[answered]Read key1 from .value example

[Diablillowilly]

I was trying to use the library to read and parse a json post which I receive, so I just want to read each value, but , I dont know how to read a value inside an object. In this example I would like to access the value of key1 or key2, I have tryed things like object.key1 or object:key1, but none of them worked.

[nlohmann]

Assume you read this JSON value:

{
  "key1": true,
  "key2": 2
}

Then you can access the values with:

bool k1 = j["key1"];
int k2 = j["key2"];

(assuming you parsed your JSON value to json j).

If you need more information, please provide some example code, the error you experience and your expected behavior.

[Diablillowilly]

I get a json in a string from a http post

`std::string input=
"{

    {\"str\", \"helloworld\"},
    {\"int\", 24},
    {\"object\", {{\"key1\", 1}, {\"key2\", 2}, {\"subobject\",{\"subkey1\", 1}, {\"subkey2\", 2}}}},
}";`

and after that I parse them like this so I get rid of the backslash:
nlohmann::json j = nlohmann::json::parse(input);

and I am reading values at the same level as str or int by making:

std::string str = j.value("str", "");
 int str = j.value("int", 0);

but what do I have to do If I want to read key1/2 or subkey1/2?

EDIT

And is there any difference between int k2 = j["key2"]; or int k2 = j.value("key2", 0);?
Whaat would happen if I used the first method and k2 didnt exist?

[nlohmann]

• Right now, value does not support nesting. That is, you can only apply it to an object to retrieve a primitive value.
• j["key"] adds key "key" if it does not exist and stores null. If j is const, the behavior is undefined for nonexisting keys.
• j.at("key") throws an exception if key "key" does not exist and will not change the object.

[cronnosli]

"but what do I have to do If I want to read key1/2 or subkey1/2?"

If you want to read a subkey you could access the json object as it is like a multilevel array:

int value = j["object"]["subobject"][subkey1].get<int>();

Or by walk throw in a STL manner:

for (json::iterator it = j["object"].begin(); it != j["object"].end(); ++it) {
  std::cout << it.key() << " : " << it.value() << "\n";
}

But with a loop you would need to interact each subobject in a nested loop!

[Diablillowilly]

I have finally made it like this:

if (!j["object"]["subobject"]["subkey"].is_null()) { return j["object"]["subobject"]["subkey"]; }

So I check if it exists, and then I read it. Thank you very much for your help