Strange problem encountered when getting Sohu host with gethostbyaddr

baximayi

Main program

void GetHostInfoByAddr (const char * addr)
{
hostent * phost = NULL;
unsigned long u_ip = inet_addr (addr);
phost = gethostbyaddr ((char *)&u_ip, 4, AF_INET);
cout << WSAGetLastError () << endl;
if (phost == NULL)
{
cerr << "get host info failed ----" << GetLastError () << endl;
return;
}
cout << phost-> h_name << endl; // Error
return;
}


int main ()
{
WSADATA wsadata;
WSAStartup (MAKEWORD (2,2),&wsadata);
    //GetHostInfoByAddr("202.102.14.141 ");
GetHostInfoByAddr ("218.30.66.201"); // Sohu IP, PING get
WSACleanup ();
system ("pause");
return 0;
}

WSAGetLastError () returns a value of 0 and phost is not empty, indicating that the function call was successful.
However, when outputting the host name, it reports "0xffff305c" memory referenced by the instruction "0x00421940. This memory cannot be" read ".
That is why ah?
If gethostbyaddr can only get the hostname of the LAN, but I can get the host correctly using 202.102.14.141, please verify my code, thank you.

baximayi

The Ping Sohu IP should be 221.236.12.205 or 221.236.12.214.

wygost

Please refer to the MSDN documentation. The return value of WSAGetLastError() is 0, which does not mean that the requested address must have a corresponding host name. If WSAGetLastError() == 11001, it means that there is no host name, so there is an access violation.

Please see msdn example code:


//----------------------
// Declare and initialize variables
hostent* remoteHost;
char* host_name;
unsigned int addr;

//----------------------
// User inputs name of host
printf("Input name of host: ");
host_name = (char*) malloc(sizeof(char*)*16);
fgets(host_name, 16, stdin);

// If the user input is an alpha name for the host, use gethostbyname()
// If not, get host by addr (assume IPv4)
if (isalpha(host_name[0])) {/* host address is a name */
  host_name[strlen(host_name)-1] = '\0'; /* NULL TERMINATED */
  remoteHost = gethostbyname(host_name);
}
else {
  addr = inet_addr(host_name);
  remoteHost = gethostbyaddr((char *)&addr, 4, AF_INET);
}

if (WSAGetLastError() != 0) {
  if (WSAGetLastError() == 11001)
  printf("Host not found...\nExiting.\n");
}
else
  printf("error#:%ld\n", WSAGetLastError());

// The remoteHost structure can now be used to
// access information about the host

baximayi

3Ks