C++从URL解析主机IP地址

Question

在Visual C++中给定URL时,如何解析主机IP地址？

Answer 1

我不确定是否有一个特定的C++类来进行主机名查找,但你总是可以使用普通的C来做这些事情.这是我在Linux,Mac OS X和Windows上编译和运行的版本.

#include <stdio.h>

#ifdef _WIN32
#  include "winsock.h"
#else
#  include <netdb.h>
#  include <arpa/inet.h>
#endif

static void initialise(void)
{
#ifdef _WIN32
    WSADATA data;
    if (WSAStartup (MAKEWORD(1, 1), &data) != 0)
    {
        fputs ("Could not initialise Winsock.\n", stderr);
        exit (1);
    }
#endif
}

static void uninitialise (void)
{
#ifdef _WIN32
    WSACleanup ();
#endif
}

int main (int argc, char *argv[])
{
    struct hostent *he;

    if (argc == 1)
        return -1;

    initialise();

    he = gethostbyname (argv[1]);
    if (he == NULL)
    {
        switch (h_errno)
        {
            case HOST_NOT_FOUND:
                fputs ("The host was not found.\n", stderr);
                break;
            case NO_ADDRESS:
                fputs ("The name is valid but it has no address.\n", stderr);
                break;
            case NO_RECOVERY:
                fputs ("A non-recoverable name server error occurred.\n", stderr);
                break;
            case TRY_AGAIN:
                fputs ("The name server is temporarily unavailable.", stderr);
                break;
        }
    }
    else
    {
        puts (inet_ntoa (*((struct in_addr *) he->h_addr_list[0])));
    }

    uninitialise ();

    return he != NULL;
}

编译完成后,提供主机名作为参数:

$ ./a.out stackoverflow.com
69.59.196.211

Answer 2

要在Windows下使用套接字函数,您必须先调用WSAStartup,指定所需的Winsock版本(为了您的目的,1.1将正常工作).然后你可以打电话gethostbyname来获取主机的地址.当你完成后,你应该调用WSACleanup.把这一切放在一起,你得到这样的东西:

#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;
}