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islower, iswlower, _islower_l, _iswlower_l

Determines if a particular character is in lower case.

int islower(
   int c 
int iswlower(
   wint_t c 
int islower_l(
   int c,
   _locale_t locale
int _iswlower_l(
   wint_t c,
   _locale_t locale


Integer to test.


Locale to use.

Each of these routines returns nonzero if c is a particular representation of a lowercase character. islower returns a nonzero value if c is a lowercase character (a – z). iswlower returns a nonzero value if c is a wide character that corresponds to a lowercase letter, or if c is one of an implementation-defined set of wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace is nonzero. Each of these routines returns 0 if c does not satisfy the test condition.

When used with a release CRT library, islower will display a CRT assert if passed a parameter that is not EOF or in the range of 0 through 0xFF. When used with a debug CRT library, islower will use the parameter as an index into an array, with undefined results if the parameter is not EOF or in the range of 0 through 0xFF.

The versions of these functions with the _l suffix are identical except that they use the locale passed in instead of the current locale for their locale-dependent behavior. For more information, see Locale.

Generic-Text Routine Mappings

TCHAR.H routine

_UNICODE & _MBCS not defined

_MBCS defined

_UNICODE defined






_islower _l




Required header




<ctype.h> or <wchar.h>




<ctype.h> or <wchar.h>

For additional compatibility information, see Compatibility in the Introduction.