These routines return a protocol entry. Two types of interfaces are supported: reentrant (getprotobyname_r(), getprotobynumber_r(), and getprotoent_r()) and non-reentrant (getprotobyname(), getprotobynumber(), and getprotoent()). The reentrant routines may be used in single-threaded applications and are safe for multi-threaded applications, making them the preferred interfaces.

The reentrant routines require additional parameters which are used to return results data. result is a pointer to a struct protoent structure and will be where the returned results will be stored. buffer is used as storage space for elements of the returned results. buflen is the size of buffer and should be large enough to contain all returned data. buflen must be at least 1024 bytes.

getprotobyname_r(), getprotobynumber_r(), and getprotoent_r() each return a protocol entry.

The entry may come from one of the following sources: the protocols file (see protocols(4)), the NIS maps ``protocols.byname'' and ``protocols.bynumber'', and the NIS+ table ``protocols''. The sources and their lookup order are specified in the /etc/nsswitch.conf file (see nsswitch.conf(4) for details). Some name services such as NIS will return only one name for a host, whereas others such as NIS+ or DNS will return all aliases.

getprotobyname_r() and getprotobynumber_r() sequentially search from the beginning of the file until a matching protocol name or protocol number is found, or until an EOF is encountered.

getprotobyname() and getprotobynumber() have the same functionality as getprotobyname_r() and getprotobynumber_r() except that a static buffer is used to store returned results. These routines are unsafe in a multi-threaded application.

getprotoent_r() enumerates protocol entries: successive calls to getprotoent_r() will return either successive protocol entries or NULL. Enumeration may not be supported by some sources. Note that if multiple threads call getprotoent_r(), each will retrieve a subset of the protocol database.

getprotent() has the same functionality as getprotent_r() except that a static buffer is used to store returned results. This routine is unsafe in a multi-threaded application.

setprotoent() "rewinds" to the beginning of the enumeration of protocol entries. If the stayopen flag is non-zero, resources such as open file descriptors are not deallocated after each call to getprotobynumber_r() and getprotobyname_r(). Calls to getprotobyname_r() , getprotobyname() , getprotobynumber_r() and getprotobynumber() may leave the enumeration in an indeterminate state, so setprotoent() should be called before the first getprotoent_r() or getprotoent(). Note that setprotoent() has process-wide scope, and ``rewinds'' the protocol entries for all threads calling getprotoent_r() as well as main-thread calls to getprotoent().

endprotoent() may be called to indicate that protocol processing is complete; the system may then close any open protocols file, deallocate storage, and so forth. It is legitimate, but possibly less efficient, to call more protocol routines after endprotoent().

The internal representation of a protocol entry is a protoent structure defined in <netdb.h> with the following members:

char *p_name; char **p_aliases; int p_proto;

getprotobyname_r(), getprotobyname(), getprotobynumber_r(), and getprotobynumber() return a pointer to a struct protoent if they successfully locate the requested entry; otherwise they return NULL.

getprotoent_r() and getprotoent() return a pointer to a struct protoent if they successfully enumerate an entry; otherwise they return NULL, indicating the end of the enumeration.

getprotobyname_r(), getprotobynumber_r(), and getprotoent_r() will fail if the following is true:

ERANGE

length of the buffer supplied by caller is not large enough to store the result.

/etc/protocols

/etc/nsswitch.conf

See attributes(5) for descriptions of the following attributes:

intro(3), nsswitch.conf(4), protocols(4), attributes(5), netdb(3HEAD)

Although getprotobyname_r(), getprotobynumber_r(), and getprotoent_r() are not mentioned by POSIX 1003.1c, they were added to complete the functionality provided by similar thread-safe functions.

When compiling multithreaded applications, see intro(3), Notes On Multithread Applications, for information about the use of the _REENTRANT flag.

The routines getprotobyname_r(), getprotobynumber_r(), and getprotoent_r() are reentrant and multi-thread safe. The reentrant interfaces can be used in single-threaded as well as multi-threaded applications and are therefore the preferred interfaces.

The routines getprotobyname(), getprotobyaddr(), and getprotoent() use static storage, so returned data must be copied if it is to be saved. Because of their use of static storage for returned data, these routines are not safe for multi-threaded applications.

setprotoent() and endprotoent() have process-wide scope, and are therefore not safe in multi-threaded applications.

Use of getprotoent_r() and getprotoent() is discouraged; enumeration is well-defined for the protocols file and is supported (albeit inefficiently) for NIS and NIS+, but in general may not be well-defined. The semantics of enumeration are discussed in nsswitch.conf(4).

Only the Internet protocols are currently understood.

Programs that call getprotobyname_r() or getprotobynumber_r() routines cannot be linked statically since the implementation of these routines requires dynamic linker functionality to access shared objects at run time.