How to check if a given file descriptor stored in a variable is still valid?

Question

I have a file descriptor stored in a variable say var. How can I check whether that descriptor is valid at a later stage?

  fdvar1= open(.....);
  fdvar2 =          


        

Answer 1

You can use the fcntl() function:

int fd_is_valid(int fd)
{
    return fcntl(fd, F_GETFD) != -1 || errno != EBADF;
}