Could not make getnameinfo working on my UDP code - c++

Question

I have the following UDP client communication code:
clUDPPort::clUDPPort(int prt,string hostname){ //client
nServerPort = prt;
szHostName = hostname;
nSocketId = socket (AF_INET , SOCK_DGRAM, 0 ) ;
serverAddr.sin_family = AF_INET;
serverAddr.sin_port = htons(nServerPort) ;
host = gethostbyname(szHostName.c_str()) ;
memcpy( (char*)&serverAddr.sin_addr,(char*) host->h_addr , host->h_length ) ;
//nSize = sizeof(serverAddr);
}
This code is part of a CGI application that is installed on an embedded linux device. When testing on my PC, the host name is passed as local address like 192.168.2.50, when deployed to the device the host name is 127.0.0.1 because there is a service program that my application connects with.
The problem is a linking warning saying:
/home/abdalla/XML_Communication/udpport.cpp:24: warning: gethostbyname is obsolescent, use getnameinfo() instead.
This is generated by KDevelop 4.7 on openSUSE 13.2 64-bit. I tried to use getnameinfo but could not figure out how to make it work because according to the documentation it asks for host name and server name. Apparently in my code the host and the server are the same. Can you help me making getnameinfo working for my code ? Thanks.

Answer 1

What you actually need to translate a name into address is probably getaddrinfo. See the linux man page for details which include sample code.

Answer 2

Here is my code which is using getaddrinfo().
///the common socket address. we will use this structure to describe all Internet address.
struct nw_sockaddr_t
{
struct sockaddr addr; //currently 16 bytes
unsigned int addrlen;
};
bool nw_sock_addr_fill(nw_sockaddr_t& addr, const char* node, const char* service)
{
struct addrinfo hints;
memset(&hints, 0, sizeof(hints));
hints.ai_family = addr.addr.sa_family;
hints.ai_socktype = SOCK_STREAM;
struct addrinfo* ai = NULL, *ai_o = NULL;
bool good = false;
do
{
if(0!=getaddrinfo(node, service, &hints, &ai))
break;
ai_o = ai;
if(NULL!=ai)
{
if(NULL==ai->ai_next)
{
memcpy(&addr.addr, ai->ai_addr, sizeof(addr.addr));
addr.addrlen = ai->ai_addrlen;
good = true;
}
else
{
while(NULL!=ai->ai_next)
{
if(ai->ai_family==AF_INET || ai->ai_family==AF_INET6)
break;
ai = ai->ai_next;
}
if(NULL!=ai)
ai = ai_o;
memcpy(&addr.addr, ai->ai_addr, sizeof(addr.addr));
addr.addrlen = ai->ai_addrlen;
good = true;
}
}
}while(false);
if(NULL!=ai_o)
freeaddrinfo(ai_o);
if(good)
{
if(AF_INET==addr.addr.sa_family)
{
struct sockaddr_in* in = (sockaddr_in*)(&addr.addr);
if(0==in->sin_port)
in->sin_port = htons(ut_n2u32(service, strlen(service)));
}
else if(AF_INET6==addr.addr.sa_family)
{
struct sockaddr_in6* in = (sockaddr_in6*)(&addr.addr);
if(0==in->sin6_port)
in->sin6_port = htons(ut_n2u32(service, strlen(service)));
}
}
return good;
}
Usage:
nw_sockaddr_t addr;
if(nw_sock_addr_fill(addr, "127.0.0.1", "80"))
{
//here you will get the ipv4 address
struct sockaddr_in* addr_in = (struct sockaddr_in*)(&addr.addr);
}