How can I extract the domain from a URL?

I'm currently making a few changes in the rTorrent source. I have the following code:

torrent::Object
appl开发者_开发知识库y_to_domain(const torrent::Object& rawArgs) {

 const char * url = rawArgs.as_string().c_str();
 char buffer[50];
 snprintf(buffer, 50, "URL: %s.", url);

  return std::string(buffer);
}

I need to extract the domain from url. There's a regex.h included in the source but I'm not sure if I can use that or if I need to use a different regex library.

Link to regex.h

---

The only thing that "regex" implementation handles is the wildcard character, *. (BTW, I'm just assuming it's a wildcard, since it's the only character that's recognised and the comments seem to hint as much, but I haven't actually verified it.)

Use a proper regex library like Boost.Regex.

---

// This is a hacked up whole string pattern matching. Replace with
// TR1's regex when that becomes widely available. It is intended for
// small strings.

That's not going to work for extracting the domain. Use Boost or VSCRT TR1 instead.

---

See *get_active_tracker_domain* in command_pyroscope.cc

---

In windows:

#include <winsock2.h>
#include <windows.h>
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cctype>
#include <locale>
#pragma comment(lib,"ws2_32.lib")
using namespace std;

string website_HTML;
locale local;

//***************************
void get_Website(char *url );
void extract_URL();
//***************************


int main ()
{
    char *url="www.bbc.com";
    get_Website(url );
    extract_URL();

    return 0;
}



//***************************
void get_Website(char *url )
{
        WSADATA wsaData;
        SOCKET Socket;
        SOCKADDR_IN SockAddr;


        int lineCount=0;
        int rowCount=0;

        struct hostent *host;
        char *get_http= new char[256];

        memset(get_http,' ', sizeof(get_http) );
        strcpy(get_http,"GET / HTTP/1.1\r\nHost: ");
        strcat(get_http,url);
        strcat(get_http,"\r\nConnection: close\r\n\r\n");

        if (WSAStartup(MAKEWORD(2,2), &wsaData) != 0) 
        {
            cout << "WSAStartup failed.\n";
            exit(0);
        }

        Socket=socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
        host = gethostbyname(url);

        SockAddr.sin_port=htons(80);
        SockAddr.sin_family=AF_INET;
        SockAddr.sin_addr.s_addr = *((unsigned long*)host->h_addr);

        cout << "Connecting to ["<< url<<"]...\n";
        if(connect(Socket,(SOCKADDR*)(&SockAddr),sizeof(SockAddr)) != 0)
        {
            cout << "Could not connect\n";
            exit(0);
        }
        cout << "Connected. (success!)\n";
        std::cout << std::flush;
        send(Socket,get_http, strlen(get_http),0 );     
        char buffer[10000];
        int nDataLength;
        int i = 0;

        while ((nDataLength = recv(Socket,buffer,10000,0)) > 0)
        {       


            while (buffer[i] >= 32 || buffer[i] == '\n' || buffer[i] == '\r') 
            {       
                website_HTML+=buffer[i];                
                i += 1;

            }

        }
        cout<<"\n"<<i<<" bytes downloaded \n\n";
        closesocket(Socket);
        WSACleanup();
        delete[] get_http;
}


void extract_URL()
{
    for (size_t i=0; i<website_HTML.length(); ++i) website_HTML[i]= tolower(website_HTML[i],local);

    std::string to_find = "http:";
    std::vector<string> extracted_website_URL;
    std::string string_to_split;
    char chr_String[1000];
    int count = 0;
    char seps[]   = "\"";
    char *token;

    cout << "\nExtracting url..  ";
    for (int j = 0; j < website_HTML.length() - to_find.length(); j++) 
    {
        if (website_HTML.substr(j, to_find.length()) == to_find)
        {
            count++;
            string_to_split=website_HTML.substr(j, to_find.length()+256);
            strcpy(chr_String , string_to_split.c_str() );
            token = strtok( chr_String, seps );
            extracted_website_URL.push_back(token);
            //cout<<website_HTML.substr(j, to_find.length()+30)<<" \n";

        }

        std::cout << "\b\\" << std::flush;       
        std::cout << "\b|" << std::flush;        
        std::cout << "\b/" << std::flush;        
        std::cout << "\b-" << std::flush;
    }


    for(j=0;j<extracted_website_URL.size();j++) cout<<extracted_website_URL[j] <<"   \n";
    cout<<"\n"<<extracted_website_URL.size()<<" URL's extracted ";
    cout<<"\n\n";

}

---

something basic but that may do the job:

#include <regex>

std::string getHostFromUrl(const std::string & url) {
  std::regex urlRe("^.*://([^/?:]+)/?.*$");

  return std::regex_replace(url, urlRe, "$1");
}

---

Try C++11 Regex:

#include <iostream>
#include <string>
#include <regex>
 
int main()
{
    std::string str("The link of this question: https://stackoverflow.com/questions/3073753/how-can-i-extract-the-domain-from-a-url \
Other urls are https://www.google.com, facebook.com. https://my_site.online.com:1234");
    std::regex r("https?:\\/\\/(www\\.)?[-a-zA-Z0-9@:%._\\+~#=]{1,256}");
    std::smatch sm;
    while(regex_search(str, sm, r))
    {
        std::cout << sm.str() << '\n';
        str = sm.suffix();
    }
}

---

in Qt, you can use QUrl:

QString url("https://somedomain.com/index/of/somepage/blah/blah");
QUrl qu(url);
qDebug() << "qu.host " << qu.host();

it will give you : somedomain.com