What is the maximum allowed files open?

Is 1048577 the limit of open files in Ubuntu? If I try the following code it works.

However, if I change the value to 1048578 the setrlimit function will return the code 1 and errno will be set to 1 as well.

int l;
struct rlimit rl;

rl.rlim_cur = 1048577;
rl.rlim_max = 1048577;

l = setrlimit(RLIMIT_NOFILE, &rl);

if(l != 0){
    errx(1, "setrlimit returned result %d", errno);
}

I am running it as root and compiling with GCC 4.6.3