Ascertains whether a given character is an uppercase letter

#include <ctype.h>
int isupper ( int c  );

The function isupper( ) tests whether its character argument is a capital letter. If the character is a uppercase letter, isupper( ) returns a nonzero value (that is, TRue); if not, the function returns 0 (false).

Which characters are letters and which letters are uppercase both depend on the current locale setting for the category LC_CTYPE, which you can query or change using the setlocale( ) function. In the default locale C, the truth values of isupper( ) and islower( ) are mutually exclusive for the alphabetic characters. However, other locales may have alphabetic characters for which both isupper( ) and islower( ) return true, or characters which are alphabetic, but are neither upper- nor lowercase.

Example

See the examples at setlocale( ) and isprint( ) in this chapter.

See Also

islower( ), tolower( ), toupper( ); the corresponding C99 function for wide characters, iswupper( ); isalnum( ), isalpha( ), isblank( ), iscntrl( ), isdigit( ), isgraph( ), isprint( ), ispunct( ), isspace( ), isxdigit( ), setlocale( )