title: get_nprocs() and get_nprocs_conf() -- How to do error checking
body: <p>I am using get_nproc() and get_nprocs_conf() top get number of online and all processor cores present in my machine.</p>
  
  <p>How do I check for errors with these functions. Any specific error values?
  Do they even notify of errors ? not sure.</p>
  
  <p>I would really like to check for error with the call as my program would depend on the returned values a lot.</p>
  
  <p>FYI - As these functions are available from GNU library I prefer these over 
  sysconf (_SC_NPROCESSORS_ONLN) and sysconf (_SC_NPROCESSORS_CONF)
  so basically I want to avoid including extra file </p>
  
  <p>Also, I see that these are declared in -- sys/sysinfo.h but wasn't able to find the definition. Any idea on where can I get that ?</p>