update_json_in_place_examples.cpp

// Copyright 2013-2025 Daniel Parker
// Distributed under Boost license

#include <jsoncons/json.hpp>
#include <iostream>

using namespace jsoncons;

class string_locator : public jsoncons::default_json_visitor
{
    char* data_;
    std::size_t length_;
    std::vector<std::string> path_;
    std::string from_;
    std::vector<std::string> current_;
    std::vector<std::size_t> positions_;
public:
    using jsoncons::default_json_visitor::string_view_type;

    string_locator(char* data, std::size_t length,
        const std::vector<std::string>& path,
        const std::string& from)
        : data_(data), length_(length),
          path_(path), from_(from)
    {
    }

    const std::vector<std::size_t>& positions() const
    {
        return positions_;
    }
private:
    bool visit_begin_object(semantic_tag, const ser_context&, std::error_code&) override
    {
        current_.emplace_back();
        return true;
    }

    bool visit_end_object(const ser_context&, std::error_code&) override
    {
        current_.pop_back();
        return true;
    }

    bool visit_key(const string_view_type& key, const ser_context&, std::error_code&) override
    {
        current_.back() = std::string(key);
        return true;
    }

    bool visit_string(const string_view_type& value,
        jsoncons::semantic_tag,
        const jsoncons::ser_context& context,
        std::error_code&) override
    {
        if (path_.size() <= current_.size() && std::equal(path_.rbegin(), path_.rend(), current_.rbegin()))
        {
            if (value == from_)
            {
                positions_.push_back(context.position()+1); // one past quote character

            }
        }
        return true;
    }
};

void update_json_in_place(std::string& input,
    const std::vector<std::string>& path,
    const std::string& from,
    const std::string& to)
{
    if (input.size() > 0)
    {
        string_locator locator(&input[0], input.size(), path, from);
        jsoncons::json_string_reader reader(input, locator);
        reader.read();

        for (auto it = locator.positions().rbegin(); it != locator.positions().rend(); ++it)
        {
            input.replace(*it, from.size(), to);
        }
    }
}

int main()
{
    std::cout << "\njson update in place examples\n\n";

    std::string input = R"(
{
    "Cola" : {"Type":"Drink", "Price": 10.99},"Water" : {"Type":"Drink"}, "Extra" : {"Cola" : {"Type":"Drink", "Price": 8.99}}
}
)";

    try
    {
        std::cout << "(original)\n" << input << "\n";
        update_json_in_place(input, {"Cola", "Type"}, "Drink", "SoftDrink");

        std::cout << "(updated)\n" << input << "\n";
    }
    catch (std::exception& e)
    {
        std::cout << e.what() << "\n";
    }

    std::cout << '\n';
}