getprotoent_r(3) Library Functions Manual getprotoent_r(3)
NAME
getprotoent_r, getprotobyname_r, getprotobynumber_r - get protocol en-
try (reentrant)
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <netdb.h>
int getprotoent_r(struct protoent *restrict result_buf,
char buf[restrict .buflen], size_t buflen,
struct protoent **restrict result);
int getprotobyname_r(const char *restrict name,
struct protoent *restrict result_buf,
char buf[restrict .buflen], size_t buflen,
struct protoent **restrict result);
int getprotobynumber_r(int proto,
struct protoent *restrict result_buf,
char buf[restrict .buflen], size_t buflen,
struct protoent **restrict result);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getprotoent_r(), getprotobyname_r(), getprotobynumber_r():
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
The getprotoent_r(), getprotobyname_r(), and getprotobynumber_r() func-
tions are the reentrant equivalents of, respectively, getprotoent(3),
getprotobyname(3), and getprotobynumber(3). They differ in the way
that the protoent structure is returned, and in the function calling
signature and return value. This manual page describes just the dif-
ferences from the nonreentrant functions.
Instead of returning a pointer to a statically allocated protoent
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 re-
turned protoent structure. (The nonreentrant functions allocate these
strings in static storage.) The size of this array is specified in bu-
flen. 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 protocol record, then *re-
sult 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 (getprotobyname_r(), getprotobynumber_r()),
or end of input (getprotoent_r()) result is set to NULL.
ERRORS
ENOENT (getprotoent_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 attrib-
utes(7).
┌────────────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────┼───────────────┼────────────────┤
│ getprotoent_r(), │ Thread safety │ MT-Safe locale │
│ getprotobyname_r(), │ │ │
│ getprotobynumber_r() │ │ │
└────────────────────────────────────┴───────────────┴────────────────┘
VERSIONS
Functions with similar names exist on some other systems, though typi-
cally with different calling signatures.
STANDARDS
GNU.
EXAMPLES
The program below uses getprotobyname_r() to retrieve the protocol
record for the protocol named in its first command-line argument. If a
second (integer) command-line argument is supplied, it is used as the
initial value for buflen; if getprotobyname_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 tcp 1
ERANGE! Retrying with larger buffer
getprotobyname_r() returned: 0 (success) (buflen=78)
p_name=tcp; p_proto=6; aliases=TCP
$ ./a.out xxx 1
ERANGE! Retrying with larger buffer
getprotobyname_r() returned: 0 (success) (buflen=100)
Call failed/record not found
Program source
#define _GNU_SOURCE
#include <ctype.h>
#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_BUF 10000
int
main(int argc, char *argv[])
{
int buflen, erange_cnt, s;
struct protoent result_buf;
struct protoent *result;
char buf[MAX_BUF];
if (argc < 2) {
printf("Usage: %s proto-name [buflen]\n", argv[0]);
exit(EXIT_FAILURE);
}
buflen = 1024;
if (argc > 2)
buflen = atoi(argv[2]);
if (buflen > MAX_BUF) {
printf("Exceeded buffer limit (%d)\n", MAX_BUF);
exit(EXIT_FAILURE);
}
erange_cnt = 0;
do {
s = getprotobyname_r(argv[1], &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("getprotobyname_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("p_name=%s; p_proto=%d; aliases=",
result_buf.p_name, result_buf.p_proto);
for (char **p = result_buf.p_aliases; *p != NULL; p++)
printf("%s ", *p);
printf("\n");
exit(EXIT_SUCCESS);
}
SEE ALSO
getprotoent(3), protocols(5)
Linux man-pages 6.7 2023-10-31 getprotoent_r(3)
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