std::string to JSON parsing

[cxxboy]

I have a request coming in as JSON, Example:
curl --header "Content-Type: application/json" -d '{"hello":123}' http://127.0.0.1:8766/poster

The std::string contains the {"Hello":123} I can able to print out.
But, How can I parse that as JSON object?

Here is something I tried out:

using json = nlohmann::json;
json::parser_callback_t json_cb = [](int depth, json::parse_event_t event, json& parsed){
	if(event == json::parse_event_t::key and parsed == json("hello")){
		return true;
	}else{
		return false;
	}
};
// Here, INPUT_TEXT is std::string type (which is converted from char* to std::string from raw socket read() )
auto parsed_json = json::parse(INPUT_TEXT, json_cb);
std::cout << parsed_json << std::endl;

For the note, parsed_json["hello"]; also gives me null (does not work)

But this keeps giving me NULL. Can someone help me figure this out? Or is there any other way I can parse this other than callback (I dont fully understand the use of callbacks in the json::parser, Im copy-pasting from docs?

[nlohmann]

You can just call auto parse_json = json::parse(INPUT_TEXT);. The callback is optional, and you may only need it if you want to filter values while parsing.

[nlohmann]

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