C++中的客户端,使用gethostbyname或getaddrinfo

1> Remy Lebeau..：

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这些gethostbyname()和gethostbyaddr()函数在大多数平台上都已弃用,并且它们不实现对IPv6的支持.IPv4已达到极限,现在世界已经转向IPv6一段时间了.分别使用getaddrinfo()和getnameinfo()代替.

回答你的问题:

A. getaddrinfo()并且getnameinfo()可用于客户端和服务器一样,就像gethostbyname()和gethostbyaddr()即可.它们只是主机/地址解析功能,如何使用已解析的值取决于调用应用程序来决定.

B.客户端代码使用getaddrinfo()看起来像这样:

int OpenConnection(const char *hostname, int port)
{
    int sd, err;
    struct addrinfo hints = {}, *addrs;
    char port_str[16] = {};

    hints.ai_family = AF_INET; // Since your original code was using sockaddr_in and
                               // PF_INET, I'm using AF_INET here to match.  Use
                               // AF_UNSPEC instead if you want to allow getaddrinfo()
                               // to find both IPv4 and IPv6 addresses for the hostname.
                               // Just make sure the rest of your code is equally family-
                               // agnostic when dealing with the IP addresses associated
                               // with this connection. For instance, make sure any uses
                               // of sockaddr_in are changed to sockaddr_storage,
                               // and pay attention to its ss_family field, etc...
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    sprintf(port_str, "%d", port);

    err = getaddrinfo(hostname, port_str, &hints, &addrs);
    if (err != 0)
    {
        fprintf(stderr, "%s: %s\n", hostname, gai_strerror(err));
        abort();
    }

    for(struct addrinfo *addr = addrs; addr != NULL; addr = addr->ai_next)
    {
        sd = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
        if (sd == -1)
        {
            err = errno;
            break; // if using AF_UNSPEC above instead of AF_INET/6 specifically,
                   // replace this 'break' with 'continue' instead, as the 'ai_family'
                   // may be different on the next iteration...
        }

        if (connect(sd, addr->ai_addr, addr->ai_addrlen) == 0)
            break;

        err = errno;

        close(sd);
        sd = -1;
    }

    freeaddrinfo(addrs);

    if (sd == -1)
    {
        fprintf(stderr, "%s: %s\n", hostname, strerror(err));
        abort();
    }

    return sd;
}

2> paulsm4..：

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我总是使用gethostbyname(),因为"永远".它始终有效,它继续工作,而且"更简单".

getaddrinfo()是更新的函数:

http://man7.org/linux/man-pages/man3/getaddrinfo.3.html

getaddrinfo()函数将gethostbyname(3)和getservbyname(3)函数提供的功能组合到一个接口中,但与后面的函数不同,getaddrinfo()是可重入的,并允许程序消除IPv4与IPv6的依赖关系.

我知道getaddrinfo()更强大,更高效,更安全:你不应该使用gethostbyname()

附录:

在回答您的具体问题时:

A] getaddrinfo()优先gethostbyname()于查找主机名的IP地址; "客户"或"服务器".

B]问:我如何修改提示结构和函数参数？

答:"提示"看起来不错,但我可能会将端口修改为NULL.

这是一个完整的例子:

https://www.kutukupret.com/2009/09/28/gethostbyname-vs-getaddrinfo/

#include 
#include 
#include 
#include 
#include 
#include 

int main(int argc, char *argv[])
{
    struct addrinfo hints, *res, *p;
    int status;
    char ipstr[INET6_ADDRSTRLEN];

    if (argc != 2) {
       fprintf(stderr, "Usage: %s hostname\n", argv[0]);
       return 1;
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC; // AF_INET or AF_INET6 to force version
    hints.ai_socktype = SOCK_STREAM;

    if ((status = getaddrinfo(argv[1], NULL, &hints, &res)) != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(status));
        return 2;
    }

    for(p = res;p != NULL; p = p->ai_next) {
        void *addr;
        if (p->ai_family == AF_INET) {
            return 1;  
        } else {
            struct sockaddr_in6 *ipv6 = (struct sockaddr_in6 *)p->ai_addr;
            addr = &(ipv6->sin6_addr);

            /* convert the IP to a string and print it: */
            inet_ntop(p->ai_family, addr, ipstr, sizeof ipstr);             
            printf("Hostname: %s\n", argv[1]);
            printf("IP Address: %s\n", ipstr);
        }
    }

    freeaddrinfo(res); // free the linked list     
    return 0;
}

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@jiveturkey`getservbyname()`只是将符号"服务名称"(如`http`或`ftp`)映射到端口号的函数,它与您运行的是客户端还是服务器无关.它可能只是这样命名,因为在Unix系统上它读取`/ etc/services`来指定映射.

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不,我想传达的印象就是`getaddrinfo()`是将主机名映射到IP的"更好"方式,而不是经典的`gethostbyname()`.这两个功能都适用于*EITHER*客户端或服务器.