C++ :: How To Write Bits To A Disk

I'm trying to write a program that writes data to a disk in C++ without caring about it's file system. Here is what I can do so far:

#include <iostream>
#include <unistd.h>
#include <fcntl.h>
using namespace std;
char buffer[] = "Wow! I'm writing this data to a disk without puttting it into a file!";
int main(){
int Disk=open("/dev/sdb",O_RDWR);
write(Disk,buffer,sizeof(buffer));
close(Disk);
return 0;}

But this program can only write ASCII characters to the disk. But what if I want to mainipulate bits on the disk, how would I do that?