|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | EXAMPLES | SEE ALSO | COLOPHON |
|
|
|
getprotoent_r(3) Library Functions Manual getprotoent_r(3)
getprotoent_r, getprotobyname_r, getprotobynumber_r - get protocol
entry (reentrant)
Standard C library (libc, -lc)
#include <netdb.h>
int getprotoent_r(size_t size;
struct protoent *restrict result_buf,
char buf[restrict size], size_t size,
struct protoent **restrict result);
int getprotobyname_r(size_t size;
const char *restrict name,
struct protoent *restrict result_buf,
char buf[restrict size], size_t size,
struct protoent **restrict result);
int getprotobynumber_r(size_t size;
int proto,
struct protoent *restrict result_buf,
char buf[restrict size], size_t size,
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
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 size. 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 size 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.
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.
ENOENT (getprotoent_r()) No more records in database.
ERANGE buf is too small. Try again with a larger buffer (and
increased size).
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────────────────┬───────────────┬────────────────┐
│ Interface │ Attribute │ Value │
├───────────────────────────────┼───────────────┼────────────────┤
│ getprotoent_r(), │ Thread safety │ MT-Safe locale │
│ getprotobyname_r(), │ │ │
│ getprotobynumber_r() │ │ │
└───────────────────────────────┴───────────────┴────────────────┘
Functions with similar names exist on some other systems, though
typically with different calling signatures.
GNU.
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 size; 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) (size=78)
p_name=tcp; p_proto=6; aliases=TCP
$ ./a.out xxx 1
ERANGE! Retrying with larger buffer
getprotobyname_r() returned: 0 (success) (size=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 size, erange_cnt, s;
struct protoent result_buf;
struct protoent *result;
char buf[MAX_BUF];
if (argc < 2) {
printf("Usage: %s proto-name [size]\n", argv[0]);
exit(EXIT_FAILURE);
}
size = 1024;
if (argc > 2)
size = atoi(argv[2]);
if (size > 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, size, &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. */
size++;
if (size > MAX_BUF) {
printf("Exceeded buffer limit (%d)\n", MAX_BUF);
exit(EXIT_FAILURE);
}
}
} while (s == ERANGE);
printf("getprotobyname_r() returned: %s (size=%d)\n",
(s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
strerror(s), size);
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);
}
getprotoent(3), protocols(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-06-28 getprotoent_r(3)
Pages that refer to this page: getprotoent(3)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|