gethostbyname(3) Library Functions Manual gethostbyname(3)
NAME
gethostbyname, gethostbyname_r - Get a network host entry by name
LIBRARY
Standard C Library (libc.so, libc.a)
SYNOPSIS
#include <netdb.h>
struct hostent *gethostbyname( const char *name);
[Tru64 UNIX] The following function is supported in order to maintain backward compatibility with previous versions of the operating sys-
tem. You should not use it in new designs. int gethostbyname_r( const char *name, struct hostent *hptr, struct hos-
tent_data *hdptr);
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
gethostbyname(): XNS4.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Specifies the official network name or alias. [Tru64 UNIX] For gethostbyname_r() only, this points to the hostent structure. The netdb.h
header file defines hostent structure. [Tru64 UNIX] For gethostbyname_r() only, this is data for hosts database. The netdb.h header file
defines hostent_data structure.
DESCRIPTION
The gethostbyname() function returns a pointer to a structure of type hostent. Its members specify data obtained from either the local
/etc/hosts file or one of the files distributed by DNS/BIND or NIS. To determine which file or files to search, and in which order, the
system uses the switches in the /etc/svc.conf file. The netdb.h header file defines the hostent structure.
If using DNS/BIND, the information is obtained from a name server specified in the /etc/resolv.conf file.
If the name parameter does not contain a dot "." and you are using DNS/BIND, the gethostbyname() function checks whether the environment
variable HOSTALIASES is set. If set, it first searches the file named by HOSTALIASES for an alias matching the name parameter. The alias
file has the following format: name1 name2 The alias name. This name cannot include dots. The host name used by DNS/BIND to look up the
host information. The hosts database must be distributed by DNS/BIND.
NOTES
The gethostbyname() function returns a pointer to thread-specific data. Subsequent calls to this or a related function from the same
thread overwrite this data.
[Tru64 UNIX] The gethostbyname_r() function is an obsolete reentrant version of the gethostbyname() function. It is supported in order to
maintain backward compatibility with previous versions of the operating system and should not be used in new designs. Note that you must
zero-fill the hdptr structure before its first access by the gethostbyname_r() function.
RETURN VALUES
Upon successful completion, the gethostbyname() function returns a pointer to a hostent structure. If it reaches the end of the network
host name database, it returns a null pointer.
[Tru64 UNIX] Upon successful completion, the gethostbyname_r() function stores the hostent structure in the location pointed to by hptr,
and returns a value of 0 (zero). Upon failure, it returns a value of -1.
ERRORS
If the gethostbyname() or gethostbyname_r() function call fails, h_errno is set to one of the following the values: Host is unknown. The
server recognized the request and the name, but no address is available for the name. Another type of name server request may be success-
ful. An unexpected server failure occurred. This is a nonrecoverable error. A transient error occurred, for example, the server did not
respond. A retry at some later time may be successful.
[Tru64 UNIX] If any of the following conditions occurs, the gethostbyaddr_r() function sets errno to the corresponding value: The name,
hptr, or hdptr is invalid.
FILES
The Internet network host name database. Each record in the file occupies a single line and has three fields consisting of the host
address, official host name, and aliases. The resolver configuration file. The database service selection configuration file.
RELATED INFORMATION
Functions: endhostent(3), gethostbyaddr(3), sethostent(3).
Files: hostname(5), resolv.conf(4), svc.conf(4).
Networks: bind_intro(7), nis_intro(7).
Standards: standards(5) delim off
gethostbyname(3)