items() method does not follow order of json message

[denesh-globotix]

What is the issue you have?

Thank you for this library, it has been a real help! I am trying to pass JSON into a c++ code from another Javascript code and everything is working well. One thing I observed however is that the c++ iterator method seems to ignore the order that the JSON keys are in.

Please describe the steps to reproduce the issue.

In the print statement above, cleaning_zone_1 is the first key but when printing out the keys using the items() method the order gets changed for some reason

Can you provide a small but working code example?

    // This is the javascript code
   recipe_information = {"cleaning_zone_1":{"coordinates":"[[4.496000216007235, -3.773714192935398], [6.224000241756441, 1.7668573181969796], [2.630857331071582, 3.6868573468072077]]","vacuum":"0","roller":"0","gutter":"0"},"cleaning_zone_2":{"coordinates":"[[-0.6742855753217418, -4.322285629681177], [5.744000234603883, -3.965714195796421], [2.205714467593603, -6.324571373803275]]","vacuum":"1","roller":"0","gutter":"0"},"cleaning_zone_0":{"coordinates":"[[0.8754287334850862, -3.3348570435387743], [6.361143100942885, -0.2628569977624069], [3.7280002045631413, 1.7120001745224003]]","vacuum":"1","roller":"0","gutter":"0"}}

    // This is the c++ code
    auto j3 = json::parse(recipe_information);
    for (auto &el : j3.items())
    {
        std::cout << "key: " << el.key() << ", value:" << el.value() << '\n';
    }

What is the expected behavior?

I was under the impression that the first key, el.key() should have printed out cleaning_zone_1.

And what is the actual behavior instead?

Instead, cleaning_zone_0 is printed out

Which compiler and operating system are you using?

• Compiler: gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
  Copyright (C) 2019 Free Software Foundation, Inc.
  This is free software; see the source for copying conditions. There is NO
  warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

• Operating system: Ubuntu 20.04

Which version of the library did you use?

I'm sorry, i'm new to this and am not sure which library it is using. This is listed as part of my ROS dependency which I believe installs from the ROS build farm as listed here: https://index.ros.org/d/nlohmann-json-dev/

• latest release version 3.10.5
• other release - please state the version: ___
• the develop branch

[nlohmann]

See https://json.nlohmann.me/features/object_order/