C++ unknown escape sequences on regex + groups captured by half - c++

Question

I'm trying to use the following regex
(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?:(\/[^\s?#]+)([?][^\s#]+)?)?([#]\S*)?
on C++ like this:
#include <iostream>
#include <string>
#include <regex>
int main() {
std::string str("rtsp://3333:1232#hellowebsite.com:2222");
std::regex r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?:(\/[^\s?#]+)([?][^\s#]+)?)?([#]\S*)?");
std::smatch m;
std::regex_search(str, m, r);
std::cout << str << std::endl;
for(auto v: m) std::cout << v << std::endl;
}
To match rtsp or http URLs, but this is the output of compilation + running:
main.cpp:7:33: warning: unknown escape sequence '\/' [-Wunknown-escape-sequence]
std::regex r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?...
^~
main.cpp:7:35: warning: unknown escape sequence '\/' [-Wunknown-escape-sequence]
std::regex r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?...
^~
main.cpp:7:43: warning: unknown escape sequence '\s' [-Wunknown-escape-sequence]
std::regex r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?...
^~
main.cpp:7:46: warning: unknown escape sequence '\/' [-Wunknown-escape-sequence]
std::regex r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?...
^~
main.cpp:7:60: warning: unknown escape sequence '\s' [-Wunknown-escape-sequence]
std::regex r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?...
^~
main.cpp:7:62: warning: unknown escape sequence '\/' [-Wunknown-escape-sequence]
std::regex r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?...
^~
main.cpp:7:88: warning: unknown escape sequence '\/' [-Wunknown-escape-sequence]
...r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?:(\/[^\s?#]+)([...
^~
main.cpp:7:92: warning: unknown escape sequence '\s' [-Wunknown-escape-sequence]
...r("(https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?:(\/[^\s?#]+)([...
^~
main.cpp:7:105: warning: unknown escape sequence '\s' [-Wunknown-escape-sequence]
...\s#]+)?)?([#]\S*)?");
^~
main.cpp:7:118: warning: unknown escape sequence '\S' [-Wunknown-escape-sequence]
...\S*)?");
^~
10 warnings generated.
 ./main
rtsp://3333:1232#hellowebsite.com:2222
rtsp://3333:1232#helloweb
rtsp
3333:1232
helloweb
check here..
First of all, why I'm getting unknown escape sequences? \\, \s and etc are pretty known.
Most importantly, why do I get these unfinished groups? It works fine on regex online testers.

Answer 1

Especially when you're doing regexes, raw string literals are your friend. So, as a starting point, I'd do something like this:
std::regex r(R"--((https?|rtsp):\/\/(?:([^\s#\/]+?)[#])?([^\s\/:]+)(?:[:]([0-9]+))?(?:(\/[^\s?#]+)([?][^\s#]+)?)?([#]\S*)?)--");
If you really don't want to use raw string literals, the starting point is to note that a back-slash in a C++ string introduces an escape sequence, so when you want the literal to actually contain a back-slash you need to use two back-slash characters in a row, so (at bare minimum) you need to convert those, so it starts something like this:
std::regex r("(https?|rtsp):\\/\\/(?:
...continuing for all the other back-slashes it contains. There might be a bit more to do after that, but that's the minimum that it's immediately obvious you need to do.