cannot use operator[] with number

[brainmixxx]

Hello, I have unfortunately a problem with which I come no further:

I have data in the form of a list of multiple objects and I want to create json :: array's from it.

Input:
{ "candles":[ { "close":"470.0380", "epoch":1489306680, "high":"470.0954", "low":"469.8577", "open":"469.8577" }, { "close":"469.3634", "epoch":1489306740, "high":"470.0012", "low":"469.2554", "open":"470.0012" }, { "close":"469.4181", "epoch":1489306800, "high":"469.6009", "low":"469.1578", "open":"469.3178" } ], "echo_req": { "count":3, "end":"latest", "style":"candles", "ticks_history":"R_50" }, "msg_type":"candles" }

I would like the following output:
{ "open": {12, 21, 1}, "low": {23, 32, 2}, "high": {34, 43, 3} }

My approach is as follows:
json jCandles = { {"open", json::array()}, {"high", json::array()}, {"low", json::array()} }; for (unsigned int i = 0; i != jObj["candles"].size(); ++i) { jCandles["open"] += jObj["candles"][1]["open"]; }

i get following error:

terminate called after throwing an instance of 'std::domain_error' what(): cannot use operator[] with number

and with jCandles["open"].push_back(jObj["candles"][1]["open"]);
it says cannot use push_back() with number

I do not know how to handle the error. Can someone help me?

[nlohmann]

I'm not sure about the actual transformation of your JSON values, but I can compile your code without problems:

#include <json.hpp>

using json = nlohmann::json;

int main()
{
    json jObj = R"({ "candles":[ { "close":"470.0380", "epoch":1489306680, "high":"470.0954", "low":"469.8577", "open":"469.8577" }, { "close":"469.3634", "epoch":1489306740, "high":"470.0012", "low":"469.2554", "open":"470.0012" }, { "close":"469.4181", "epoch":1489306800, "high":"469.6009", "low":"469.1578", "open":"469.3178" } ], "echo_req": { "count":3, "end":"latest", "style":"candles", "ticks_history":"R_50" }, "msg_type":"candles" })"_json;

    json jCandles = {
        {"open", json::array()},
        {"high", json::array()},
        {"low", json::array()}
    };
    for (unsigned int i = 0; i != jObj["candles"].size(); ++i)
    {
        jCandles["open"] += jObj["candles"][1]["open"];
    }

    std::cout << std::setw(2) << jCandles << std::endl;
}

Output:

{
  "high": [],
  "low": [],
  "open": [
    "470.0012",
    "470.0012",
    "470.0012"
  ]
}

[brainmixxx]

@nlohmann Thank you for the fast answer!
I think I've found the cause. I have built a class where I have created the list. Now I have the function outsourced and it works.

My class looks like this:

class candle_values {
public:
	json jCandles = {
		{"open", json::array()},
		{"high", json::array()},
		{"low", json::array()},
		{"close", json::array()},
		{"date", json::array()}
		};
	bool isNewCandle;`

	void new_list(json jObj){
		for (unsigned int i = 0; i != jObj["candles"].size(); ++i) {
			std::cout << "jC: " << jObj["candles"][i]["open"] << std::endl;
			jCandles["open"] += jObj["candles"][i]["open"];
		}
		std::cout << std::setw(2) << jCandles << std::endl;
		isNewCandle = false;
	}

Because of another class I work here with pointer and think that it must be because of it. Will check this today and write again.

[nlohmann]

Can I close this issue?

[brainmixxx]

Yes sure! Many thanks for the help!

[nlohmann]

No worries!