std::iscntrl(3)

NAME
std::iscntrl - std::iscntrl

Synopsis
   Defined in header <cctype>
   int iscntrl( int ch );
   Checks if the given character is a control character as classified by the currently
   installed C locale. In the default, "C" locale, the control characters are the
   characters with the codes 0x00-0x1F and 0x7F.
   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 a control character, zero otherwise.

Notes
   Like all other functions from <cctype>, the behavior of std::iscntrl 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_iscntrl(char ch)
 {
     return std::iscntrl(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_cntrls(const std::string& s)
 {
     return std::count_if(s.begin(), s.end(),
                       // static_cast<int(*)(int)>(std::iscntrl) // wrong
                       // [](int c){ return std::iscntrl(c); } // wrong
                       // [](char c){ return std::iscntrl(c); } // wrong
                        [](unsigned char c){ return std::iscntrl(c); } // correct
                        );
 }

Example
// Run this code
 #include <cctype>
 #include <clocale>
 #include <iostream>
 int main()
 {
     unsigned char c = '\x94'; // the control code CCH in ISO-8859-1
     std::cout << "iscntrl(\'\\x94\', default C locale) returned "
               << std::boolalpha << !!std::iscntrl(c) << '\n';
     std::setlocale(LC_ALL, "en_GB.iso88591");
     std::cout << "iscntrl(\'\\x94\', ISO-8859-1 locale) returned "
               << !!std::iscntrl(c) << '\n';
 }

Possible output:
 iscntrl('\x94', default C locale) returned false
 iscntrl('\x94', ISO-8859-1 locale) returned true

See also
                        checks if a character is classified as a control character by a
   iscntrl(std::locale) locale
                        (function template)
   iswcntrl checks if a wide character is a control character
                        (function)
   C documentation for
   iscntrl
        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)