Geek Answers Handbook

Hostname not translated to IP address using Winsock

getaddrinfo() does not translate the hostname into an IP address and therefore does not connect() to the server. Is there something wrong with my implementation - compiles without warning?

Is this connect function call specified correctly?

 connect(client, result->ai_addr, result->ai_addrlen)

The full implementation listed below:

 #include <winsock2.h> #include <ws2tcpip.h> #include <windows.h> #include <stdio.h> #include <iostream> #pragma comment(lib, "Ws2_32.lib") using namespace std; int main ( int argc, char* argv[]) { if (argc != 3) { cerr << "Usage: " << argv[0] << " [hostname] [port number]\n"; exit(EXIT_FAILURE); } WSADATA wsaData; WORD wVersionRequested; int wError; wVersionRequested = MAKEWORD(2, 2); wError = WSAStartup(wVersionRequested, &wsaData); if (wError != 0) { cerr << "WSAStartup failed with error: " << wError << endl; exit (EXIT_FAILURE); } /* * Confirm that the WinSock DLL supports 2.2. * Note that if the DLL supports versions greater * than 2.2 in addition to 2.2, it will still return * 2.2 in wVersion since that is the version we * requested. */ if (LOBYTE(wsaData.wVersion) != 2 || HIBYTE(wsaData.wVersion) != 2) { cerr << "Could not find a usable version of Winsock.dll." << endl; WSACleanup(); exit(EXIT_FAILURE); } else { cout << "The Winsock 2.2 dll was found." << endl; } SOCKET client; if ((client = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == SOCKET_ERROR) { cerr << "Error: socket() return value == SOCKET_ERROR" << endl; WSACleanup(); exit (EXIT_FAILURE); } cout << "Created a socket." << endl; struct addrinfo *result = NULL; struct addrinfo hints; memset(&hints, 0, sizeof(hints)); hints.ai_family = AF_INET; hints.ai_socktype = SOCK_STREAM; hints.ai_protocol = IPPROTO_TCP; if ((wError = getaddrinfo( argv[1], argv[2], &hints, &result)) !=0 ) { freeaddrinfo(result); WSACleanup(); if (wError == 11001) { cerr << "Error: occurred: getaddrinfo() failed " << wError << " - Host not found." << endl; exit(EXIT_FAILURE); } cerr << "Error: occurred: getaddrinfo() failed " << wError << endl; exit(EXIT_FAILURE); } /* * Attempt to connect to the Server * */ switch (wError = connect(client, result->ai_addr, result->ai_addrlen)) { case 0: cerr << "Resolved hostname." << endl; break; case SOCKET_ERROR: wError = WSAGetLastError(); cerr << "Error: connet() failed " "Details: " << wError << endl; closesocket(client); freeaddrinfo(result); WSACleanup(); exit(EXIT_FAILURE); break; default: cerr << "Fatal connect() error: unexpected " "return value." << endl; closesocket(client); freeaddrinfo(result); WSACleanup(); exit(EXIT_FAILURE); break; } cout << "Connected to server." << endl; closesocket(client); freeaddrinfo(result); WSACleanup(); exit(EXIT_SUCCESS); }
+4
source share
2 answers

getaddrinfo may indicate an IPv6 address, or there may be more than one IP address on the computer and you are trying to connect to the wrong one.

In addition, if your server is listening on 127.0.0.1 and you are trying to connect to a real IP address, the connection will fail. Similarly, if the server is listening on a real IP address and you are trying to connect using 127.0.0.1, the connection will fail. If the server is listening on 0.0.0.0, both addresses should work.

To listen to 0.0.0.0, you will have code similar to this:

 sockaddr_in sin; sin.sin_family = AF_INET; sin.sin_addr.s_addr = INADDR_ANY; sin.sin_port=htons( port_num ); bind( s, (sockaddr *)&sin, sizeof( sin ) );
+4
source

Try setting hint.ai_family to AF_UNSPEC instead of AF_INET , I believe that when AF_INET is set, getaddrinfo functions exclude an IPv4-like address.

+1
source

More articles:


All Articles