The option is unknown at the level indicated.

Does my system not support this constant?
code:

Code:

---

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <errno.h>
#include <stdlib.h>

int main()
{
int sock = socket(AF_LOCAL, SOCK_STREAM, 0);
        if(sock == -1)
          printf("Error\n");

    char *name;
        name="ccmni0";
        if( (setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, name, 6)) < 0)
          printf("SO_BINDTODEVICE error\n");
        char *arr[7];
        int ss = 7;
        ret = getsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, &arr, &ss);
        if(ret==0)
        {
                printf("SO_BINDTODEVICE: %s\n", arr);
        }
        else
        {
                if(errno==EBADF)
            printf("The argument sockfd is not a valid file descriptor.\n");
                else if(errno==EFAULT)
                    printf("The address pointed to by optval is not in a valid part of.the process address space.  For getsockopt(), this error may also be returned if optlen is not in a valid part of the process address space.\n");
                else if(errno==EINVAL)
                    printf("optlen invalid in setsockopt().  In some cases this error.can also occur for an invalid value in optval (e.g., for the IP_ADD_MEMBERSHIP option described in ip(7)).\n");
                else if(errno==ENOPROTOOPT)
                    printf("The option is unknown at the level indicated.\n");
                else if(errno==ENOTSOCK)
                    printf("The file descriptor sockfd does not refer to a socket.\n");
}

---

I write the program from the phone and therefore my internet interface is called ccmni0. Why can not I access the variable A and write the value there with the setsockopt command can I? This example is working and taken from the documentation, you can check at yourself, there is nothing to correct it.

Quote:

---

Originally Posted by DevZero

This example is working and taken from the documentation, you can check at yourself, there is nothing to correct it.

---

Please stop helping this mindless retard.

Quote:

---

Originally Posted by algorism

Please stop helping this mindless retard.

---

Where did you get rid of retard? Better help and explain it in clear language to me and explain to me why the manuals are written in such an incomprehensible language that no one can understand

The first question is why aren't you just using bind()?

Next, the manual page for socket() says this

Quote:

---

SO_BINDTODEVICE
Bind this socket to a particular device like "eth0", as specified in the passed interface name. If the name is an empty string or the option length is zero, the socket device binding is removed. The passed option is a variable-length null-terminated interface name string with the maximum size of IFNAMSIZ. If a socket is bound to an interface, only packets received from that particular interface are processed by the socket. Note that this only works for some socket types, particularly AF_INET sockets. It is not supported for packet sockets (use normal bind(2) there).

---

Which then begs the question as to where you got your example using AF_LOCAL ?

Even the tiniest amount of effort on your part would have found a lot of further reading material on the subject.
c - bind vs SO_BINDTODEVICE socket - Stack Overflow
c - Problems with SO_BINDTODEVICE Linux socket option - Stack Overflow
c++ - When should I call the SO_BINDTODEVICE socket option for a STREAM socket - Stack Overflow

In particular, you might need (as I did when I tried it), to have 'root' privilege when trying to do setsockopt.

Lastly, what's all this?

Code:

---

    char *arr[7];
    int ss = 7;

---

This is nothing like what getsockopt requires.

Code:

---

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <net/if.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>

int main()
{
  int sock = socket(AF_INET, SOCK_STREAM, 0); //!! not AF_LOCAL
  if (sock == -1)
    perror("socket()");

  char *name;
  name = "eth0";
  if ((setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, name, strlen(name))) < 0)
    perror("setsockopt(SO_BINDTODEVICE)");
  char arr[IFNAMSIZ] = { 0 };
  int ss = IFNAMSIZ;
  int ret = getsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, arr, &ss);
  if (ret == 0) {
    printf("SO_BINDTODEVICE: %s\n", arr);
  } else {
    perror("getsockopt(SO_BINDTODEVICE)");
  }
}

$ ./a.out
setsockopt(SO_BINDTODEVICE): Operation not permitted
SO_BINDTODEVICE:

$ sudo ./a.out
SO_BINDTODEVICE: eth0

---