iscntrl() function in C++

In this guide, you will learn what is iscntrl() function is in C++ programming and how to use it with an example.

1. iscntrl() Function Overview

The iscntrl() function is a part of the C++ <cctype> library. This function checks if the passed character is a control character. Control characters are non-printable characters, with ASCII values between 0 to 31 and 127 (inclusive).

Signature:

int iscntrl(int ch);

Parameters:

- ch: The character to be checked. It's an int, but it is basically the ASCII value of the character.

2. Source Code Example

#include <iostream>
#include <cctype>

int main() {
    char ch1 = '\n';
    char ch2 = 'A';

    if(iscntrl(ch1)) {
        std::cout << "ch1 is a control character." << std::endl;
    } else {
        std::cout << "ch1 is not a control character." << std::endl;
    }

    if(iscntrl(ch2)) {
        std::cout << "ch2 is a control character." << std::endl;
    } else {
        std::cout << "ch2 is not a control character." << std::endl;
    }

    return 0;
}

Output:

ch1 is a control character.
ch2 is not a control character.

3. Explanation

In the example above, we've used the iscntrl() function to check whether the character is a control character or not. 

The character \n (newline) is a control character, hence for ch1, it returns true. 

However, ch2 which contains the character 'A' is not a control character, so for ch2, it returns false.