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SuSE 11.3 - man page for getservent_r (suse section 3)

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

NAME
       getservent_r, getservbyname_r, getservbyport_r - get service entry (reentrant)

SYNOPSIS
       #include <netdb.h>

       int getservent_r(struct servent *result_buf, char *buf,
		       size_t buflen, struct servent **result);

       int getservbyname_r(const char *name, const char *proto,
		       struct servent *result_buf, char *buf,
		       size_t buflen, struct servent **result);

       int getservbyport_r(int port, const char *proto,
		       struct servent *result_buf, char *buf,
		       size_t buflen, struct servent **result);

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

       getservent_r(), getservbyname_r(), getservbyport_r(): _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       The  getservent_r(),  getservbyname_r(), and getservbyport_r() functions are the reentrant
       equivalents of, respectively, getservent(3), getservbyname(3), and getservbyport(3).  They
       differ in the way that the servent structure is returned, and in the function calling sig-
       nature and return value.  This manual page describes just the differences  from	the  non-
       reentrant functions.

       Instead of returning a pointer to a statically allocated servent 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 servent struc-
       ture.  (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 service 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, a positive error number is returned.

       On  error,  record not found (getservbyname_r(), getservbyport_r()), or end of input (get-
       servent_r()) result is set to NULL.

ERRORS
       ENOENT (getservent_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 sys-
       tems, though typically with different calling signatures.

EXAMPLE
       The  program  below uses getservbyport_r() to retrieve the service record for the port and
       protocol named in its first command-line argument.   If	a  third  (integer)  command-line
       argument  is  supplied,	it  is used as the initial value for buflen; if getservbyport_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 7 tcp 1
	   ERANGE! Retrying with larger buffer
	   getservbyport_r() returned: 0 (success)  (buflen=87)
	   s_name=echo; s_proto=tcp; s_port=7; aliases=
	   $ ./a.out 77777 tcp
	   getservbyport_r() returned: 0 (success)  (buflen=1024)
	   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, port, s;
	   struct servent result_buf;
	   struct servent *result;
	   char buf[MAX_BUF];
	   char *protop;
	   char **p;

	   if (argc < 3) {
	       printf("Usage: %s port-num proto-name [buflen]\n", argv[0]);
	       exit(EXIT_FAILURE);
	   }

	   port = htons(atoi(argv[1]));
	   protop = (strcmp(argv[2], "null") == 0 ||
		  strcmp(argv[2], "NULL") == 0) ?  NULL : argv[2];

	   buflen = 1024;
	   if (argc > 3)
	       buflen = atoi(argv[3]);

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

	   erange_cnt = 0;
	   do {
	       s = getservbyport_r(port, protop, &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("getservbyport_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("s_name=%s; s_proto=%s; s_port=%d; aliases=",
		       result_buf.s_name, result_buf.s_proto,
		       ntohs(result_buf.s_port));
	   for (p = result_buf.s_aliases; *p != NULL; p++)
	       printf("%s ", *p);
	   printf("\n");

	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       getservent(3), services(5)

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the
       project,  and  information  about  reporting  bugs,  can  be  found   at   http://www.ker-
       nel.org/doc/man-pages/.

GNU					    2008-08-19				  GETSERVENT_R(3)


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