std::iscntrl (3) - Linux Man Pages

std::iscntrl: std::iscntrl

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 <iostream>
  #include <cctype>
  #include <clocale>


  int main()
  {
      unsigned char c = '\x94'; // the control code CCH in ISO-8859-1


      std::cout << "iscntrl(\'\\x94\', default C locale) returned "
                 << std::boolalpha << (bool)std::iscntrl(c) << '\n';


      std::setlocale(LC_ALL, "en_GB.iso88591");
      std::cout << "iscntrl(\'\\x94\', ISO-8859-1 locale) returned "
                << std::boolalpha << (bool)std::iscntrl(c) << '\n';


  }

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 locale
iscntrl(std::locale) (function template)
                     checks if a wide character is a control character
iswcntrl (function)


ASCII values iscntrl isprint isspace isblank isgraph ispunct isalnum isalpha isupper islower isdigit isxdigit
decimal hexadecimal octal characters iswcntrl iswprint iswspace iswblank iswgraph iswpunct iswalnum iswalpha iswupper iswlower iswdigit iswxdigit


0–8 \x0–\x8 \0–\10 control codes (NUL, etc.) ≠0 0 0 0 0 0 0 0 0 0 0 0
9 \x9 \11 tab (\t) ≠0 0 ≠0 ≠0 0 0 0 0 0 0 0 0
10–13 \xA–\xD \12–\15 whitespaces (\n, \v, \f, \r) ≠0 0 ≠0 0 0 0 0 0 0 0 0 0
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–\10ABCDEF 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 ≠0
71–90 \x47–\x5A \107–\13GHIJKLMNOP 0 ≠0 0 0 ≠0 0 ≠0 ≠0 ≠0 0 0 0
                              QRSTUVWXYZ
91–96 \x5B–\x60 \133–\14[\]^_` 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
97–102\x61–\x66 \141–\14abcdef 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 ≠0
103–12\x67–\x7A \147–\17ghijklmnop 0 ≠0 0 0 ≠0 0 ≠0 ≠0 0 ≠0 0 0
                              qrstuvwxyz
123–12\x7B–\x7E \172–\17{|}~ 0 ≠0 0 0 ≠0 ≠0 0 0 0 0 0 0
127 \x7F \177 backspace character (DEL) ≠0 0 0 0 0 0 0 0 0 0 0 0