客户端在C++中，使用gethostbyname或getaddrinfo
客户端在C++中，使用gethostbyname或getaddrinfo
提问于 2018-10-10 02:50:50
我在C中找到了以下代码来打开一个连接：
int OpenConnection(const char *hostname, int port)
{
int sd;
struct hostent *host;
struct sockaddr_in addr = {0};
if ((host = gethostbyname(hostname)) == NULL)
{
perror(hostname);
abort();
}
sd = socket(PF_INET, SOCK_STREAM, 0);
addr.sin_family = AF_INET;
addr.sin_port = htons(port);
addr.sin_addr.s_addr = *(long *)(host->h_addr_list[0]);
if (connect(sd, (struct sockaddr *)&addr, sizeof(addr)) != 0)
{
close(sd);
perror(hostname);
abort();
}
return sd;
}当我用C++重写这段代码时，我发现我应该使用getaddrinfo而不是gethostbyname，根据这篇文章中的评论：C - What does *(long *)(host->h_addr); do?。
我查看了Beej's guide to socket programming，发现了以下示例：
int status;
struct addrinfo hints;
struct addrinfo *servinfo; // will point to the results
memset(&hints, 0, sizeof hints); // make sure the struct is empty
hints.ai_family = AF_UNSPEC; // don't care IPv4 or IPv6
hints.ai_socktype = SOCK_STREAM; // TCP stream sockets
hints.ai_flags = AI_PASSIVE; // fill in my IP for me
if ((status = getaddrinfo(NULL, "3490", &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
exit(1);
}
// servinfo now points to a linked list of 1 or more struct addrinfos
// ... do everything until you don't need servinfo anymore ....
freeaddrinfo(servinfo); // free the linked-list但是，这个示例适用于创建服务器，这让我想知道
A] getaddrinfo是否应用于客户端
和
B]我如何修改提示结构和函数参数，以使此代码适合于创建客户端？
目前，我有以下代码，但我
struct addrinfo hints = {0};
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
struct addrinfo *client_info;
const int status = getaddrinfo(hostname, port, &hints, &client_info); //don't know if its correct更新
对于任何可能觉得它有用的人来说，这是我在阅读了被接受的答案后的最终代码：
int OpenConnection(const char *hostname, const char *port)
{
struct hostent *host;
if ((host = gethostbyname(hostname)) == nullptr)
{
//More descriptive error message?
perror(hostname);
exit(EXIT_FAILURE);
}
struct addrinfo hints = {0}, *addrs;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;
const int status = getaddrinfo(hostname, port, &hints, &addrs);
if (status != 0)
{
fprintf(stderr, "%s: %s\n", hostname, gai_strerror(status));
exit(EXIT_FAILURE);
}
int sfd, err;
for (struct addrinfo *addr = addrs; addr != nullptr; addr = addr->ai_next)
{
sfd = socket(addrs->ai_family, addrs->ai_socktype, addrs->ai_protocol);
if (sfd == ERROR_STATUS)
{
err = errno;
continue;
}
if (connect(sfd, addr->ai_addr, addr->ai_addrlen) == 0)
{
break;
}
err = errno;
sfd = ERROR_STATUS;
close(sfd);
}
freeaddrinfo(addrs);
if (sfd == ERROR_STATUS)
{
fprintf(stderr, "%s: %s\n", hostname, strerror(err));
exit(EXIT_FAILURE);
}
return sfd;
}回答 1
Stack Overflow用户
回答已采纳
发布于 2018-10-10 03:38:55
gethostbyname()和gethostbyaddr()函数在大多数平台上都被弃用，并且它们不支持IPv6。IPv4已经达到了它的极限，世界已经转向IPv6一段时间了。请分别使用getaddrinfo()和getnameinfo()。
回答您的问题：
答：getaddrinfo()和getnameinfo()可以用于客户端和服务器，就像gethostbyname()和gethostbyaddr()一样。它们只是主机/地址解析函数，如何使用已解析的值由调用应用程序决定。
B.使用getaddrinfo()的客户端代码将如下所示：
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;
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/52727565
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