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() functions 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 differences 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 sig-
       natures.

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]
", argv[0]);
	       exit(EXIT_FAILURE);
	   }

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

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

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

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

	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       getprotoent(3), protocols(5)

COLOPHON

       This  page is part of release 3.27 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)