) 		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.
0 - 8 0x00-0x08 control codes (NUL, etc.) ≠0 0 0 0 0 0 0 0 0 0 0 0
9 0x09 tab (\t) ≠0 0 ≠0 ≠0 0 0 0 0 0 0 0 0
10 - 13 0x0A-0x0D whitespaces (\n,\v,\f,\r) ≠0 0 ≠0 0 0 0 0 0 0 0 0 0
14 - 31 0x0E-0x1F control codes ≠0 0 0 0 0 0 0 0 0 0 0 0
32 0x20 space 0 ≠0 ≠0 ≠0 0 0 0 0 0 0 0 0
33 - 47 0x21-0x2F !"#$%&'()*+,-./ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
48 - 57 0x30-0x39 0123456789 0 ≠0 0 0 ≠0 0 ≠0 0 0 0 ≠0 ≠0
58 - 64 0x3a-0x40 :;<=>?@ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
65 - 70 0x41-0x46 ABCDEF 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 ≠0
71 - 90 0x47-0x5A GHIJKLMNOPQRSTUVWXYZ 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 0
91 - 96 0x5B-0x60 [\]^_` 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
97 -102 0x61-0x66 abcdef 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 ≠0
103-122 0x67-0x7A ghijklmnopqrstuvwxyz 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 0
123-126 0x7B-0x7E {|}~ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
127 0x7F backspace character (DEL) ≠0 0 0 0 0 0 0 0 0 0 0 0

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