url_finder.cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <cctype>
#include <string>

using namespace std;

bool not_url_char(char c){
  static const string url_ch = "~;/?:@=&$-_.+!*'(),";

  return !(isalnum(c) || find(url_ch.begin(), url_ch.end(), c) != url_ch.end());
}

string::const_iterator url_end(string::const_iterator b, string::const_iterator e){
  return find_if(b, e, not_url_char);
}

string::const_iterator url_beg(string::const_iterator b, string::const_iterator e){
  static const string sep = "://";
  typedef string::const_iterator iter;

  iter i=b;
  while((i=search(i, e, sep.begin(), sep.end())) != e){

    //Make sure i was not the last char in this row.
    if(i != b && i+sep.size() != e){
      
      iter beg=i;
      //Find protocol-name previous.
      //beg[-1] equals *(beg-1)
      while(beg != b && isalpha(beg[-1]))
	beg--;

      if(beg != i && !not_url_char(i[sep.size()]))
	return beg;
    }
      i += sep.size();
    }
    return e;
}

vector<string> find_urls(const string& s){
  vector<string> ret;
  typedef string::const_iterator iter;
  iter b=s.begin(), e=s.end();

  while(b!=e){
    b=url_beg(b, e);
    if(b!=e){
      iter after = url_end(b, e);
      ret.push_back(string(b, after));
      b=after;
    }
  }
  return ret;
}