islower

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

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 " );
}

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