1GETSERVENT_R(3)            Linux Programmer's Manual           GETSERVENT_R(3)
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NAME

6       getservent_r,  getservbyname_r,  getservbyport_r  -  get  service entry
7       (reentrant)
8

SYNOPSIS

10       #include <netdb.h>
11
12       int getservent_r(struct servent *result_buf, char *buf,
13                       size_t buflen, struct servent **result);
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15       int getservbyname_r(const char *name, const char *proto,
16                       struct servent *result_buf, char *buf,
17                       size_t buflen, struct servent **result);
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19       int getservbyport_r(int port, const char *proto,
20                       struct servent *result_buf, char *buf,
21                       size_t buflen, struct servent **result);
22
23   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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25       getservent_r(), getservbyname_r(), getservbyport_r():
26           _BSD_SOURCE || _SVID_SOURCE
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DESCRIPTION

29       The getservent_r(), getservbyname_r(), and getservbyport_r()  functions
30       are  the  reentrant  equivalents  of, respectively, getservent(3), get‐
31       servbyname(3), and getservbyport(3).  They differ in the way  that  the
32       servent  structure  is  returned, and in the function calling signature
33       and return value.  This manual page describes just the differences from
34       the nonreentrant functions.
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36       Instead of returning a pointer to a statically allocated servent struc‐
37       ture as the function result, these functions copy  the  structure  into
38       the location pointed to by result_buf.
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40       The  buf  array  is  used  to store the string fields pointed to by the
41       returned servent structure.  (The nonreentrant functions allocate these
42       strings  in  static  storage.)   The size of this array is specified in
43       buflen.  If buf is too small, the call fails with the error ERANGE, and
44       the  caller  must  try again with a larger buffer.  (A buffer of length
45       1024 bytes should be sufficient for most applications.)
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47       If the function  call  successfully  obtains  a  service  record,  then
48       *result  is  set  pointing  to result_buf; otherwise, *result is set to
49       NULL.
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RETURN VALUE

52       On success, these functions return 0.  On error, they return one of the
53       positive error numbers listed in errors.
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55       On  error,  record not found (getservbyname_r(), getservbyport_r()), or
56       end of input (getservent_r()) result is set to NULL.
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ERRORS

59       ENOENT (getservent_r()) No more records in database.
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61       ERANGE buf is too small.  Try again with a larger buffer (and increased
62              buflen).
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CONFORMING TO

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

70       The program below uses getservbyport_r() to retrieve the service record
71       for the port and protocol named in its first command-line argument.  If
72       a  third (integer) command-line argument is supplied, it is used as the
73       initial value for buflen; if getservbyport_r()  fails  with  the  error
74       ERANGE,  the  program  retries with larger buffer sizes.  The following
75       shell session shows a couple of sample runs:
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77           $ ./a.out 7 tcp 1
78           ERANGE! Retrying with larger buffer
79           getservbyport_r() returned: 0 (success)  (buflen=87)
80           s_name=echo; s_proto=tcp; s_port=7; aliases=
81           $ ./a.out 77777 tcp
82           getservbyport_r() returned: 0 (success)  (buflen=1024)
83           Call failed/record not found
84
85   Program source
86
87       #define _GNU_SOURCE
88       #include <ctype.h>
89       #include <netdb.h>
90       #include <stdlib.h>
91       #include <stdio.h>
92       #include <errno.h>
93       #include <string.h>
94
95       #define MAX_BUF 10000
96
97       int
98       main(int argc, char *argv[])
99       {
100           int buflen, erange_cnt, port, s;
101           struct servent result_buf;
102           struct servent *result;
103           char buf[MAX_BUF];
104           char *protop;
105           char **p;
106
107           if (argc < 3) {
108               printf("Usage: %s port-num proto-name [buflen]\n", argv[0]);
109               exit(EXIT_FAILURE);
110           }
111
112           port = htons(atoi(argv[1]));
113           protop = (strcmp(argv[2], "null") == 0 ||
114                  strcmp(argv[2], "NULL") == 0) ?  NULL : argv[2];
115
116           buflen = 1024;
117           if (argc > 3)
118               buflen = atoi(argv[3]);
119
120           if (buflen > MAX_BUF) {
121               printf("Exceeded buffer limit (%d)\n", MAX_BUF);
122               exit(EXIT_FAILURE);
123           }
124
125           erange_cnt = 0;
126           do {
127               s = getservbyport_r(port, protop, &result_buf,
128                            buf, buflen, &result);
129               if (s == ERANGE) {
130                   if (erange_cnt == 0)
131                       printf("ERANGE! Retrying with larger buffer\n");
132                   erange_cnt++;
133
134                   /* Increment a byte at a time so we can see exactly
135                      what size buffer was required */
136
137                   buflen++;
138
139                   if (buflen > MAX_BUF) {
140                       printf("Exceeded buffer limit (%d)\n", MAX_BUF);
141                       exit(EXIT_FAILURE);
142                   }
143               }
144           } while (s == ERANGE);
145
146           printf("getservbyport_r() returned: %s  (buflen=%d)\n",
147                   (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
148                   strerror(s), buflen);
149
150           if (s != 0 || result == NULL) {
151               printf("Call failed/record not found\n");
152               exit(EXIT_FAILURE);
153           }
154
155           printf("s_name=%s; s_proto=%s; s_port=%d; aliases=",
156                       result_buf.s_name, result_buf.s_proto,
157                       ntohs(result_buf.s_port));
158           for (p = result_buf.s_aliases; *p != NULL; p++)
159               printf("%s ", *p);
160           printf("\n");
161
162           exit(EXIT_SUCCESS);
163       }
164

SEE ALSO

166       getservent(3), services(5)
167

COLOPHON

169       This page is part of release 3.53 of the Linux  man-pages  project.   A
170       description  of  the project, and information about reporting bugs, can
171       be found at http://www.kernel.org/doc/man-pages/.
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175GNU                               2010-09-10                   GETSERVENT_R(3)
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