#include <netdb.h>
int gethostbyname_r(char *host_name,
struct hostent *hostent_struct_addr,
struct hostent_data *hostent_data_struct_addr)
#define _XOPEN_SOURCE 520
#include <netdb.h>
int gethostbyname_r(const char *host_name,
struct hostent *hostent_struct_addr,
struct hostent_data *hostent_data_struct_addr)
The gethostbyname_r() function is used to retrieve information about a host.
There are two versions of the API, as shown above. The base IBM® i API uses BSD 4.3 structures and syntax. The other uses syntax and structures compatible with the UNIX 98 programming interface specifications. You can select the UNIX 98 compatible interface with the _XOPEN_SOURCE macro.
Authorization of *R (allow access to the object) to the host aliases file specified by the hostaliases environment variable.
You also need *X authority to each directory in the path of the host aliases file.
The gethostbyname_r() function returns an integer. Possible values are:
The struct hostent denoted by hostent_struct_addr and struct hostent_datadenoted by hostent_data_struct_addr are both defined in <netdb.h>. The structure struct hostentis defined as:
struct hostent [
char *h_name;
char **h_aliases;
int h_addrtype;
int h_length;
char **h_addr_list;
];
#define h_addr h_addr_list[0]
h_name points to the character string that contains the name of the host. h_aliases is a pointer to a NULL-terminated list of pointers, each of which points to a character string that represents an alternative name for the host. h_addrtype contains the address type of the host (for example, AF_INET). h_length contains the size of an address in octets (for example, the size of an Internet address is 4 octets). h_addr_list is a pointer to a NULL-terminated list of pointers, each of which points to a network address (in network byte order) for the host.
When the gethostbyname_r() function fails, h_errno (defined in <netdb.h>) can be set to:
The host name specified by the host_name parameter was not found.
The host name is a valid name, but there is no corresponding IP address.
An unrecoverable error has occurred.
The local server did not receive a response from an authoritative server. An attempt at a later time may succeed.
When the gethostbyname_r() function fails, errno can be set to:
Permission denied. The process does not have the appropriate privileges to the host aliases file specified by the HOSTALIASES environment variable.
The hostent_data structure was not initialized with hexadecimal zeros before initial use. For corrective action, see the description for structure hostent_data.
Note: A person with a UNIX background would expect this information to exist in a file known as /etc/resolv.conf. If the IP address is found (indicating that the local network is a domain network), the gethostbyaddr_r() function will attempt to query the domain name server for information about a host. If the query fails, the information will be obtained from the local host table. If the name server IP address is not found (indicating that local network is a flat network), the local host table is used to obtain the address.
If the host information is retrieved from the domain name server, sockets converts the host name specified by the host_name parameter to ASCII before communicating with the domain name server. If the host information is retrieved from the local host table, no conversion is done on the host name specified by the host_name parameter unless the CCSID of the job is something other than 65535. In addition, host names returned in the hostent will be returned in the default CCSID of the job if they are obtained from the domain name server. For translation to occur for the host names returned in the hostent structure when they are obtained from the local host table, you must use a job CCSID of something other than 65535.