Looking for C++ Regex optionally including whitespaces - regex

Question

I'm having a string like
"<firstname>Anna</firstname>"
or
"<firstname>Anna Lena</firstname>"
and I want to use Regex to get the name out of it (so only "Anna" or "Anna Lena"). Currently I'm using:
std::regex reg1 ("(<firstname>)([a-zA-Z0-9]*)(</firstname>)");
and
std::regex_replace (std::back_inserter(result), input.begin(), input.end(), reg1, "$2");
which works well with only one name, but apparently it misses anything after that because it doesn't consider whitespaces. Now I've tried adding \s like ((([a-zA-Z0-9]*)|\s)*) but my IDE (Qt) tells me, that that \s is an unknown escape sequence.
Right now, "<firstname>Anna Lena</firstname>" results in "<firstname>Anna".
How do I solve this in an elegant way?

Answer 1

Use a reluctant quantifier for dot:
std::regex reg1 ("<firstname>(.*?)</firstname>");
Alternately, you can use "not a right angle":
std::regex reg1 ("<firstname>[^<]*</firstname>");
Note that I removed the unnecessary groups around the tag literals, so the target is now group 1 (your regex captured it in group 2).

Answer 2

It seems to me you have an issue with the back_converter in a regex_replace that inserts new elements automatically at the end of the container.
I suggest adding \s to the character class and matching the strings instead of reassigning the vector strings.
Here is a demo of my approach:
#include <iostream>
#include <regex>
using namespace std;
int main() {
std::vector<std::string> strings;
strings.push_back("<firstname>Anna</firstname>");
strings.push_back("<firstname>Anna Lena</firstname>");
std::regex reg("(<firstname>)([a-zA-Z0-9\\s]*)(</firstname>)");
for (size_t k = 0; k < strings.size(); k++)
{
smatch s;
if (std::regex_match(strings[k], s, reg)) {
strings[k] = s[2];
std::cout << strings[k] << std::endl;
}
}
return 0;
}
Output:
Anna
Anna Lena