如何在C中使用Net SNMP检索OID值？

Question

我是新来的。我正在尝试使用Net-SNMP的snmpget文件检索OID并将其存储在变量中。在哪里可以指定要查询的设备的IP地址？我在哪里可以指定要查找的OID？以及如何存储OID的值？

我已经知道我的设备的IP地址和要查找的OID。

这是Net-SNMP为snmpget提供的代码：

#include <net-snmp/net-snmp-config.h>

#if HAVE_STDLIB_H
#include <stdlib.h>
#endif
#if HAVE_UNISTD_H
#include <unistd.h>
#endif
#if HAVE_STRING_H
#include <string.h>
#else
#include <strings.h>
#endif
#include <sys/types.h>
#if HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#include <stdio.h>
#include <ctype.h>
#if TIME_WITH_SYS_TIME
# include <sys/time.h>
# include <time.h>
#else
# if HAVE_SYS_TIME_H
#  include <sys/time.h>
# else
#  include <time.h>
# endif
#endif
#if HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif
#if HAVE_NETDB_H
#include <netdb.h>
#endif
#if HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif

#include <net-snmp/utilities.h>

#include <net-snmp/net-snmp-includes.h>

#define NETSNMP_DS_APP_DONT_FIX_PDUS 0

static void
optProc(int argc, char *const *argv, int opt)
{
    switch (opt) {
    case 'C':
        while (*optarg) {
            switch (*optarg++) {
            case 'f':
                netsnmp_ds_toggle_boolean(NETSNMP_DS_APPLICATION_ID, 
                      NETSNMP_DS_APP_DONT_FIX_PDUS);
                break;
            default:
                fprintf(stderr, "Unknown flag passed to -C: %c\n",
                        optarg[-1]);
                exit(1);
            }
        }
        break;
    }
}

void
usage(void)
{
    fprintf(stderr, "USAGE: snmpget ");
    snmp_parse_args_usage(stderr);
    fprintf(stderr, " OID [OID]...\n\n");
    snmp_parse_args_descriptions(stderr);
    fprintf(stderr,
            "  -C APPOPTS\t\tSet various application specific     behaviours:\n");
    fprintf(stderr,
            "\t\t\t  f:  do not fix errors and retry the request\n");
}

int
main(int argc, char *argv[])
{
    netsnmp_session session, *ss;
    netsnmp_pdu    *pdu;
    netsnmp_pdu    *response;
    netsnmp_variable_list *vars;
    int             arg;
    int             count;
    int             current_name = 0;
    char           *names[SNMP_MAX_CMDLINE_OIDS];
    oid             name[MAX_OID_LEN];
    size_t          name_length;
    int             status;
    int             failures = 0;
    int             exitval = 0;


    /*
     * get the common command line arguments 
     */
    switch (arg = snmp_parse_args(argc, argv, &session, "C:", optProc)) {
    case NETSNMP_PARSE_ARGS_ERROR:
        exit(1);
    case NETSNMP_PARSE_ARGS_SUCCESS_EXIT:
        exit(0);
    case NETSNMP_PARSE_ARGS_ERROR_USAGE:
        usage();
        exit(1);
    default:
    break;
    }

    if (arg >= argc) {
        fprintf(stderr, "Missing object name\n");
        usage();
        exit(1);
    }
    if ((argc - arg) > SNMP_MAX_CMDLINE_OIDS) {
        fprintf(stderr, "Too many object identifiers specified. ");
        fprintf(stderr, "Only %d allowed in one request.\n",         SNMP_MAX_CMDLINE_OIDS);
        usage();
        exit(1);
    }

    /*
     * get the object names 
     */
    for (; arg < argc; arg++)
        names[current_name++] = argv[arg];

    SOCK_STARTUP;


    /*
     * Open an SNMP session.
     */
    ss = snmp_open(&session);
    if (ss == NULL) {
        /*
         * diagnose snmp_open errors with the input netsnmp_session pointer 
         */
        snmp_sess_perror("snmpget", &session);
        SOCK_CLEANUP;
        exit(1);
    }


    /*
     * Create PDU for GET request and add object names to request.
     */
    pdu = snmp_pdu_create(SNMP_MSG_GET);
    for (count = 0; count < current_name; count++) {
        name_length = MAX_OID_LEN;
        if (!snmp_parse_oid(names[count], name, &name_length)) {
            snmp_perror(names[count]);
            failures++;
        } else
            snmp_add_null_var(pdu, name, name_length);
    }
    if (failures) {
        snmp_close(ss);
        SOCK_CLEANUP;
        exit(1);
    }


    /*
     * Perform the request.
     *
     * If the Get Request fails, note the OID that caused the error,
     * "fix" the PDU (removing the error-prone OID) and retry.
     */
  retry:
    status = snmp_synch_response(ss, pdu, &response);
    if (status == STAT_SUCCESS) {
        if (response->errstat == SNMP_ERR_NOERROR) {
            for (vars = response->variables; vars;
                 vars = vars->next_variable)
                print_variable(vars->name, vars->name_length, vars);

        } else {
            fprintf(stderr, "Error in packet\nReason: %s\n",
                    snmp_errstring(response->errstat));

            if (response->errindex != 0) {
                fprintf(stderr, "Failed object: ");
                for (count = 1, vars = response->variables;
                     vars && count != response->errindex;
                     vars = vars->next_variable, count++)
                /*EMPTY*/;
                if (vars) {
                    fprint_objid(stderr, vars->name, vars->name_length);
        }
                fprintf(stderr, "\n");
            }
            exitval = 2;

            /*
             * retry if the errored variable was successfully removed 
             */
            if (!netsnmp_ds_get_boolean(NETSNMP_DS_APPLICATION_ID,
                    NETSNMP_DS_APP_DONT_FIX_PDUS)) {
                pdu = snmp_fix_pdu(response, SNMP_MSG_GET);
                snmp_free_pdu(response);
                response = NULL;
                if (pdu != NULL) {
                    goto retry;
        }
            }
        }                       /* endif -- SNMP_ERR_NOERROR */

    } else if (status == STAT_TIMEOUT) {
        fprintf(stderr, "Timeout: No Response from %s.\n",
                session.peername);
        exitval = 1;

    } else {                    /* status == STAT_ERROR */
        snmp_sess_perror("snmpget", ss);
        exitval = 1;

    }                           /* endif -- STAT_SUCCESS */


    if (response)
        snmp_free_pdu(response);
    snmp_close(ss);
    SOCK_CLEANUP;
    return exitval;

}                               /* end main() */