PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       endprotoent,  getprotobyname,  getprotobynumber,  getprotoent,  setprotoent  —  network protocol database
       functions

SYNOPSIS

       #include <netdb.h>

       void endprotoent(void);
       struct protoent *getprotobyname(const char *name);
       struct protoent *getprotobynumber(int proto);
       struct protoent *getprotoent(void);
       void setprotoent(int stayopen);

DESCRIPTION

       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
       database.

       The endprotoent() function  shall  close  the  connection  to  the  database,  releasing  any  open  file
       descriptor.

       These functions need not be thread-safe.

RETURN VALUE

       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 returned.

       The  application  shall  not modify the structure to which the return value points, nor any storage areas
       pointed to by pointers within the structure. The returned pointer, and  pointers  within  the  structure,
       might  be  invalidated or the structure or the storage areas might be overwritten by a subsequent call to
       getprotobyname(), getprotobynumber(), or getprotoent().  The returned pointer, and  pointers  within  the
       structure, might also be invalidated if the calling thread is terminated.

ERRORS

       No errors are defined.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       The Base Definitions volume of POSIX.1‐2017, <netdb.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .