#  You need EOF on input...
system("nohup program </dev/null >/dev/null 2>&1 &");
#  You need 1 line of empty input...
system("/bin/echo | nohup program >/dev/null 2>&1 &");
#  You need infinite lines of empty input
system("yes '' | nohup program >/dev/null 2>&1 &");