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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),  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 nonreentrant 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 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 num-
       ber is returned.

       On error, record not found (getservbyname_r(),  getservbyport_r()),  or
       end of input (getservent_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  systems,  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.kernel.org/doc/man-pages/.

GNU                               2008-08-19                   GETSERVENT_R(3)
 

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Gedruckt am: 15.12.2017 18:47 GMT+0100 (2017-12-15T18:47:10+01:00)