std::isupper(3)

NAME
std::isupper - std::isupper

Synopsis
   Defined in header <cctype>
   int isupper( int ch );
   Checks if the given character is an uppercase character as classified by the
   currently installed C locale. In the default "C" locale, std::isupper returns a
   nonzero value only for the uppercase letters (ABCDEFGHIJKLMNOPQRSTUVWXYZ).
   If std::isupper returns a nonzero value, it is guaranteed that std::iscntrl,
   std::isdigit, std::ispunct, and std::isspace return zero for the same character in
   the same C locale.
   The behavior is undefined if the value of ch is not representable as unsigned char
   and is not equal to EOF.

Parameters
   ch - character to classify

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

Notes
   Like all other functions from <cctype>, the behavior of std::isupper is undefined if
   the argument's value is neither representable as unsigned char nor equal to EOF. To
   use these functions safely with plain chars (or signed chars), the argument should
   first be converted to unsigned char:
 bool my_isupper(char ch)
 {
     return std::isupper(static_cast<unsigned char>(ch));
 }
   Similarly, they should not be directly used with standard algorithms when the
   iterator's value type is char or signed char. Instead, convert the value to unsigned
   char first:
 int count_uppers(const std::string& s)
 {
     return std::count_if(s.begin(), s.end(),
                       // static_cast<int(*)(int)>(std::isupper) // wrong
                       // [](int c){ return std::isupper(c); } // wrong
                       // [](char c){ return std::isupper(c); } // wrong
                        [](unsigned char c){ return std::isupper(c); } // correct
                        );
 }

Example
// Run this code
 #include <cctype>
 #include <clocale>
 #include <iostream>
 int main()
 {
     unsigned char c = '\xc6'; // letter Æ in ISO-8859-1
     std::cout << "isupper(\'\\xc6\', default C locale) returned "
               << std::boolalpha << (bool)std::isupper(c) << '\n';
     std::setlocale(LC_ALL, "en_GB.iso88591");
     std::cout << "isupper(\'\\xc6\', ISO-8859-1 locale) returned "
               << std::boolalpha << (bool)std::isupper(c) << '\n';
 }

Possible output:
 isupper('\xc6', default C locale) returned false
 isupper('\xc6', ISO-8859-1 locale) returned true

See also
   isupper(std::locale) checks if a character is classified as uppercase by a locale
                        (function template)
   iswupper checks if a wide character is an uppercase character
                        (function)
   C documentation for
   isupper
        ASCII values characters iscntrl isprint isspace isblank isgraph ispunct isalnum isalpha isupper islower isdigit isxdigit decimal hexadecimal octal iswcntrl iswprint iswspace iswblank iswgraph iswpunct iswalnum iswalpha iswupper iswlower iswdigit iswxdigit 0–8 \x0–\x8 \0–\10 control codes ≠0 0 0 0 0 0 0 0 0 0 0 0
                        (NUL, etc.) 9 \x9 \11 tab (\t) ≠0 0 ≠0 ≠0 0 0 0 0 0 0 0 0
                        whitespaces 10–13 \xA–\xD \12–\15 (\n, \v, \f, ≠0 0 ≠0 0 0 0 0 0 0 0 0 0
                        \r) 14–31 \xE–\x1F \16–\37 control codes ≠0 0 0 0 0 0 0 0 0 0 0 0 32 \x20 \40 space 0 ≠0 ≠0 ≠0 0 0 0 0 0 0 0 0 33–47 \x21–\x2F \41–\57 !"#$%&'()*+,-./ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0 48–57 \x30–\x39 \60–\71 0123456789 0 ≠0 0 0 ≠0 0 ≠0 0 0 0 ≠0 ≠0 58–64 \x3A–\x40 \72–\100 :;<=>?@ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0 65–70 \x41–\x46 \101–\106 ABCDEF 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 ≠0 71–90 \x47–\x5A \107–\132 GHIJKLMNOP 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 0
                        QRSTUVWXYZ 91–96 \x5B–\x60 \133–\140 [\]^_` 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0 97–102 \x61–\x66 \141–\146 abcdef 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 ≠0 103–122 \x67–\x7A \147–\172 ghijklmnop 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 0
                        qrstuvwxyz 123–126 \x7B–\x7E \172–\176 {|}~ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0 127 \x7F \177 backspace ≠0 0 0 0 0 0 0 0 0 0 0 0
                        character (DEL)