These functions shall retrieve information about protocols. This information is
considered to be stored in a database that can be accessed sequentially or
randomly. The implementation of this database is unspecified.
The setprotoent() function shall open a connection to the database, and
set the next entry to the first entry. If the stayopen argument is
non-zero, the connection to the network protocol database shall not be closed
after each call to getprotoent() (either directly, or indirectly
through one of the other getproto*() functions), and the implementation
may maintain an open file descriptor for the database.
The getprotobyname() function shall search the database from the
beginning and find the first entry for which the protocol name specified by
name matches the p_name member, opening and closing a connection
to the database as necessary.
The getprotobynumber() function shall search the database from the
beginning and find the first entry for which the protocol number specified by
proto matches the p_proto member, opening and closing a
connection to the database as necessary.
The getprotoent() function shall read the next entry of the database,
opening and closing a connection to the database as necessary.
The getprotobyname(), getprotobynumber(), and getprotoent()
functions shall each return a pointer to a protoent structure, the
members of which shall contain the fields of an entry in the network protocol
The endprotoent() function shall close the connection to the database,
releasing any open file descriptor.
These functions need not be reentrant. A function that is not required to be
reentrant is not required to be thread-safe.
Upon successful completion, getprotobyname(), getprotobynumber(),
and getprotoent() return a pointer to a protoent structure if
the requested entry was found, and a null pointer if the end of the database
was reached or the requested entry was not found. Otherwise, a null pointer is
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html