How to get local IP

[zlatko]

I use next way and it work correct always for me

char hostname[255];
int lhnr_res = gethostname(hostname, 255); 
 
if(lhnr_res)
  printf("Can't resolve hostname!\n");
else		
  printf("Host name is '%s'\n", hostname);
 
hostent *lh= gethostbyname(hostname); 
 
if(!lh)
  printf("Can't resolve ipaddress!\n");
else
{
  QStringList ipList;
  for(int i=0; ;i++)
  {
    char *ipadr=lh->h_addr_list[i];
 
    if(ipadr)
    {
      QString sIP;
      sIP.sprintf("%d.%d.%d.%d", (unsigned char)ipadr[0], (unsigned char)ipadr[1], (unsigned char)ipadr[2], (unsigned char)ipadr[3]);
      ipList.append(sIP);
      printf("IP addres is %s:\n", sIP.data());
    }
    else
      break;
   }
}

char hostname[255];
int lhnr_res = gethostname(hostname, 255); 

if(lhnr_res)
  printf("Can't resolve hostname!\n");
else		
  printf("Host name is '%s'\n", hostname);
	
hostent *lh= gethostbyname(hostname); 

if(!lh)
  printf("Can't resolve ipaddress!\n");
else
{
  QStringList ipList;
  for(int i=0; ;i++)
  {
    char *ipadr=lh->h_addr_list[i];

    if(ipadr)
    {
      QString sIP;
      sIP.sprintf("%d.%d.%d.%d", (unsigned char)ipadr[0], (unsigned char)ipadr[1], (unsigned char)ipadr[2], (unsigned char)ipadr[3]);
      ipList.append(sIP);
      printf("IP addres is %s:\n", sIP.data());
    }
    else
      break;
   }
}

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[wysota]

Probably because you have the hostname set correctly. It doesn't work for me at all.

[naresh]

well the only way i found to do this... is connecting with QTcpSocket somwhere (ie. google at port 80). After that localAddress return my IP address...

[zlatko]

Probably because you have the hostname set correctly. It doesn't work for me at all.

I'm not strong in network admining but explain me at what situation and why can be declare failed hostname...
You explain it in upper posts but my poor english cant give me correct answer

[wysota]

You rely on a gethostbyname() call. When you pass it a host name and not an address, a lookup is made and correct IP is returned. Now if it's not possible to determine an IP for a particular host, the function will fail.

Suprisingly, it doesn't even work for me if I pass "localhost" as the hostname, which should always be resolvable. Maybe there is something wrong with your code. sIP.data() simply returns an empty string for me.

[zlatko]

No it copy/paste code for one our program that correct cat local IP on Windows XP, Linux Suse, and today begin work under FreeBSD...
Used Qt3..