yp_errno() returns the error code of the previous operation.
Possible errors are:
| 1 args to function are bad | 
| 2 RPC failure - domain has been unbound | 
| 3 can't bind to server on this domain | 
| 4 no such map in server's domain | 
| 5 no such key in map | 
| 6 internal yp server or client error | 
| 7 resource allocation failure | 
| 8 no more records in map database | 
| 9 can't communicate with portmapper | 
| 10 can't communicate with ypbind | 
| 11 can't communicate with ypserv | 
| 12 local domain name not set | 
| 13 yp database is bad | 
| 14 yp version mismatch | 
| 15 access violation | 
| 16 database busy | 
See also yp_err_string().