Accelerated C++ 6.1查找URL

作为字符串处理的实例，编写一个查找URL的函数。

URL格式：  protocol-name://resource-name

// 查找 URL#include <iostream>#include <string>#include <vector>#include <algorithm>using namespace std;bool not_url_char(char c){ // characters, in addition to alphanumerics, that can appear in a URL static const string url_ch = "~;/?:@=&$-_.+!*'(),"; // see whether c can appear in a URL and return the negative 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; // i marks where the separator was found iter i = b; while ((i = search(i, e, sep.begin(), sep.end())) != e){ // make sure the separator isn't at the beginning or end of the line if (i != b && i + sep.size() != e) { // beg marks the beginning of the protocol-name iter beg = i; while (beg != b && isalpha(beg[-1])) --beg; // is there at least one appropriate character before and after the separator? if (beg != i && !not_url_char(i[sep.size()])) return beg; } // the separator we found wasn't part of a URL advance i past this separator 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(); // look through the entire input while (b != e) { // look for one or more letters followed by :// b = url_beg(b, e); // if we found it if (b != e) { // get the rest of the URL iter after = url_end(b, e); // remember the URL ret.push_back(string(b, after)); // advance b and check for more URLs on this line b = after; } } return ret;}int main(){ string s; while (getline(cin, s)) { vector<string> v = find_urls(s); for (vector<string>::size_type i = 0; i != v.size(); ++i) { cout << v[i] << endl; } } return 0;}