C++ IPv4与IPv6的兼容编码（转，出自http://blog.csdn.net/ligt0610/article/details/18667595）

这里不再对IPv6 socket相关编程的基础知识进行讲解，只提供一个IP协议无关的服务端和客户端的代码，仅供参考。

服务端代码：

#include <iostream>
#include <string>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <errno.h>
#include <time.h>

using namespace std;

int tcp_listen(const char *host, const char *service, const int listen_num = 5)
{
    int listenfd, ret;
    const int on = 1;
    struct addrinfo hints, *res, *ressave;
    bzero(&hints, sizeof(hints));
    hints.ai_flags = AI_PASSIVE;
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_IP;

    if (0 != (ret = getaddrinfo(host, service, &hints, &res)))
    {
        cout << "getaddrinfo error: " << gai_strerror(ret) << endl;
        return -1;
    }

    ressave = res;
    while(NULL != res)
    {
        if (-1 == (listenfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol)))
        {
            cout << "create socket error: " << strerror(errno) << endl;
            res = res->ai_next;
            continue;
        }

        if (-1 == setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)))
        {
            cout << "setsockopt error: " << strerror(errno) << endl;
            close(listenfd);
            res = res->ai_next;
            continue;
        }

        if (-1 == bind(listenfd, res->ai_addr, res->ai_addrlen))
        {
            cout << "bind error: " << strerror(errno) << endl;
                        close(listenfd);
                        res = res->ai_next;
                        continue;
        }

        if (-1 == listen(listenfd, listen_num))
        {
            cout << "listen error: " << strerror(errno) << endl;
                        close(listenfd);
                        res = res->ai_next;
                        continue;
        }

        break;
    }

    freeaddrinfo(ressave);

    if (NULL == res)
        return -1;

    return listenfd;
}

int get_addrinfo(const struct sockaddr *addr, string &ip, in_port_t &port)
{
    void *numeric_addr = NULL;
    char addr_buff[INET6_ADDRSTRLEN];

    if (AF_INET == addr->sa_family)
    {
        numeric_addr = &((struct sockaddr_in*)addr)->sin_addr;
        port = ntohs(((struct sockaddr_in*)addr)->sin_port);
    }
    else if (AF_INET6 == addr->sa_family)
    {
        numeric_addr = &((struct sockaddr_in6*)addr)->sin6_addr;
        port = ntohs(((struct sockaddr_in6*)addr)->sin6_port);
    }
    else
    {
        return -1;
    }

    if (NULL != inet_ntop(addr->sa_family, numeric_addr, addr_buff, sizeof(addr_buff)))
        ip = addr_buff;
    else
        return -1;

    return 0;
}

int main(int argc, char *argv[])
{
    int listenfd, connfd;
    struct sockaddr_storage cliaddr;
    socklen_t len = sizeof(cliaddr);
    time_t now;
    char buff[128];

    if (2 == argc) //指定端口
        listenfd = tcp_listen(NULL, argv[1]);
    else if (3 == argc) //指定本地IP和端口
        listenfd = tcp_listen(argv[1], argv[2]);
    else
    {
                cout << "usage: " << argv[0] << " [<hostname/ipaddress>] <service/port>" << endl;
        return -1;
    }

    if (listenfd < 0)
    {
        cout << "call tcp_listen error" << endl;
        return -1;
    }

    while (true)
    {
        connfd = accept(listenfd, (struct sockaddr*)&cliaddr, &len);

        string ip = "";
        in_port_t port = 0;
        get_addrinfo((struct sockaddr*)&cliaddr, ip, port);
        cout << "client " << ip << "|" << port << " login" << endl;

        now = time(NULL);
        snprintf(buff, sizeof(buff) - 1, "%.24s", ctime(&now));
        write(connfd, buff, strlen(buff));
        close(connfd);
    }

    close(listenfd);
    return 0;
}

客户端代码：

#include <iostream>
#include <string>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <errno.h>
#include <time.h>

using namespace std;

int tcp_connect(const char *host, const char *service)
{
    int sockfd, ret;
    struct addrinfo hints, *res, *ressave;
    bzero(&hints, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_IP;

    if (0 != (ret = getaddrinfo(host, service, &hints, &res)))
    {
        cout << "getaddrinfo error: " << gai_strerror(ret) << endl;
        return -1;
    }

    ressave = res;
    while (NULL != res)
    {
        if (-1 == (sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol)))
                {
                        cout << "create socket error: " << strerror(errno) << endl;
                        res = res->ai_next;
                        continue;
                }

        if (-1 == connect(sockfd, res->ai_addr, res->ai_addrlen))
        {
            cout << "connect error: " << strerror(errno) << endl;
                        close(sockfd);
            res = res->ai_next;
                        continue;
        }

        break;
    }

    freeaddrinfo(ressave);

    if (NULL == res)
        return -1;

    return sockfd;
}

int main(int argc, char *argv[])
{
    int sockfd, n;
    char buff[128];
    struct sockaddr_storage cliaddr;

    if (3 != argc)
    {
        cout << "usage: " << argv[0] << " <hostname/ipaddress> <service/port>" << endl;
        return -1;
    }

    sockfd = tcp_connect(argv[1], argv[2]);
    if (sockfd < 0)
    {
        cout << "call tcp_connect error" << endl;
        return -1;
    }

    bzero(buff, sizeof(buff));
    while ((n = read(sockfd, buff, sizeof(buff) - 1) > 0))
    {
        cout << buff << endl;
        bzero(buff, sizeof(buff));
    }
    close(sockfd);

    return 0;
}

编译：

g++ daytimesrv.cpp -o daytimesrv

g++ daytimecli.cpp -o daytimecli

运行举例:

服务端运行情况：

客户端运行情况：

以上客户端的请求与服务端的输出一一对应，客户端可以尝试用不同的IP去连接，然后观察服务端的输出，有助于理解底层的交互过程。