Thread: getnameinfo() example problem

Hi,
i have seen this thread:
getnameinfo()

and i have also tried it

so, my code is the following:

Code:

 
int main(int argc, char * argv[])
{


  struct sockaddr_in sa;
   char node[NI_MAXHOST];
   sa.sin_family = AF_INET;
  
  inet_pton(AF_INET, "8.8.178.110", &sa.sin_addr);  /* Host: www.freebsd.org ; official host name: wfe0.ysv.freebsd.org*/
 
 
  int res = getnameinfo((struct sockaddr*)&sa, sizeof(sa), node, sizeof(node), NULL, 0, NI_NUMERICSERV | NI_NUMERICHOST );
  if (res)
  {
    printf("error: %d\n", res);
    printf("%s\n", gai_strerror(res));
  }
  
  printf("node=%s\n", node);
  
  printf("error: %d\n", res);
  printf("%s\n", gai_strerror(res));
  
  return 0;
}

my compile options are the follwing:

Code:

tt: tt.c
    reset 
    #gcc -Wall -ansi -pedantic tt.c -o tt
    gcc tt.c -o tt

everything works and compiles great, but instead of the hostname i get again the IP address and i dont know why
smb is able to help me?

i thank u in advance for the help

It works.
If it can't resolve the name it defaults to the number unless you use the NI_NAMEREQD flag, which makes it an error.
The NI_NUMERICHOST flag is asking it to return the numeric host, so don't use that.

Code:

#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <netdb.h>

int main(void) {
    struct sockaddr_in sa;
    char node[NI_MAXHOST];

    memset(&sa, 0, sizeof sa);
    sa.sin_family = AF_INET;
    
    inet_pton(AF_INET, "8.8.8.8", &sa.sin_addr);
    /* google-public-dns-a.google.com */

    int res = getnameinfo((struct sockaddr*)&sa, sizeof(sa),
                          node, sizeof(node),
                          NULL, 0, NI_NAMEREQD);
    
    if (res) {
        printf("error: %d\n", res);
        printf("%s\n", gai_strerror(res));
    }
    else
        printf("node=%s\n", node);
    
    return 0;
}

Originally Posted by algorism

thank u for the answering, but why it was not able to resolve the name? is there a way to find out?

for example the following piece of code works,

Code:

int main(void)
{
    struct addrinfo *result;
    struct addrinfo *res;
    int error;


    /* resolve the domain name into a list of addresses */
    error = getaddrinfo("www.freebsd.org", NULL, NULL, &result);
    if (error != 0)
    {   
        fprintf(stderr, "error in getaddrinfo: %s\n", gai_strerror(error));
        return EXIT_FAILURE;
    }   


    /* loop over all returned results and do inverse lookup */
    for (res = result; res != NULL; res = res->ai_next)
    {   
        char hostname[NI_MAXHOST] = "";


        error = getnameinfo(res->ai_addr, res->ai_addrlen, hostname, NI_MAXHOST, NULL, 0, 0); 
        if (error != 0)
        {
            fprintf(stderr, "error in getnameinfo: %s\n", gai_strerror(error));
            continue;
        }
        if (*hostname != '\0')
            printf("hostname: %s\n", hostname);
    }   


    freeaddrinfo(result);
    return EXIT_SUCCESS;
}

but why the code getnameinfo() example problem (that is, the code from the first comment)does not work?