Getting garbage when reading string from std::smatch - c++

Question

I'm trying to fix a memory issue, I think, for several hours now and I can't understand the issue of the problem.
I have a classes StaticTag and ExtendsTag that I create with result of std::smatch (<regex>). Method creating StaticTag always works, but method creating ExtendsTag never works. The only difference is regular expression which works all the time because the substring is matched. Problem here is even printing a captured group which mostly all the time gives me a garbage with suffix of correct string. Here is the code.
Execution of two methods find_static_tag and find_extends_tag (the latter does not work):
StaticTag static_tag;
if (Regex::find_static_tag(this->_content, static_tag)) {
}
ExtendsTag extends_tag;
if (Regex::find_extends_tag(this->_content, extends_tag)) {
}
Both methods presented below:
bool Regex::find_extends_tag(std::string in, ExtendsTag& tag) {
std::string pattern = "\\{%\\s*extends\\s+\"(\\S+)\"\\s*%\\}";
std::smatch match;
if (Regex::find_first(pattern, in, match)) {
std::cout << match[1] << std::endl;
tag = ExtendsTag(match[1], match.position(), match.length());
return true;
}
return false;
}
bool Regex::find_static_tag(std::string in, StaticTag& tag) {
std::string pattern = "\\{%\\s*static\\s+\"(\\S+)\"\\s*%\\}";
std::smatch match;
if (Regex::find_first(pattern, in, match)) {
std::cout << match[1] << std::endl;
tag = StaticTag(match[1], match.position(), match.length());
return true;
}
return false;
}
They need to match: {% static "style.css" %} and {% extends "master.html" %}.
Usually I got something like this instead of "master.html": �0e.html.
I think it might be memory issue, but I don't know where to start because two methods looks identical for me. It is not about creating objects of StaticTag and ExtendsTag, it fails printing match[1] in find_extends_tag method.
EDIT: Look like when I change from static to extends in the second method the result is the same. Is this something wrong with <regex> then?
Thank you for your help in advance!
The file I am trying to parse:
{% extends "master.html" %}
{% block content %}
<p>Hello ios/index.html</p>
<img src="{% static "html-css.png" %}"/>
{% endblock %}
EDIT 2:
Not sure why it started to work. I took out implementation of Regex::find_first(pattern, in, match) and put it directly in find_static_tag and find_extends_tag and it started to work correctly.
Here is implementation of find_extends_tag that works always:
bool Regex::find_extends_tag(std::string in, ExtendsTag& tag) {
std::smatch match;
if (std::regex_search(in, match, std::regex("\\{%\\s*extends\\s+\"(\\S+)\"\\s*%\\}"))) {
tag = ExtendsTag(match[1], match.position(), match.length());
return true;
}
return false;
}
Not sure what's the difference here.