Provided by: manpages-dev_4.15-1_all 
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():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_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
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 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
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, 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.
ERRORS
ENOENT (getservent_r()) No more records in database.
ERANGE buf is too small. Try again with a larger buffer (and increased buflen).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌───────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├───────────────────┼───────────────┼────────────────┤
│getservent_r(), │ Thread safety │ MT-Safe locale │
│getservbyname_r(), │ │ │
│getservbyport_r() │ │ │
└───────────────────┴───────────────┴────────────────┘
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 4.15 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 https://www.kernel.org/doc/man-pages/.