C++ to extract data between two strings

I am looking for a c++ code which can extract some specific content from a file example.txt between two strings and ignore the rest content. for example a file example.txt have below lines

xyz
abc
['Content','en']],
<html>hi this is a line <br></html>
',true], 
suzi 20

I want to extract code between ['Content','en']], and ',true], which means

<html>hi this is a line <br></html>

Please note that i am not expert in programming and using dev++ compiler

Solution

The simplest idea is to read the file into a string, and then extract the content:

#include <string>
#include <sstream>

std::string extract(std::string const& tag_begin, std::string const& tag_end, std::istream& input)
{
    // file stream -> in memory string
    std::string filedata((std::istreambuf_iterator<char>(input)), std::istreambuf_iterator<char>());

    // find content start and stop
    auto content_start = filedata.find(tag_begin);
    if (content_start == std::string::npos) {
        return ""; // error handling
    }
    content_start += tag_begin.size();
    auto content_end   = filedata.find(tag_end, content_start);
    auto content_size  = content_end - content_start;

    // extract (copy) content to other string
    auto content = filedata.substr(content_start, content_size);
    return content;
}

live demo

Then, you'll need to adapt this generic solution to your needs.