Using regex in C++ to transform a string into JSON

main.cpp

/**
This should transform the string:
- name=Maria, grades-90,age/25?university-UCL,surname=Hill,grades//85,graduates=5%ID=356231, graduates-7,grades=78//graduates=3

Into:
{
   "output":{
      "university":"UCL",
      "students":{
         "name":"Maria",
         "surname":"Hill",
         "age":25,
         "ID":356231,
         "grades":[
            90,
            85,
            78
         ]
      },
      "graduates":15
   }
}

clag flags: -O3 -std=c++2a -DFMT_HEADER_ONLY=1
CE: https://godbolt.org/z/DSElLr
*/


#include <iostream>
#include <regex>
#include <string> // std::string, std::stoi
#include <vector>
#include <optional>
#include <cstdio>
#include <fmt/format.h>

std::string formattedOutput(const std::string &input) {
    auto getData = [&input](std::string str) -> std::optional<std::string> {
        try {
            std::regex reg{str + ".+?(\\w+)"};               
            std::smatch sm;

            if (std::regex_search(input, sm, reg)) {
                return { sm[1] }; 
            }
        } catch (const std::regex_error& e) {
            std::cout << "regex_error caught: " << e.what() << '\n';
        }

        return {};
    };

    auto getGrades = [&input]() {
        std::string localInput{input};
        std::string grades{};
        std::regex r(R"(grades.+?(\w+))");
        std::smatch sm;

        while(regex_search(localInput, sm, r)) {
            if (!grades.empty()) {
                grades += ", ";
            }

            grades += sm[1];
            localInput = sm.suffix();
        }

        return grades;
    };

    //@Todo: move this and the above function to one
    auto getGraduatesTotal = [&input]() {
        std::string localInput{input};
        int total{};
        std::regex r(R"(graduates.+?(\w+))");
        std::smatch sm;

        while(regex_search(localInput, sm, r)) {
            total += std::stoi(sm[1]);
            localInput = sm.suffix();
        }

        return total;
    };

    std::string output =    R"({{)"
                            R"(   "output":{{)"
                            R"(      "university":"{}",)"
                            R"(      "students":{{)"
                            R"(         "name":"{}",)"
                            R"(         "surname":"{}",)"
                            R"(         "age":{},)"
                            R"(         "ID":{},)"
                            R"(         "grades":[{}])"
                            R"(      }},)"
                            R"(      "graduates":{})"
                            R"(   }})"
                            R"(}})";

    return fmt::format(output, 
        *getData("university"),
        *getData("name"),
        *getData("surname"),
        *getData("age"),
        *getData("ID"),
        getGrades(),
        getGraduatesTotal()
    );
}


int main() 
{
    const std::string input{R"(name=Maria, grades-90,age/25?university-UCL,surname=Hill,grades//85,graduates=5%ID=356231, graduates-7,grades=78//graduates=3)"};
    std::cout << formattedOutput(input) << '\n';
}