How to test if a C program on Linux is running from a TTY or not.

#include <stdio.h>
#include <poll.h>
#include <unistd.h>
 
int main(int argc, char* argv[]){
 
        struct pollfd fds[1] = {{.fd = STDIN_FILENO, .events = POLLIN}};
 
        if (!poll(fds, sizeof(fds) / sizeof(struct pollfd), 0)) {
                printf("Running from a TTY\n");
        } else {
                printf("NO TTY.\n");
        }
    return 0;
}

┌──(john㉿DESKTOP-PF01IEE)-[~/Documents]
└─$ ./a.out 
Running from a TTY

┌──(john㉿DESKTOP-PF01IEE)-[~/Documents]
└─$ nohup ./a.out hi
nohup: ignoring input and appending output to 'nohup.out'
 
┌──(john㉿DESKTOP-PF01IEE)-[~/Documents]
└─$ cat nohup.out 
NO TTY.