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

Question

I need to parse a url to get the protocol host path and query in an application I am writing in c++. The application is intended to be cross platform. Im surprised I cant find anything that does this in boost or poco libraries. Is it somewhere obvious Im not looking? Any suggestions on appropriate open source libs? Or is this something I just have to do my self? Its not super complicated but it seems such a common task I am surprised there isnt a common solution.

Answer 1

While I don't think there's going to be an explicit library for this, the URL syntax is pretty easy to parse.

typedef std::string::const_iterator iterator_t;
std::string someQuery(
"http://SomeHost.Somewhere.com/Path/To/File.php?query=hello");
//The first ? is the start of the query
iterator_t queryStart = std::find(someQuery.begin(), someQuery.end(), '?');
iterator_t pathEnd = queryStart; //We'll need this later
//Skip past the ? itself (if there is one)
if (queryStart != someQuery.end()) queryStart++;
std::string queryString(queryStart, someQuery.end()); //Done.

iterator_t pathStart = someQuery.begin();
//Skip past the two slashes in the protocol, to the slash just before the path
for(size_t idx = 0; pathStart != pathEnd && idx < 3; idx++) {
    pathStart = std::find(pathStart, pathEnd, L'/');
    if (pathStart != pathEnd) pathStart++;
}
std::string pathString(pathStart, pathEnd); //Done.

Answer 2

QT has QUrl for this. GNOME has SoupURI in libsoup, which you'll probably find a little more light-weight.

Answer 3

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() << ...

Answer 4

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.