#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():
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.
On error, record not found (getprotobyname_r(), getprotobynumber_r()), or end of input (getprotoent_r()) result is set to NULL.
$ ./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
#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);
}