Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


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():
         Since glibc 2.19:
         Glibc 2.19 and earlier:
             _BSD_SOURCE || _SVID_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 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


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


     For   an   explanation   of   the  terms  used  in  this  section,  see
     |Interface          | Attribute     | Value          |
     |getservent_r(),    | Thread safety | MT-Safe locale |
     |getservbyname_r(), |               |                |
     |getservbyport_r()  |               |                |


     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 getservby-
         port_r()   returned:   0   (success)    (buflen=87)    s_name=echo;
         s_proto=tcp;  s_port=7;  aliases=  $  ./a.out  77777 tcp getservby-
         port_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]);
         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);
         exit(EXIT_SUCCESS); }


     getservent(3), services(5)


     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at

GNU 2017-09-15 GETSERVENT_R(3)

/data/webs/external/dokuwiki/data/pages/man/getservent_r.txt · Last modified: 2019/05/17 09:47 by

Was this page helpful?-10+1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki