vector tuple pair tie ignore

// c++23 compiles as :- g++ prog.cc -Wall -Wextra -std=gnu++2b -pedantic-errors -fstack-protector-all
//
// This example shows examples of pair, tuple and vector
//
#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <cstdlib>
#include <bits/stdc++.h>

#include <string>
#include <fstream>
#include <regex>

void f( std::vector<std::pair<int, int>>& p, int x)
{
    p.push_back(std::make_pair(1,x));
    p.push_back(std::make_pair(90,162));
    p.push_back(std::make_pair(11,12));
    p.push_back(std::make_pair(x,102));
}

std::tuple<std::string, std::string> t( std::string tagname, std::string value )
{
    return std::make_tuple( tagname, value );
}

std::optional<float> oFloat = std::nullopt;

// parses string input to an int or null
std::int32_t ParseStringToInt(std::string& arg)
{
    try
    {
        return { std::stoi(arg) };
    }
    catch (...)
    {
        std::cout << "cannot convert \'" << arg << "\' to int!\n";
        return -1;
    }

}

std::int32_t get_tag_value( std::string tag_to_fetch, std::tuple<std::string, std::string> tup) {
     std::regex pattern(".*" + tag_to_fetch + ".*");
     if (std::regex_match(get<0>(tup), pattern)) {
        return ParseStringToInt(std::get<1>(tup));
     }
     return -1;
}

int main(void)
{
    std::vector<std::pair<int, int> > p;
    f(p,67);

    // print the vector as it was made
    //
    for (auto x : p) {
        std::cout << x.first << " " << x.second << std::endl;
    }

    // sort this in order of greatest first index value
    //
    std::sort( begin( p ), end( p ), std::greater<std::pair<int, int>>() );
    for (auto x : p) {
      std::cout << "first "<< x.first << " second " << x.second << std::endl;
    }

    // now do the tuple
    //
    std::tuple<std::string, std::string> x = t("my_first_value", "2");
    std::string z;
    std::tie(std::ignore, z) = x;
    std::cout << z << std::endl;
    auto val = get_tag_value("my_first_value", x);
    std::cout << std::get<0>(x) << " tags value is " << val << std::endl;

    x = t("my_second_value", "20");
    std::tie(std::ignore, z) = x;
    std::cout << z << std::endl;
    val = get_tag_value("my_first_value", x);
    std::cout << "my_first_value tags value is " << val << std::endl;
    val = get_tag_value("my_second_value", x);
    std::cout << std::get<0>(x) << " tags value is " << val << std::endl;

    return 0;
}