ordered elements with jsoncpp

Question

I use jsoncpp to parse my config.json. It library use std::map to contain pairs key:value. Map is unordered container. Now I need to parse elements in the same order in which they are in the file (do not ask why, it's not my whimsy).

I did some searching and I found that

you can write your own parser or rewrite jsoncpp to use list instead of map.

Can I really replace the list with a map in jsoncpp?

Or, maybe, you give me some idea, how I can save order of elements when I parse file with jsoncpp?

This information doesn't help you with your problem, but [`std::map`](http://en.cppreference.com/w/cpp/container/map) is definitely an ordered container, however it might not be ordered the way you like it. — Some programmer dude, Sep 08 '15 at 13:54
You could use json-spirit to parse it, I think it's configurable what datatypes it uses? FWIW you might have a hard time with this because I think JSON is specified such that there is no logical order to the key:value pairs. If you really need to have it in a list or a vector, you might be best off just... taking the pairs out of the map and putting them in a list or vector. — Chris Beck, Sep 08 '15 at 13:55
Re *do not ask why, it's not my whimsy* -- If it's someone else's whimsy, tell that person that they are using JSON incorrectly. A JSON object has no order (which means any order used by an implementation is okay). If you wanted something in which order matters, use a JSON array. It's the duty of a responsible programmer to push back on bad requirements. — David Hammen, Sep 08 '15 at 17:13
Cou certainly *can* replace `std::map` with `std::list`, but most probably you'd have to also modify `Json::Value::operator[]` to perform linear search instead of map lookup, at least. — el.pescado - нет войне, Sep 09 '15 at 06:28

score 0 · Answer 1 · answered Jul 14 '22 at 05:32

0

std::ifstream i("input.json");
auto j = nlohmann::ordered_json::parse(i);
std::cout << j.dump(2) << std::endl;

answered Jul 14 '22 at 05:32

Qiuren

19
3

score -1 · Answer 2 · edited May 23 '17 at 12:14

I think you need to use another container rather than QMap in jsoncpp that maintain insertion order of values

unfortunately Qt doesn't have such a data type and you have to do it on your own because neither QMap nor QHash maintains insertion order

if you can use Boost it has a unordered_map http://www.boost.org/doc/libs/1%5F37%5F0/doc/html/unordered.html 1

See:

QMap but without sorting by key 1

Make Map Key Sorted According To Insert Sequence 1

A std::map that keep track of the order of insertion?1

ordered elements with jsoncpp

2 Answers2