Question

How can I resolve a host IP address, given a URL in Visual C++?

Answer 1

To use the socket functions under Windows, you have to start by calling WSAStartup, specifying the version of Winsock you want (for your purposes, 1.1 will work fine). Then you can call gethostbyname to get the address of the host. When you’re done, you’re supposed to call WSACleanup. Putting that all together, you get something like this:

#include <windows.h>
#include <winsock.h>
#include <iostream>
#include <iterator>
#include <exception>
#include <algorithm>
#include <iomanip>

class use_WSA { 
    WSADATA d; 
    WORD ver;
public:
    use_WSA() : ver(MAKEWORD(1,1)) { 
        if ((WSAStartup(ver, &d)!=0) || (ver != d.wVersion))
            throw(std::runtime_error("Error starting Winsock"));
    }
    ~use_WSA() { WSACleanup(); }    
};

int main(int argc, char **argv) {
    if ( argc < 2 ) {
        std::cerr << "Usage: resolve <hostname>";
        return EXIT_FAILURE;
    }

    try { 
        use_WSA x;

        hostent *h = gethostbyname(argv[1]);
        unsigned char *addr = reinterpret_cast<unsigned char *>(h->h_addr_list[0]);
        std::copy(addr, addr+4, std::ostream_iterator<unsigned int>(std::cout, "."));
    }
    catch (std::exception const &exc) {
        std::cerr << exc.what() << "\n";
        return EXIT_FAILURE;
    }

    return 0;
}