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Stroustrup has recently posted a series of posts debunking popular myths about C++. The fifth myth is: “C++ is for large, complicated, programs only”. To debunk it, he wrote a simple C++ program downloading a web page and extracting links from it. Here it is:
#include <string>
#include <set>
#include <iostream>
#include <sstream>
#include <regex>
#include <boost/asio.hpp>
using namespace std;
set<string> get_strings(istream& is, regex pat)
{
set<string> res;
smatch m;
for (string s; getline(is, s);) // read a line
if (regex_search(s, m, pat))
res.insert(m[0]); // save match in set
return res;
}
void connect_to_file(iostream& s, const string& server, const string& file)
// open a connection to server and open an attach file to s
// skip headers
{
if (!s)
throw runtime_error{ "can't connect\n" };
// Request to read the file from the server:
s << "GET " << "http://" + server + "/" + file << " HTTP/1.0\r\n";
s << "Host: " << server << "\r\n";
s << "Accept: */*\r\n";
s << "Connection: close\r\n\r\n";
// Check that the response is OK:
string http_version;
unsigned int status_code;
s >> http_version >> status_code;
string status_message;
getline(s, status_message);
if (!s || http_version.substr(0, 5) != "HTTP/")
throw runtime_error{ "Invalid response\n" };
if (status_code != 200)
throw runtime_error{ "Response returned with status code" };
// Discard the response headers, which are terminated by a blank line:
string header;
while (getline(s, header) && header != "\r")
;
}
int main()
{
try {
string server = "www.stroustrup.com";
boost::asio::ip::tcp::iostream s{ server, "http" }; // make a connection
connect_to_file(s, server, "C++.html"); // check and open file
regex pat{ R"((http://)?www([./#\+-]\w*)+)" }; // URL
for (auto x : get_strings(s, pat)) // look for URLs
cout << x << '\n';
}
catch (std::exception& e) {
std::cout << "Exception: " << e.what() << "\n";
return 1;
}
}
Let's show Stroustrup what small and readable program actually is.
Download
http://www.stroustrup.com/C++.htmlList all links:
http://www-h.eng.cam.ac.uk/help/tpl/languages/C++.html http://www.accu.org http://www.artima.co/cppsource http://www.boost.org ...
You can use any language, but no third-party libraries are allowed.
Winner
C++ answer won by votes, but it relies on a semi-third-party library (which is disallowed by rules), and, along with another close competitor Bash, relies on a hacked together HTTP client (it won't work with HTTPS, gzip, redirects etc.). So Wolfram is a clear winner. Another solution which comes close in terms of size and readability is PowerShell (with improvement from comments), but it hasn't received much attention. Mainstream languages (Python, C#) came pretty close too.
Comment on subjectivity
The most upvoted answer (C++) at the moment votes were counted was disqualified for not following the rules listed here in the question. There's nothing subjective about it. The second most upvoted question at that moment (Wolfram) was declared winner. The third answer's (Bash) "disqualification" is subjective, but it's irrelevant as the answer didn't win by votes at any point in time. You can consider it a comment if you like. Furthermore, right now the Wolfram answer is the most upvoted answer, the accepted one, and is declared winner, which means there's zero debate or subjectivity.
Athari
Posted 2015-01-07T05:08:24.560
Reputation: 2 335
3Comments purged as they were all either obsolete or off-topic. – Doorknob – 2015-01-08T12:43:12.293
1Clarification: Shall the list of links be as incomplete as Stroustrup's one, i.e. skip any non-http-links that don't include
www(including the https, ftp, local and anchor ones on that very site) and report false-positives, i.e. non-linked mentions ofhttp://as well (not here, but in general)? – Tobias Kienzler – 2015-01-08T14:34:12.323Why is pointing out that ALL of the posted answers don't apply to what the OP asked, obsolete or off-topic? – Dunk – 2015-01-08T15:32:21.973
43To each his own, I've been called worse. If the OP's goal wasn't to try and somehow prove that Stroustrup is wrong, then I'd agree with your assessment. But the entire premise of the question is to show how "your favorite language" can do the same thing as this 50 lines of C++ in much less lines of code. The problem is that none of the examples do the same thing. In particular, none of the answers perform any error checking, none of the answers provide reusable functions, most of the answers don't provide a complete program. The Stroustrup example provides all of that. – Dunk – 2015-01-08T15:40:09.407
19What's sad is his web page isn't even valid UTF-8. Now I've gotta work around that, despite his server advertising
Content-Type: text/html; charset=UTF-8... I'm gonna email him. – Cornstalks – 2015-01-08T16:33:30.830I wish I'd thought of coming here and asking this question when I read that piece. Certainly C++ is better than it was in the past, but it's by no means optimal. – Mark Ransom – 2015-01-08T17:53:11.753
27@Dunk The other examples don't provide reusable functions because they accomplish the entire functionality of those functions in a single line and it makes no sense to make that a whole function on its own, and the C++ example doesn't perform any error checking that isn't handled natively in almost an identical manner, and the phrase "complete program" is almost meaningless. – Jason – 2015-01-08T21:09:56.453
