Easy way to parse a url in C++ cross platform?

There is a library that's proposed for Boost inclusion and allows you to parse HTTP URI's easily. It uses Boost.Spirit and is also released under the Boost Software License. The library is cpp-netlib which you can find the documentation for at http://cpp-netlib.github.com/ -- you can download the latest release from http://github.com/cpp-netlib/cpp-netlib/downloads .

The relevant type you'll want to use is boost::network::http::uri and is documented here.

Terribly sorry, couldn't help it. :s

url.hh

#ifndef URL_HH_
#define URL_HH_    
#include <string>
struct url {
    url(const std::string& url_s); // omitted copy, ==, accessors, ...
private:
    void parse(const std::string& url_s);
private:
    std::string protocol_, host_, path_, query_;
};
#endif /* URL_HH_ */

url.cc

#include "url.hh"
#include <string>
#include <algorithm>
#include <cctype>
#include <functional>
using namespace std;

// ctors, copy, equality, ...

void url::parse(const string& url_s)
{
    const string prot_end("://");
    string::const_iterator prot_i = search(url_s.begin(), url_s.end(),
                                           prot_end.begin(), prot_end.end());
    protocol_.reserve(distance(url_s.begin(), prot_i));
    transform(url_s.begin(), prot_i,
              back_inserter(protocol_),
              ptr_fun<int,int>(tolower)); // protocol is icase
    if( prot_i == url_s.end() )
        return;
    advance(prot_i, prot_end.length());
    string::const_iterator path_i = find(prot_i, url_s.end(), '/');
    host_.reserve(distance(prot_i, path_i));
    transform(prot_i, path_i,
              back_inserter(host_),
              ptr_fun<int,int>(tolower)); // host is icase
    string::const_iterator query_i = find(path_i, url_s.end(), '?');
    path_.assign(path_i, query_i);
    if( query_i != url_s.end() )
        ++query_i;
    query_.assign(query_i, url_s.end());
}

main.cc

// ...
    url u("HTTP://stackoverflow.com/questions/2616011/parse-a.py?url=1");
    cout << u.protocol() << '\t' << u.host() << ...

Wstring version of above, added other fields I needed. Could definitely be refined, but good enough for my purposes.

#include <string>
#include <algorithm>    // find

struct Uri
{
public:
std::wstring QueryString, Path, Protocol, Host, Port;

static Uri Parse(const std::wstring &uri)
{
    Uri result;

    typedef std::wstring::const_iterator iterator_t;

    if (uri.length() == 0)
        return result;

    iterator_t uriEnd = uri.end();

    // get query start
    iterator_t queryStart = std::find(uri.begin(), uriEnd, L'?');

    // protocol
    iterator_t protocolStart = uri.begin();
    iterator_t protocolEnd = std::find(protocolStart, uriEnd, L':');            //"://");

    if (protocolEnd != uriEnd)
    {
        std::wstring prot = &*(protocolEnd);
        if ((prot.length() > 3) && (prot.substr(0, 3) == L"://"))
        {
            result.Protocol = std::wstring(protocolStart, protocolEnd);
            protocolEnd += 3;   //      ://
        }
        else
            protocolEnd = uri.begin();  // no protocol
    }
    else
        protocolEnd = uri.begin();  // no protocol

    // host
    iterator_t hostStart = protocolEnd;
    iterator_t pathStart = std::find(hostStart, uriEnd, L'/');  // get pathStart

    iterator_t hostEnd = std::find(protocolEnd, 
        (pathStart != uriEnd) ? pathStart : queryStart,
        L':');  // check for port

    result.Host = std::wstring(hostStart, hostEnd);

    // port
    if ((hostEnd != uriEnd) && ((&*(hostEnd))[0] == L':'))  // we have a port
    {
        hostEnd++;
        iterator_t portEnd = (pathStart != uriEnd) ? pathStart : queryStart;
        result.Port = std::wstring(hostEnd, portEnd);
    }

    // path
    if (pathStart != uriEnd)
        result.Path = std::wstring(pathStart, queryStart);

    // query
    if (queryStart != uriEnd)
        result.QueryString = std::wstring(queryStart, uri.end());

    return result;

}   // Parse
};  // uri

Tests/Usage

Uri u0 = Uri::Parse(L"http://localhost:80/foo.html?&q=1:2:3");
Uri u1 = Uri::Parse(L"https://localhost:80/foo.html?&q=1");
Uri u2 = Uri::Parse(L"localhost/foo");
Uri u3 = Uri::Parse(L"https://localhost/foo");
Uri u4 = Uri::Parse(L"localhost:8080");
Uri u5 = Uri::Parse(L"localhost?&foo=1");
Uri u6 = Uri::Parse(L"localhost?&foo=1:2:3");

u0.QueryString, u0.Path, u0.Protocol, u0.Host, u0.Port....

POCO's URI class can parse URLs for you. The following example is shortened version of the one in POCO URI and UUID slides:

#include "Poco/URI.h"
#include <iostream>

int main(int argc, char** argv)
{
    Poco::URI uri1("http://www.appinf.com:88/sample?example-query#frag");

    std::string scheme(uri1.getScheme()); // "http"
    std::string auth(uri1.getAuthority()); // "www.appinf.com:88"
    std::string host(uri1.getHost()); // "www.appinf.com"
    unsigned short port = uri1.getPort(); // 88
    std::string path(uri1.getPath()); // "/sample"
    std::string query(uri1.getQuery()); // "example-query"
    std::string frag(uri1.getFragment()); // "frag"
    std::string pathEtc(uri1.getPathEtc()); // "/sample?example-query#frag"

    return 0;
}