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getnetent(3c)
getnetbyname(3C) Standard C Library Functions getnetbyname(3C)
NAME
getnetbyname, getnetbyname_r, getnetbyaddr, getnetbyaddr_r, getnetent,
getnetent_r, setnetent, endnetent - get network entry
SYNOPSIS
#include <netdb.h>
struct netent *getnetbyname(const char *name);
struct netent *getnetbyname_r(const char *name, struct netent *result,
char *buffer, int buflen);
struct netent *getnetbyaddr(in_addr_t net, int type);
struct netent *getnetbyaddr_r(long net, int type, struct netent *result,
char *buffer, int buflen);
struct netent *getnetent(void);
struct netent *getnetent_r(struct netent *result, char *buffer,
int buflen);
int setnetent(int stayopen);
int endnetent(void);
DESCRIPTION
These functions are used to obtain entries for IPv4 networks. An entry
may come from any of the sources for networks specified in the nss‐
witch.conf(5) configuration.
getnetbyname() searches for a network entry with the network name spec‐
ified by the character string parameter name.
getnetbyaddr() searches for a network entry with the network address
specified by net. The parameter type specifies the family of the ad‐
dress. This should be one of the address families defined in
<sys/socket.h>. See the NOTES section below for more information.
Network numbers and local address parts are returned as machine format
integer values, that is, in host byte order. See also inet(3C).
The netent.n_net member in the netent structure pointed to by the re‐
turn value of the above functions is calculated by inet_network(). The
inet_network() function returns a value in host byte order that is
aligned based upon the input string. For example:
tab(); lw(2.75i) lw(2.75i) lw(2.75i) lw(2.75i) TextValue "10"0x0000000a
"10.0"0x00000a00 "10.0.1"0a000a0001 "10.0.1.28"0x0a000180
Commonly, the alignment of the returned value is used as a crude ap‐
proximate of pre-CIDR (Classless Inter-Domain Routing) subnet mask. For
example:
in_addr_t addr, mask;
addr = inet_network(net_name);
mask= ~(in_addr_t)0;
if ((addr & IN_CLASSA_NET) == 0)
addr <<= 8, mask <<= 8;
if ((addr & IN_CLASSA_NET) == 0)
addr <<= 8, mask <<= 8;
if ((addr & IN_CLASSA_NET) == 0)
addr <<= 8, mask <<= 8;
This usage is deprecated by the CIDR requirements. See RFC 1519, Class‐
less Inter-Domain Routing (CIDR): an Address Assignment and Aggregation
Strategy.
The functions setnetent(), getnetent(), and endnetent() are used to
enumerate network entries from the database.
setnetent() sets (or resets) the enumeration to the beginning of the
set of network entries. This function should be called before the first
call to getnetent(). Calls to getnetbyname() and getnetbyaddr() leave
the enumeration position in an indeterminate state. If the stayopen
flag is non-zero, the system may keep allocated resources such as open
file descriptors until a subsequent call to endnetent().
Successive calls to getnetent() return either successive entries or
NULL, indicating the end of the enumeration.
endnetent() may be called to indicate that the caller expects to do no
further network entry retrieval operations; the system may then deallo‐
cate resources it was using. It is still allowed, but possibly less ef‐
ficient, for the process to call more network entry retrieval functions
after calling endnetent().
Reentrant Interfaces
The functions getnetbyname(), getnetbyaddr(), and getnetent() use sta‐
tic storage that is reused in each call, making these routines unsafe
for use in multi-threaded applications.
The functions getnetbyname_r(), getnetbyaddr_r(), and getnetent_r()
provide reentrant interfaces for these operations.
Each reentrant interface performs the same operation as its non-reen‐
trant counterpart, named by removing the "_r" suffix. The reentrant in‐
terfaces, however, use buffers supplied by the caller to store returned
results, and are safe for use in both single-threaded and multi-
threaded applications.
Each reentrant interface takes the same parameters as its non-reentrant
counterpart, as well as the following additional parameters. The para‐
meter result must be a pointer to a struct netent structure allocated
by the caller. On successful completion, the function returns the net‐
work entry in this structure. The parameter buffer must be a pointer to
a buffer supplied by the caller. This buffer is used as storage space
for the network entry data. All of the pointers within the returned
struct netent result point to data stored within this buffer. See RE‐
TURN VALUES. The buffer must be large enough to hold all of the data
associated with the network entry. The parameter buflen should give the
size in bytes of the buffer indicated by buffer.
For enumeration in multi-threaded applications, the position within the
enumeration is a process-wide property shared by all threads. setne‐
tent() may be used in a multi-threaded application but resets the enu‐
meration position for all threads. If multiple threads interleave calls
to getnetent_r(), the threads will enumerate disjointed subsets of the
network database.
Like their non-reentrant counterparts, getnetbyname_r() and getnet‐
byaddr_r() leave the enumeration position in an indeterminate state.
RETURN VALUES
Network entries are represented by the struct netent structure defined
in <netdb.h>.
The functions getnetbyname(), getnetbyname_r, getnetbyaddr, and getnet‐
byaddr_r() each return a pointer to a struct netent if they success‐
fully locate the requested entry; otherwise they return NULL.
The functions getnetent() and getnetent_r() each return a pointer to a
struct netent if they successfully enumerate an entry; otherwise they
return NULL, indicating the end of the enumeration.
The functions getnetbyname(), getnetbyaddr(), and getnetent() use sta‐
tic storage, so returned data must be copied before a subsequent call
to any of these functions if the data is to be saved.
When the pointer returned by the reentrant functions getnetbyname_r(),
getnetbyaddr_r(), and getnetent_r() is non-NULL, it is always equal to
the result pointer that was supplied by the caller.
The functions setnetent() and endnetent() return 0 on success.
ERRORS
The reentrant functions getnetbyname_r(), getnetbyaddr_r and getne‐
tent_r() will return NULL and set errno to ERANGE if the length of the
buffer supplied by caller is not large enough to store the result. See
Intro(2) for the proper usage and interpretation of errno in multi-
threaded applications.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelMT-Safe
SEE ALSO
Intro(2), byteorder(3C), inet(3C), netdb.h(3HEAD), Intro(3), net‐
works(5), nsswitch.conf(5), attributes(7)
Fuller, V., Li, T., Yu, J., and Varadhan, K. RFC 1519, Classless Inter-
Domain Routing (CIDR): an Address Assignment and Aggregation Strategy.
Network Working Group. September 1993.
https://tools.ietf.org/html/rfc1519.
WARNINGS
The reentrant interfaces getnetbyname_r(), getnetbyaddr_r(), and getne‐
tent_r() are included in this release on an uncommitted basis only, and
are subject to change or removal in future minor releases.
NOTES
The current implementation of these functions only return or accept
network numbers for the IPv4 Internet address family (type AF_INET).
The functions described in inet(3C) may be helpful in constructing and
manipulating addresses and network numbers in this form.
Use of the enumeration interfaces getnetent() and getnetent_r() is dis‐
couraged; enumeration may not be supported for all database sources.
The semantics of enumeration are discussed further in nsswitch.conf(5).
HISTORY
The reentrant interfaces getnetbyname_r(), getnetbyaddr_r(), and getne‐
tent_r() were added to Oracle Solaris in the Solaris 2.3 release.
The functions getnetbyname(), getnetbyaddr(), getnetent(), setnetent(),
and endnetent() have been present since the initial release of Solaris.
Oracle Solaris 11.4 6 Oct 2022 getnetbyname(3C)