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C iscntrl() function

C iscntrl(int ch)

The iscntrl() function is used to check whether a character is a control character or not. The function is defined in the ctype.h header file.

Note: In computing and telecommunication, a control character or non-printing character (NPC) is a code point (a number) in a character set, that does not represent a written symbol. They are used as in-band signaling to cause effects other than the addition of a symbol to the text. All other characters are mainly printing, printable, or graphic characters, except perhaps for the "space" character.

Syntax:

int iscntrl(int argument);

iscntrl() Parameters:

Name Description Required /Optional
ch ch is a character of class cntrl in the current locale. Required

Return value from isupper()

  • The iscntrl() function returns non-zero if ch is a control character; otherwise, returns 0.

Example-1: Check control character


#include <stdio.h>
#include <ctype.h>

int main()
{
    char ch;
    ch = 'Q';
    printf("Check control character:");
    printf("\nIf %c is  cntrl character or not? %d", ch, iscntrl(ch));
    ch = ' ';
    printf("\nIf %c is  cntrl character or not? %d", ch, iscntrl(ch));
    ch = '\n';
    printf("\nIf %c is  cntrl character or not? %d", ch, iscntrl(ch));
    return 0;
}

Output:

Check control character:
If Q is  cntrl character or not? 0
If   is  cntrl character or not? 0
If
 is  cntrl character or not? 32

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What's an object file in C?

An object file is the real output from the compilation phase. It's mostly machine code, but has info that allows a linker to see what symbols are in it as well as symbols it requires in order to work. (For reference, "symbols" are basically names of global objects, functions, etc.)

A linker takes all these object files and combines them to form one executable (assuming that it can, i.e.: that there aren't any duplicate or undefined symbols). A lot of compilers will do this for you (read: they run the linker on their own) if you don't tell them to "just compile" using command-line options. (-c is a common "just compile; don't link" option.)

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