getaddrinfo()与IPv6没有意义

Question

我不明白为什么getaddrinfo不返回有效的IPv6地址.

在我的系统上,下面的代码是打印22:B8:00:00:00:00:00:00:00:00:00:00:00:00,但我期望在01某个地方,因为localhost应该解决::1.

同时,sa_data只有14个字节,而IPv6地址是16个字节,所以似乎最后几个字节总是被切断,并且该函数不能返回IPv6地址？

有人可以解释发生了什么吗？我该如何在IPv6中使用此功能？

#include <stdio.h>
#include <WinSock2.h>
#include <WS2TCPIP.h>
#pragma comment(lib, "WS2_32")

int main(int argc, char *argv[])
{
    WSADATA wsadata;
    WSAStartup(0x0002, &wsadata);
    addrinfo addr_hints = { 0, PF_INET6, SOCK_DGRAM, IPPROTO_UDP }, *addrs_out;
    getaddrinfo("localhost", "8888", &addr_hints, &addrs_out);
    fprintf(stderr,
        "%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X\n",
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 0]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 1]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 2]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 3]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 4]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 5]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 6]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 7]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 8]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[ 9]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[10]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[11]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[12]),
        static_cast<unsigned char>(addrs_out->ai_addr->sa_data[13]));
    freeaddrinfo(addrs_out);
    return 0;
}

Answer 1

sockaddr 结构定义供参考:

struct sockaddr {
    ushort  sa_family;
    char    sa_data[14];
};


struct sockaddr_in6 {
    short   sin6_family;
    u_short sin6_port;
    u_long  sin6_flowinfo;
    struct  in6_addr sin6_addr;
    u_long  sin6_scope_id;
};

当ai_family == AF_INET6 ai_addr实际指向一个struct sockaddr_in6.您要打印的前几个字节是sin6_port和sin6_flowinfo.IPv6地址之后.

编辑添加:

您可以使用ai_addr具有类似功能直接bind()和getnameinfo().您通常不需要深入了解结构定义细节.例如,我会用getnameinfo()与NI_NUMERICHOST获得打印地址.