How to extract html tag name from std::string in C++?

Question

In this example:

#include <iostream>
#include <fstream>
#include <string>
#include <deque>
#include <sstream>


struct tag {
    bool isOpening;
    std::string name;
};

void print(const std::deque<tag> &deq){
    for(const auto &i : deq){
        std::cout << i.name << std::endl;
    }
}

int main() {
//    std::ifstream infile("a.html");
//    std::stringstream buffer;
//    buffer << infile.rdbuf();
//    std::string buf = std::move(buffer.str());
    std::deque<tag> deq;
    std::string buf = "<html>\n"
                      "\n"
                      "<body>\n"
                      "    <h1>Hello <b>world</b></h1>\n"
                      "</body>\n"
                      "\n"
                      "</html>";

    size_t pos = 0;
    while ((pos = buf.find('<', pos)) != std::string::npos) {
        bool isOpening = true;
        if(buf[pos+1] == '/'){
            isOpening = false;
            pos++;
        }
        std::string token = buf.substr(pos, buf.find('>', pos));
        deq.push_back({isOpening, token});
        pos++;
    }

    print(deq);
}

I would like to parse for each tag its name and whether it is opening or not. But the output is:

<html
<body>
    <h
<h1>Hello <b>world</b>
<b>world</b></h1>
</body>

</ht
/b></h1>
</body>

</html>
/h1>
</body>

</html>
/body>

</html>
/html>

which is of course not correct. So what am I doing wrong?

Jacob Steinebronn · Accepted Answer · 2022-03-01 19:36:36Z

1

the substr function in c++ takes in two arguments: The position, and the length of the substring, and not the start and end positions. So you're basically having almost all of the substrings be for the entire string, which is why you see so much repeated output. You're really just wanting to take that substr command and change it to

 buf.substr(pos, buf.find('>', pos)-pos-1);

Hope that works!

answered Mar 1, 2022 at 19:36

Jacob Steinebronn

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