cpp/string/byte/isupper

Checks if the given character is an uppercase character as classified by the currently installed C locale. In the default locale,  returns a nonzero value only for the uppercase letters.

If returns a nonzero value, it is guaranteed that std, std, std, and std return zero for the same character in the same C locale.

The behavior is undefined if the value of is not representable as  and is not equal to.

Return value
Non-zero value if the character is an uppercase letter, zero otherwise.