In a cpp application I am deleting a file on a partition, but space is not freeing..
 

1) deleting file using remove() call
2) no other hard link for the file
3) tried to close file descriptor using following scripts then remove() call
-------
for fd in $(ls /proc/$$/fd); do
case "$fd" in
0|1|2|255)
;;
*)
eval "exec $fd>&-"
;;
esac
done
-------

But space not freed

4) I tried with truncate() and then remove() call Now files deleted and space freed

Is it the only and right way to do this?

From the man page for remove:

I think your for cycle does not work, it is simple not possible (to close a file descriptor from outside, from another process - for example from a shell script).

There is in theory another way to do this, though I would have to dig though my notes on how to remove the flag of open files by PID. However if anything did go wrong your looking at a corrupt file table on your format. I think it might be better to trace the PID of the offending process and kill it. Barking up any other tree might just trash your entire disk.