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

i solved this problem for me. i don't know whether it can be used for general purpose but for serial connections it works fine (e.g. /dev/ttyUSB0)!

struct stat s;
fstat(m_fileDescriptor, &s);

// struct stat::nlink_t   st_nlink;   ... number of hard links 
if( s.st_nlink < 1 ){
 // treat device disconnected case
}

For details see e.g. man page http://linux.die.net/man/2/fstat

Cheers, Flo