sin6_addr打印:string to sockaddr_in6 and sockaddr_in6 to string

函式原型：
#include <arpa/inet.h>
const char *inet_ntop(int af, const void *src, char *dst, socklen_t size);   //"network to printable"

int inet_pton(int af, const char *src, void *dst);

一个使用例子：
char str[INET6_ADDRSTRLEN];
if(inet_ntop(AF_INET6, &sin6_addr, str, INET6_ADDRSTRLEN) == NULL){
    perror("inet ntop/n");
    printf("error\n");
}
syslog(LOG_ERR, "sin6_addr=%s\n", str);
printf("sin6_addr=%s\n", str);        

推荐阅读：

Beej's Guide to Network Programming
English:
https://beej.us/guide/bgnet/html/multi/inet_ntopman.html
繁体中文，目录清晰：
http://beej-zhtw.netdpi.net/09-man-manual/9-14-inet_ntop-inet_pton

// IPv6 demo of inet_ntop() and inet_pton()
// (basically the same except with a bunch of 6s thrown around)

struct sockaddr_in6 sa;
char str[INET6_ADDRSTRLEN];

// store this IP address in sa:
inet_pton(AF_INET6, "2001:db8:8714:3a90::12", &(sa.sin6_addr));

// now get it back and print it
inet_ntop(AF_INET6, &(sa.sin6_addr), str, INET6_ADDRSTRLEN);

printf("%s\n", str); // prints "2001:db8:8714:3a90::12"

// Helper function you can use:

//Convert a struct sockaddr address to a string, IPv4 and IPv6:

char *get_ip_str(const struct sockaddr *sa, char *s, size_t maxlen)
{
    switch(sa->sa_family) {
        case AF_INET:
            inet_ntop(AF_INET, &(((struct sockaddr_in *)sa)->sin_addr),
                    s, maxlen);
            break;

        case AF_INET6:
            inet_ntop(AF_INET6, &(((struct sockaddr_in6 *)sa)->sin6_addr),
                    s, maxlen);
            break;

        default:
            strncpy(s, "Unknown AF", maxlen);
            return NULL;
    }

    return s;
}

参考：

网络编程中常见地址结构与转换（IPv4/IPv6)
https://www.cnblogs.com/sunada2005/archive/2013/08/06/3240724.html
Linux网络编程IPv4和IPv6的inet_addr、inet_aton、inet_pton等函数小结
https://blog.csdn.net/ithomer/article/details/6100734

一个例子很清晰：
https://gist.github.com/q2hide/244bf94d3b72cc17d9ca