hello i have a question about socket

#include "unp.h"
#include <netinet/tcp.h>
#include <netinet/udp.h>
#include "error.c"
union val
{
    int i_val;
    long l_val;
    struct linger linger_val;
    struct timeval  timeval_val;
}val;
static char* sock_str_flag(union val*, int);
static char* sock_str_int(union val*, int);
static char* sock_str_linger(union val*, int);
static char* sock_str_timeval(union val*, int);
struct sock_opts
{
        const char* opt_str;
        int opt_level;
        int opt_name;
        char *(*opt_val_str)(union val*, int);
}sock_opts[] = {
                {"SO_RCVBUF", IPPROTO_TCP, SO_RCVBUF, sock_str_int},
                {"SO_SNDBUF", IPPROTO_TCP, SO_SNDBUF, sock_str_int},
                {"SO_RCVBUF", IPPROTO_UDP, SO_RCVBUF, sock_str_int},
                {"SO_SNDBUF", IPPROTO_UDP, SO_SNDBUF, sock_str_int},
                {NULL, 0, 0, NULL}
                };
int main(int argc, char** argv)
{
    int fd;
    socklen_t len;
    struct sock_opts *ptr;
    for(ptr = sock_opts; ptr->opt_str != NULL; ptr++)
    {
        if(ptr->opt_str != NULL)
            printf("the printf is %s: \n", ptr->opt_str);
        else
        printf("NULL\n");
        if(ptr->opt_val_str == NULL)
            printf("(undefined)\n");
        else
        {
            switch(ptr->opt_level)
            {
                case IPPROTO_TCP:
                    fd = socket(AF_INET, SOCK_STREAM, 0);
                    break;
                case IPPROTO_UDP:
                    fd = socket(AF_INET, SOCK_DGRAM, 0);
                    printf("udp fd is %d\n", fd);
                    break;
                default:
                    err_quit("can't create fd for level %d\n", ptr->opt_level);
            }
        }
        len = sizeof(val);
        if(getsockopt(fd, ptr->opt_level, ptr->opt_name, &amp;val, &amp;len) == -1)
        {
            err_ret("getsockopt error");
        }
        else
            printf("default = %s \n", (*ptr->opt_val_str)(&amp;val, len));
        close(fd);
    }
    exit(0);
}
static char strres[128];
static char* sock_str_int(union val* ptr, int len)
{
    if(len != sizeof(int))
        snprintf(strres, sizeof(strres), "size (%d) is not int", len);
    else
        snprintf(strres, sizeof(strres), "%d", ptr->i_val);
    return strres;
}