reading arrays of json objects with nlohmann c++ library

Question

I am ok using this syntax with the nlohmann library

{
 "key1": {"subKey1": "value11", 
          "subKey2": "value12"},
 "key2": {"subKey1": "value21", 
          "subKey2": "value22"}
}

But I have a new file, which is valid json too (I checked) and is written this way, it is made of a single array of repetitive objects. My code will require to look through those objects and check values inside them individually:

[
 {"key1": "value11", 
  "key2": "value12"},
 {"key1": "value21", 
  "key2": "value22"}
]

I used to read my json files this way:

  #include "json.hpp"
  
  nlohmann::json topJson;
  nlohmann::json subJson;

    if(topJson.find(to_string("key1")) != topJson.end())
    {
        subJson = topJson["key1"]; 
        entity.SetSubKeyOne(subJson["subKey1"]);
    }

But this won't work with my new file syntax. How can I access these repetitive objects and tell nlohmann that my objects are inside an array? More precisely, how would I be able to reach (for example) "value22" with this file syntax?

Thanks!

You can walk an `nlohmann::json` array just like you walk a regular array: use range-for, iterators, or just access by index. — Botje, Aug 13 '20 at 15:55

score 3 · Accepted Answer · answered Jan 29 '21 at 04:17

You can try this:

std::string ss= R"(
{
    "test-data":
    [
        {
            "name": "tom",
            "age": 11
        },
        {
            "name": "jane",
            "age": 12
        }
    ]
}
)";

json myjson = json::parse(ss);

auto &students = myjson["test-data"];

for(auto &student : students) {
    cout << "name=" << student["name"].get<std::string>() << endl;
}

reading arrays of json objects with nlohmann c++ library

1 Answers1