The following examples illustrate the sysctl() call.

This example uses the sysctl() call to get the protocol driver version.

#include <stdio.h>
#include <types.h>
#include <netinet\in.h>
#include <sys\socket.h>
#include <netinet\ip_var.h>
#include <sys\sysctl.h>

int main(void)
{
        int mib[4],i;
        unsigned int  oldenp=0, newlen=0;
        struct inetvers_ctl  uap_old, *uap_new;

        mib[0]= CTL_KERN;        /* cmd             */
        mib[1]= KERN_HOSTID;     /* Protocol Family.*/
        mib[2]= IPPROTO_IP;      /* Protocol        */
        mib[3]= KERNCTL_INETVER; /* Control command for sysctl */


        uap_new = NULL;
        oldenp  = sizeof(struct inetvers_ctl);

        if (sysctl(mib,4,(void *)&uap_old,&oldenp,(void *)uap_new,newlen) > 0)
           printf ("   SOCKETS.SYS: %s\n",uap_old.versionstr);

} 

The next example shows an inetcfg sysctl() call that uses a fifth mib argument to specify the actual inet config command. This example sets then gets the value.

#include <stdio.h>
#include <types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp_var.h>
#include <sys/sysctl.h>
void  main(void)
{
        int mib[5];
        unsigned int  oldenp=0, newlen;
        struct inetcfg_ctl uap_old, uap_new;

        mib[0]= CTL_NET;         /* Top level idetifier */
        mib[1]= PF_INET;         /* Protocol Family */
        mib[2]= IPPROTO_TCP;     /* Protocol */
        mib[3]= TCPCTL_INETCFG;  /* Control command for tcp_sysctl */
        mib[4]= TCPCTL_KEEPCNT;  /* Particular Inetcfg cmd for sysctl_inetcfg */

        /* Set the Value in stack */
        uap_new.var_cur_val = 4;  /* Send 4 Keepalive probes, rather than 8 */
        newlen  = sizeof(struct inetcfg_ctl);
        if (sysctl(mib,5,(void *)NULL, &oldenp, (void *)&uap_new, newlen) < 0)
            printf("sysctl failed for requested parameter\n");

        /* Get the Value from stack */
        oldenp  = sizeof(struct inetcfg_ctl);
        if (sysctl(mib,5,(void *)&uap_old, &oldenp, (void *)NULL, 0) < 0)
            printf("sysctl failed for requested parameter\n");
        else
            printf("Current stack parameter value is %d\n",uap_old.var_cur_val);
} 

This example illustrates a sysctl() call that uses the route mib.

#include <stdio.h>
#include <string.h>
#include <types.h>
#include <netinet\in.h>
#include <sys\socket.h>
#include <netinet\ip_var.h>
#include <sys\sysctl.h>
#include <net\route.h>
#include <net\if.h>

void main(void)
{
        size_t   needed;
        int      mib[6];
        char     *buf, *next, *lim;
        struct   rt_msghdr *rtm;

        mib[0] = CTL_NET;
        mib[1] = PF_ROUTE;
        mib[2] = 0;            /* Wildcard Protocol */
        mib[3] = 0;            /* Wildcard Address Family */
        mib[4] = NET_RT_IFLIST;
        mib[5] = 0;            /* All interfaces */

        if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
                 psock_errno("route-sysctl-estimate");

        if (needed == 0) {
            printf("no routes defined\n");
            return 0;
        }

        buf = malloc(needed);
        if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0)
                psock_errno("sysctl if table");
        lim  = buf + needed;
        for (next = buf; next < lim; next += rtm->rtm_msglen) {
           rtm = (struct rt_msghdr *)next;
           switch(rtm->rtm_type){
              case RTM_IFINFO:
                { struct if_msghdr *ifm = (struct if_msghdr *) rtm;
                  printf("if#  %d ,flags 0x%x\n",ifm->ifm_index,ifm->ifm_flags);
                }
                  break;
              case RTM_NEWADDR:
                  /* Add code for this and for RTM_DELADDR etc.....*/
                  break;
           } /* switch */
        } /* for */
}