how to set close-on-exec by default

I'm implementing a library to run commands. The library is C, on Linux.

It currently does a popen() call to run a command and get output. The problem is that the command inherits all currently open file handlers.

If I did a fork/exec I could close the handlers in child explicitly. But that means re-implementing popen().

Can I set close-on-exec on all handlers without looping through them one by one?

Can I set close-on-exec as default for the process?

Thanks!