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, isupper returns a nonzero
   value only for the uppercase letters (ABCDEFGHIJKLMNOPQRSTUVWXYZ).
   If isupper returns a nonzero value, it is guaranteed that iscntrl, isdigit, ispunct,
   and 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 <iostream>
 #include <cctype>
 #include <clocale>
 int main()
 {
     unsigned char c = '\xc6'; // letter Ã† 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';
 }

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)
          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 0â€“8 \x0â€“\x8 \0â€“\10 control codes â‰ 0 0 0 0 0 0 0 0 0 0 0 0
                        (NUL, etc.) 9 \x9 \11 tab (\t) â‰ 0 0 â‰ 0 â‰ 0 0 0 0 0 0 0 0 0
                        whitespaces 10â€“13 \xAâ€“\xD \12â€“\15 (\n, \v, \f, â‰ 0 0 â‰ 0 0 0 0 0 0 0 0 0 0
                        \r) 14â€“31 \xEâ€“\x1F \16â€“\37 control codes â‰ 0 0 0 0 0 0 0 0 0 0 0 0 32 \x20 \40 space 0 â‰ 0 â‰ 0 â‰ 0 0 0 0 0 0 0 0 0 33â€“47 \x21â€“\x2F \41â€“\57 !"#$%&'()*+,-./ 0 â‰ 0 0 0 â‰ 0 â‰ 0 0 0 0 0 0 0 48â€“57 \x30â€“\x39 \60â€“\71 0123456789 0 â‰ 0 0 0 â‰ 0 0 â‰ 0 0 0 0 â‰ 0 â‰ 0 58â€“64 \x3Aâ€“\x40 \72â€“\100 :;<=>?@ 0 â‰ 0 0 0 â‰ 0 â‰ 0 0 0 0 0 0 0 65â€“70 \x41â€“\x46 \101â€“\106 ABCDEF 0 â‰ 0 0 0 â‰ 0 0 â‰ 0 â‰ 0 â‰ 0 0 0 â‰ 0 71â€“90 \x47â€“\x5A \107â€“\132 GHIJKLMNOP 0 â‰ 0 0 0 â‰ 0 0 â‰ 0 â‰ 0 â‰ 0 0 0 0
                        QRSTUVWXYZ 91â€“96 \x5Bâ€“\x60 \133â€“\140 [\]^_` 0 â‰ 0 0 0 â‰ 0 â‰ 0 0 0 0 0 0 0 97â€“102 \x61â€“\x66 \141â€“\146 abcdef 0 â‰ 0 0 0 â‰ 0 0 â‰ 0 â‰ 0 0 â‰ 0 0 â‰ 0 103â€“122 \x67â€“\x7A \147â€“\172 ghijklmnop 0 â‰ 0 0 0 â‰ 0 0 â‰ 0 â‰ 0 0 â‰ 0 0 0
                        qrstuvwxyz 123â€“126 \x7Bâ€“\x7E \172â€“\176 {|}~ 0 â‰ 0 0 0 â‰ 0 â‰ 0 0 0 0 0 0 0 127 \x7F \177 backspace â‰ 0 0 0 0 0 0 0 0 0 0 0 0
                        character (DEL)