getprotoent_r man page on ElementaryOS

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GETPROTOENT_R(3)	   Linux Programmer's Manual	      GETPROTOENT_R(3)

NAME
       getprotoent_r,  getprotobyname_r,  getprotobynumber_r  -	 get  protocol
       entry (reentrant)

SYNOPSIS
       #include <netdb.h>

       int getprotoent_r(struct protoent *result_buf, char *buf,
		       size_t buflen, struct protoent **result);

       int getprotobyname_r(const char *name,
		       struct protoent *result_buf, char *buf,
		       size_t buflen, struct protoent **result);

       int getprotobynumber_r(int proto,
		       struct protoent *result_buf, char *buf,
		       size_t buflen, struct protoent **result);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getprotoent_r(), getprotobyname_r(), getprotobynumber_r():
	   _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       The getprotoent_r(), getprotobyname_r(), and getprotobynumber_r() func‐
       tions  are  the reentrant equivalents of, respectively, getprotoent(3),
       getprotobyname(3), and getprotobynumber(3).  They  differ  in  the  way
       that  the  protoent  structure is returned, and in the function calling
       signature and return value.  This manual page describes just  the  dif‐
       ferences from the nonreentrant functions.

       Instead	of  returning  a  pointer  to  a statically allocated protoent
       structure as the function result, these functions  copy	the  structure
       into the location pointed to by result_buf.

       The  buf	 array	is  used  to store the string fields pointed to by the
       returned protoent  structure.   (The  nonreentrant  functions  allocate
       these  strings in static storage.)  The size of this array is specified
       in buflen.  If buf is too small, the call fails with the error  ERANGE,
       and  the	 caller	 must  try  again  with a larger buffer.  (A buffer of
       length 1024 bytes should be sufficient for most applications.)

       If the function call  successfully  obtains  a  protocol	 record,  then
       *result	is  set	 pointing  to result_buf; otherwise, *result is set to
       NULL.

RETURN VALUE
       On success, these functions return 0.  On error, they return one of the
       positive error numbers listed in ERRORS.

       On  error, record not found (getprotobyname_r(), getprotobynumber_r()),
       or end of input (getprotoent_r()) result is set to NULL.

ERRORS
       ENOENT (getprotoent_r()) No more records in database.

       ERANGE buf is too small.	 Try again with a larger buffer (and increased
	      buflen).

CONFORMING TO
       These functions are GNU extensions.  Functions with similar names exist
       on some other systems, though typically with different  calling	signa‐
       tures.

EXAMPLE
       The  program  below  uses  getprotobyname_r()  to retrieve the protocol
       record for the protocol named in its first command-line argument.  If a
       second  (integer)  command-line argument is supplied, it is used as the
       initial value for buflen; if getprotobyname_r() fails  with  the	 error
       ERANGE,	the  program  retries with larger buffer sizes.	 The following
       shell session shows a couple of sample runs:

	   $ ./a.out tcp 1
	   ERANGE! Retrying with larger buffer
	   getprotobyname_r() returned: 0 (success)  (buflen=78)
	   p_name=tcp; p_proto=6; aliases=TCP
	   $ ./a.out xxx 1
	   ERANGE! Retrying with larger buffer
	   getprotobyname_r() returned: 0 (success)  (buflen=100)
	   Call failed/record not found

   Program source

       #define _GNU_SOURCE
       #include <ctype.h>
       #include <netdb.h>
       #include <stdlib.h>
       #include <stdio.h>
       #include <errno.h>
       #include <string.h>

       #define MAX_BUF 10000

       int
       main(int argc, char *argv[])
       {
	   int buflen, erange_cnt, s;
	   struct protoent result_buf;
	   struct protoent *result;
	   char buf[MAX_BUF];
	   char **p;

	   if (argc < 2) {
	       printf("Usage: %s proto-name [buflen]\n", argv[0]);
	       exit(EXIT_FAILURE);
	   }

	   buflen = 1024;
	   if (argc > 2)
	       buflen = atoi(argv[2]);

	   if (buflen > MAX_BUF) {
	       printf("Exceeded buffer limit (%d)\n", MAX_BUF);
	       exit(EXIT_FAILURE);
	   }

	   erange_cnt = 0;
	   do {
	       s = getprotobyname_r(argv[1], &result_buf,
			    buf, buflen, &result);
	       if (s == ERANGE) {
		   if (erange_cnt == 0)
		       printf("ERANGE! Retrying with larger buffer\n");
		   erange_cnt++;

		   /* Increment a byte at a time so we can see exactly
		      what size buffer was required */

		   buflen++;

		   if (buflen > MAX_BUF) {
		       printf("Exceeded buffer limit (%d)\n", MAX_BUF);
		       exit(EXIT_FAILURE);
		   }
	       }
	   } while (s == ERANGE);

	   printf("getprotobyname_r() returned: %s  (buflen=%d)\n",
		   (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
		   strerror(s), buflen);

	   if (s != 0 || result == NULL) {
	       printf("Call failed/record not found\n");
	       exit(EXIT_FAILURE);
	   }

	   printf("p_name=%s; p_proto=%d; aliases=",
		       result_buf.p_name, result_buf.p_proto);
	   for (p = result_buf.p_aliases; *p != NULL; p++)
	       printf("%s ", *p);
	   printf("\n");

	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       getprotoent(3), protocols(5)

COLOPHON
       This page is part of release 3.54 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  2010-09-10		      GETPROTOENT_R(3)
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