zkNetdb.h is a portable wrapper for the POSIX header <netdb.h>. It is part of the libzk library because <netdb.h> doesn't exist in Standard C.

zkNetdb.h - Supported Macros from <netdb.h>
Macro Description
HOST_NOT_FOUND Error value for zkGethostbyname and zkGethostbyaddr.
NO_DATA Error value for zkGethostbyname and zkGethostbyaddr.
NO_RECOVERY Error value for zkGethostbyname and zkGethostbyaddr.
TRY_AGAIN Error value for zkGethostbyname and zkGethostbyaddr.

zkNetdb.h - Supported Types from <netdb.h>
Type Description
struct hostent, with members:  
char*  h_name
 
char** h_aliases
 
int    h_addrtype
 
int    h_length
 
char** h_addr_list
 
struct protoent, with members:  
char*  p_name
 
char** p_aliases
 
int    p_proto
 
struct servent, with members:  
char*  s_name
 
char** s_aliases
 
int    s_port
 
char*  s_proto
 

zkNetdb.h - Deprecated Functions from <netdb.h>
Don't Call This Instead, Call This Reason
gethostbyaddr zkGethostbyaddr Not in Standard C.
gethostbyname zkGethostbyname Not in Standard C.
getprotobyname zkGetprotobyname Not in Standard C.
getprotobynumber zkGetprotobynumber Not in Standard C.
getservbyname zkGetservbyname Not in Standard C.
getservbyport zkGetservbyport Not in Standard C.

zkNetdb.h - Deprecated Variables from <netdb.h>
Don't Use This Instead, Use This Reason
h_errno zkHErrno() Not in Standard C, plus it isn't reentrant.