在 C++ 中创建一个 json 数组
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Create a json array in C++
提问by Hannes
So im trying to create a json Object in c++ dynamically. I want to add a timestamp and then an array with the data included.
所以我试图在 C++ 中动态创建一个 json 对象。我想添加一个时间戳，然后添加一个包含数据的数组。
So thats what my json String would look like :
所以这就是我的 json 字符串的样子：
{
"timestep": "2160.00",
"vehicles": [
{
"id": "35092_35092_353",
"x": "6.988270",
"y": "50.872139",
"angle": "-20.812787",
"type": "passenger_P_14_1",
"speed": "0.000000",
"pos": "4.600000",
"lane": "4.600000",
"slope": "4.600000"
},
{
"id": "35092_35092_353",
"x": "6.988270",
"y": "50.872139",
"angle": "-20.812787",
"type": "passenger_P_14_1",
"speed": "0.000000",
"pos": "4.600000",
"lane": "4.600000",
"slope": "4.600000"
},
{
"id": "35092_35092_353",
"x": "6.988270",
"y": "50.872139",
"angle": "-20.812787",
"type": "passenger_P_14_1",
"speed": "0.000000",
"pos": "4.600000",
"lane": "4.600000",
"slope": "4.600000"
}
]
}
Im totally new to C++ and im using the Casablanca ( C++ REST SDK) package. So im having a really hard time producing the code. And i cant find any working solutions. I found this on the wiki
我是 C++ 的新手，我使用的是 Casablanca（C++ REST SDK）包。所以我很难生成代码。而且我找不到任何有效的解决方案。我在维基上找到了这个
Create a JSON object:
创建一个 JSON 对象：
json::value obj;
obj[L"key1"] = json::value::boolean(false);
obj[L"key2"] = json::value::number(44);
obj[L"key3"] = json::value::number(43.6);
obj[L"key4"] = json::value::string(U("str"));
and that works for me. But how do i create an array?
这对我有用。但是我如何创建一个数组？
i tried several things but nothing worked. Maybe theres a better package? But as far as i understood its an official micorosft package for json and http.
我尝试了几件事，但没有任何效果。也许有更好的包？但据我所知，它是用于 json 和 http 的官方 micorosft 包。
Help would be really nice!
帮助会非常好！
采纳答案by FatalFlaw
There are 2 mechanisms. If you are used to std c++ libraries, this should look familiar. Element vector is derived from std::vector.
有2种机制。如果您习惯于 std c++ 库，这应该看起来很熟悉。元素向量源自 std::vector。
json::value::element_vector e;
// the first item in the pair is the array index, the second the value
e.push_back(std::make_pair(json::value(0), json::value(false)));
e.push_back(std::make_pair(json::value(1), json::value::string(U("hello"))));
json::value arr(e);
And, if you prefer a cleaner look, and can accept a less efficient compiled result:
而且，如果您更喜欢更简洁的外观，并且可以接受效率较低的编译结果：
json::value arr;
arr[0] = json::value(false);
arr[1] = json::value(U("hello"));
From your message you have tried a bunch of stuff. If you have tried mechanisms like these but they didn't work, give us a sample program that demontrates the failure and we'll have a crack at it.
根据您的消息，您尝试了很多东西。如果您尝试过类似的机制但它们不起作用，请给我们一个演示失败的示例程序，我们将对其进行破解。
To get the basic structure in your file above:
要获取上述文件中的基本结构：
json::value vehicles;
vehicles[0] = // 1st vehicle object
vehicles[1] = // 2nd vehicle object
// etc
json::value root;
root[L"timestep"] = json::number(2160.0);
root[L"vehicles"] = vehicles;
回答by Nhon Nguyen
Here's how to create an array dynamically using vector. Assume that you have 10 vehicles to add.
以下是如何使用vector. 假设您要添加 10 辆车。
std::vector<web::json::value> arrayVehicles;
for(int i = 0; i < 10; i++)
{
web::json::value vehicle;
std::string vehicleID = "id_prefix_" + std::to_string(i);
vehicle["id"] = web::json::value::string(vehicleID);
vehicle["x"] = web::json::value::number(6.988270);
vehicle["y"] = web::json::value::number(50.872139);
arrayVehicles.push_back(vehicle);
}
web::json::value myJSON;
myJSON["vehicles"] = web::json::value::array(arrayVehicles);
回答by Marius Bancila
You could put it like this:
你可以这样说：
json::value vehicle1;
vehicle1[L"id"] = json::value::string(L"35092_35092_353");
vehicle1[L"x"] = json::value::number(6.988270);
vehicle1[L"y"] = json::value::number(50.872139);
json::value vehicle2;
vehicle2[L"id"] = json::value::string(L"35092_35092_353");
vehicle2[L"x"] = json::value::number(1.23456);
vehicle2[L"y"] = json::value::number(6.78901);
json::value vehicles;
vehicles[L"timestamp"] = json::value::number(2160);
vehicles[L"vehicles"] = json::value::array({vehicle1, vehicle2});
回答by davidhigh
Here is another method to produce a json array in Casablanca:
这是在卡萨布兰卡生成 json 数组的另一种方法：
int size = 3;
web::json::value yourJson;
yourJson[U("vehicles")] = web::json::value::array(size);
yourJson[U("vehicles")].as_array()[0] = web::json::value(U("some entry"));
yourJson[U("vehicles")].as_array()[1] = web::json::value(U("another entry"));
//...
回答by Dmitry
If you wish to use the array as an answer on a received http_request (in case below it's a http_request request), you are free to use the following snippet of code as an example:
如果您希望使用该数组作为收到的 http_request 的答案（如果下面是 a http_request request），您可以随意使用以下代码片段作为示例：
json::value answer;
auto array = answer.array();
for (size_t i = 0; i < GenFile.GetNumberOfCurves(); i++)
{
web::json::value vehicle;
vehicle[L"smth"] = web::json::value::number(WhatEverArray[i].whatever());
array[i] = vehicle;
}
request.reply(status_codes::OK, array);
