std::iscntrl

 

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isalnum isalpha islower isupper isdigit isxdigit	isblank (C++11) iscntrl isgraph isspace isprint ispunct
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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 unsignedchar 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 unsignedchar nor equal to EOF. To use these functions safely with plain chars (or signedchars), the argument should first be converted to unsignedchar:

bool my_iscntrl(char ch){return std::iscntrl(static_cast<unsignedchar>(ch));}

Similarly, they should not be directly used with standard algorithms when the iterator's value type is char or signedchar. Instead, convert the value to unsignedchar first:

int count_cntrls(conststd::string& s){returnstd::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[](unsignedchar c){return std::iscntrl(c);}// correct);}

Example

Run this code

#include <cctype>#include <clocale>#include <iostream>   int main(){unsignedchar 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

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

ASCII values			characters	iscntrl iswcntrl	isprint iswprint	isspace iswspace	isblank iswblank	isgraph iswgraph	ispunct iswpunct	isalnum iswalnum	isalpha iswalpha	isupper iswupper	islower iswlower	isdigit iswdigit	isxdigit iswxdigit
decimal	hexadecimal	octal
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–\106	ABCDEF	0	≠0	0	0	≠0	0	≠0	≠0	≠0	0	0	≠0
71–90	\x47–\x5A	\107–\132	GHIJKLMNOP QRSTUVWXYZ	0	≠0	0	0	≠0	0	≠0	≠0	≠0	0	0	0
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 qrstuvwxyz	0	≠0	0	0	≠0	0	≠0	≠0	0	≠0	0	0
123–126	\x7B–\x7E	\172–\176	{|}~	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