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

       getservent_r,  getservbyname_r,	getservbyport_r	 -  get	 service entry

       #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 ||

       The  getservent_r(), getservbyname_r(), and getservbyport_r() functions
       are the reentrant equivalents  of,  respectively,  getservent(3),  get‐
       servbyname(3),  and  getservbyport(3).  They differ in the way that the
       servent structure is returned, and in the  function  calling  signature
       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 struc‐
       ture  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  structure.   (The  non-reentrant  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

       On  success, these functions return 0.  On error, a positive error num‐
       ber is returned.

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

       ENOENT (getservent_r()) No more records in database.

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

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

       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

       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]);

	   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);

	   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");

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


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

	   printf("s_name=%s; s_proto=%s; s_port=%d; aliases=",
		       result_buf.s_name, result_buf.s_proto,
	   for (p = result_buf.s_aliases; *p != NULL; p++)
	       printf("%s ", *p);


       getservent(3), services(5)

       This  page  is  part of release 3.22 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

GNU				  2008-08-19		       GETSERVENT_R(3)

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