Get IP-address by URL | 易学教程

问题

This works

target.sin_addr.s_addr = inet_addr("127.0.0.1");

but I want to put the IP from a website URL

I have tried

const char host[] = "http://www.google.com/";
struct hostent *host_ip;
host_ip = gethostbyaddr(host, strlen(host), 0);

I of corse did WSAStartup before I used gethostbyaddr();

I've tried this

target.sin_addr.s_addr = inet_addr(host_ip);

I've tried a few simmilar ones too but it isn't working. Could someone show me how to do this correctly.

Thank you!

EDIT:

When I do

host_ip = gethostbyaddr((char *)&host, strlen(host), 0);
std::cout << host_ip->h_addr;

It gives me

httpa104-116-116-112.deploy.static.akamaitechnologies.com

回答1:

inet_addr() accepts an IPv4 address string as input and returns the binary representation of that address. That is not what you want in this situation, since you don't have a IP address, you have a hostname instead.

You are on the right track by using gethostby...(), but you need to use gethostbyname() (lookup by hostname) instead of gethostbyaddr() (lookup by IP address) ¹. And you cannot pass a full URL to either of them. gethostbyname() takes only a hostname as input, so you need to parse the URL and extract its hostname, and then you can do something like this:

const char host[] = ...; // an IP address or a hostname, like "www.google.com" by itself
target.sin_addr.s_addr = inet_addr(host);
if (target.sin_addr.s_addr == INADDR_NONE)
{
    struct hostent *phost = gethostbyname(host);
    if ((phost) && (phost->h_addrtype == AF_INET))
        target.sin_addr = *(in_addr*)(phost->h_addr);
    ...
}
else
    ...

¹ BTW, the gethostby...() functions are deprecated, use getaddrinfo() and getnameinfo() instead.

const char host[] = ...; // an IP address or a hostname, like "www.google.com" by itself

addrinfo hints = {0};
hints.ai_flags = AI_NUMERICHOST;
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_protocol = IPPROTO_TCP;

addrinfo *addr = NULL;

int ret = getaddrinfo(host, NULL, &hints, &addr);
if (ret == EAI_NONAME) // not an IP, retry as a hostname
{
    hints.ai_flags = 0;
    ret = getaddrinfo(host, NULL, &hints, &addr);
}
if (ret == 0)
{
    target = *(sockaddr_in*)(addr->ai_addr);
    freeaddrinfo(addr);
    ...
}
else
    ...

回答2:

Try using getaddrinfo. There's a quick guide to using it here: http://beej.us/guide/bgnet/output/html/multipage/getaddrinfoman.html

来源：https://stackoverflow.com/questions/32639539/get-ip-address-by-url

标签

sockets

tcp

network-programming