Manpage of GETPROTOENT_R

GETPROTOENT_R

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

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():
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Glibc 2.19 and earlier:
        _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 protoentstructure 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 protoentstructure as the function result, these functions copy the structure into the location pointed to by result_buf.

The bufarray is used to store the string fields pointed to by the returned protoentstructure. (The nonreentrant functions allocate these strings in static storage.) The size of this array is specified in buflen. If bufis 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 *resultis set pointing to result_buf; otherwise, *resultis 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()) resultis set to NULL.  

ERRORS

ENOENT
(getprotoent_r()) No more records in database.
ERANGE
bufis 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).
InterfaceAttributeValue
getprotoent_r(),
getprotobyname_r(),
getprotobynumber_r()
Thread safetyMT-Safe locale

 

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 1ERANGE! Retrying with larger buffer
getprotobyname_r() returned: 0 (success)  (buflen=78)
p_name=tcp; p_proto=6; aliases=TCP
$ ./a.out xxx 1ERANGE! 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)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
EXAMPLE
Program source
SEE ALSO

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