I have a requirement to close all the file descriptors from 3 to 1024 for a particular application.

Right now, this is how I do it ..

for ( int i = 3 ; i <= 1024; ++i )
close(i);

That's not the way it works. It is, potentially, per process. You can call getrlimit to obtain the value.

Using getrlimit and the appropriate constants, this is what I am using now.

struct rlimit RL;

getrlimit(RLIMIT_NOFILE, &RL)
  for ( int fd = 3; fd <= RL.rlim_cur; ++fd )
   close(fd);

You misunderstand. A process can call setrlimit() and reduce the number of open file desriptors allowed by the process. Or it can be reduced for all users.

The kernel on some versions of unix can be reconfigured to allow more than 1024 open file descriptors.

The point: You cannot depend on 1024

Jim,

I agree with you. And that is why, I took to getrlimit.

When I said

Apparently rlim_cur and rlim_max gives me 1024 on my machine.

I was just giving away information which was needed.

Vino