16"You can use any language, but no third-party libraries are allowed." I don't think that's a fair requirement considering
boost/asiois used up there which is a third-party library. I mean how will languages that don't include url/tcp fetching as part of its standard library compete? – greatwolf – 2015-01-09T06:43:10.313@greatwolf They don't. That's the point. – Athari – 2015-01-09T12:21:08.510
1@Jason - upvote for "C++ example doesn't perform any error checking that isn't handled natively in almost an identical manner". – None – 2015-01-09T15:13:13.257
1
Virtually all the answers fail the task (including the original lol) because they don't pick up relative links! I did mine herE: http://forum.dlang.org/thread/tqegmjcofcnwapqitrdo@forum.dlang.org#post-nxcpwmyjfbfbjxqtmrzd:40forum.dlang.org
– Adam D. Ruppe – 2015-01-09T17:19:03.1504Is nobody gonna talk about using regexes to parse HTML? Really? I mean Stroustrup does it himself but at least his regex doesn't rely on the HTML-attribute using
"and only ever"to delimit its value. 9 out of 10 answers here would fail on<a href='http://htmlparsing.com/regexes.html'>– asontu – 2015-01-12T12:44:03.563@funkwurm Problems with the provided solutions have been mentioned many times, you just need to look through comments. The famous "parsing HTML with regex" answer from SO has been brought up too. Many comments have been removed by the mod though. – Athari – 2015-01-12T19:59:37.993
@undergroundmonorail BF++ does. It is giving me strange and deviant thoughts. – ymbirtt – 2015-01-14T16:29:33.650
2I have to admit, I'm surprised by Stroustrup's claim that most people believe that C++ is used for large programs. I (probably incorrectly) believe the opposite - that for large programs, it's worthwhile to use a language like Java or C# that makes it harder to shoot yourself in the foot! – Kevin – 2015-01-15T00:22:42.010
12
He's... parsing... html... with... regex... twitch
– Riot – 2015-01-15T05:53:35.8271Its a little odd to me that Stroustrup's challenge is to write C++ code that imports no third party code and the first line (or so, I'm not going to page back and lose my post thus far) is an import of boost's asio library. It kind of makes OP's opinion suspect. But in any case, comparing different languages in this task is very much like comparing apples and oranges. It doesn't really make much sense to use a hammer to tap in a pin, but it can be done; it doesn't make much sense to write assembly code to extract url's from a web page but it can be done. I suspect you could write a RoR program – None – 2015-01-15T04:07:04.293
2
This code snippet appears in a hacking scene on the Netflix series "Limitless"; Season 1, Episode 10, ~13:05. Proof: http://i.imgur.com/7a16H8y.png
– Dan – 2017-02-03T02:15:16.490I'm casting a close vote as lacking an objective winning criterion because the question is tagged [tag:popularity-contest], but the "winner" paragraph at the end suggests the OP is subjectively disqualifying answers. – pppery – 2020-12-26T03:32:53.383
1@pppery I really wonder what are you trying to achieve by closing this question. – the default. – 2020-12-26T07:06:11.653
2@pppery The most upvoted answer (C++) at the moment votes were counted was disqualified for not following the rules listed in question. There's nothing subjective about it. The second most upvoted question at that moment (Wolfram) was declared winner. The third answer's (Bash) "disqualification" is subjective, but it's irrelevant as the answer didn't win by votes at any point in time. You can consider it a comment if you like. Furthermore, right now the Wolfram answer is the most upvoted answer, the accepted one, and is declared winner, which means there's zero debate or subjectivity. – Athari – 2020-12-26T13:01:21.733
@pppery Does that mean that if the OP edited out the “Winner” section and just left the answer accepted without any comments the question would have an objective winning criteria? I agree with the OP here, pop-con is objective, and “no third party libraries”, while not a great thing to ban, still disqualifies the C++ answer, making the Wolfram answer the clear winner. Flag the C++ answer in invalid and deletion, don’t close the question because of one bad (debatable but not my point) answer – caird coinheringaahing – 2020-12-26T13:48:45.360
OK, you've convinced me. I'll vote to re-open as soon as the C++ answer is deleted by a moderator (which should have been done in the first place rather than disqualifying it from the winning criteria)
– pppery – 2020-12-26T17:38:44.817And my flag was resolved without the answer being deleted, so this question is now in a chicken-egg situation leaving no resolution other than remaining closed. – pppery – 2021-01-08T19:19:06.213
@pppery What rule do you follow exactly that says to close a question if one answer violates its rules? Besides closing a question for zero practical reasons other than virtual points, all you have achieved is wasting of time. You can't reopen the question anyway, you aren't a mod. – Athari – 2021-01-09T14:29:07.293