NAME
getprotoent_r, getprotobyname_r, getprotobynumber_r - get protocol
entry (reentrant)
SYNOPSIS
#include <netdb.h>
int getprotoent_r(struct protoent *result_buf, char *buf,
size_t buflen, struct protoent **result);
int getprotobyname_r(const char *name,
struct protoent *result_buf, char *buf,
size_t buflen, struct protoent **result);
int getprotobynumber_r(int proto,
struct protoent *result_buf, char *buf,
size_t buflen, struct protoent **result);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getprotoent_r(), getprotobyname_r(), getprotobynumber_r(): _BSD_SOURCE
|| _SVID_SOURCE
DESCRIPTION
The getprotoent_r(), getprotobyname_r(), and getprotobynumber_r()
functions 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 differences 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
returned protoent 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 protocol 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
number is returned.
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).
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 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 <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, s;
struct protoent result_buf;
struct protoent *result;
char buf[MAX_BUF];
char **p;
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 (p = result_buf.p_aliases; *p != NULL; p++)
printf("%s ", *p);
printf("\n");
exit(EXIT_SUCCESS);
}
SEE ALSO
getprotoent(3), protocols(5)
COLOPHON
This page is part of release 3.24 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/.