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iscntrl

Defined in header <ctype.h> 
int iscntrl( int ch );

Checks if the given character is a control character, i.e. 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.

Example

#include <stdio.h>
#include <ctype.h>
#include <locale.h>
 
int main(void)
{
    unsigned char c = '\x94'; // the control code CCH in ISO-8859-1
    printf("In the default C locale, \\x94 is %sa control character\n",
           iscntrl(c) ? "" : "not " );
    setlocale(LC_ALL, "en_GB.iso88591");
    printf("In ISO-8859-1 locale, \\x94 is %sa control character\n",
           iscntrl(c) ? "" : "not " );
}

Possible output:

In the default C locale, \x94 is not a control character
In ISO-8859-1 locale, \x94 is a control character

References

  • C17 standard (ISO/IEC 9899:2018):
    • 7.4.1.4 The iscntrl function (p: 146)
  • C11 standard (ISO/IEC 9899:2011):
    • 7.4.1.4 The iscntrl function (p: 201)
  • C99 standard (ISO/IEC 9899:1999):
    • 7.4.1.4 The iscntrl function (p: 182)
  • C89/C90 standard (ISO/IEC 9899:1990):
    • 4.3.1.3 The iscntrl function

See also

(C95)
 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

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