Determines if a particular character is in upper case.
int isupper(
   int c 
);
int _isupper_l (
   int c,
   _locale_t locale
);
int iswupper(
   wint_t c 
);
int _iwsupper_l(
   wint_t c,
   _locale_t locale 
);
Parameters
- c 
 Integer to test.
- locale 
 Locale to use.
Return Value
Each of these routines returns nonzero if c is a particular representation of an uppercase letter. isupper returns a nonzero value if c is an uppercase character (A – Z). iswupper returns a nonzero value if c is a wide character that corresponds to an uppercase 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 debug CRT library, isupper 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, isupper 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 | 
|---|---|---|---|
| _istupper | isupper | iswupper | |
| _istupper_l | _isupper_l | _iswupper_l | 
Requirements
| Routine | Required header | 
|---|---|
| isupper | <ctype.h> | 
| _isupper_l | <ctype.h> | 
| iswupper | <ctype.h> or <wchar.h> | 
| _iswupper_l | <ctype.h> | 
For additional compatibility information, see Compatibility in the Introduction.