C in a Nutshell

Name

isupper

Synopsis

Ascertains whether a given character is an uppercase letter

#include <ctype.h>
intisupper( 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()