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Create json array using boost property_tree

I am having problems creating a json array using boost library, a property tree in C ++.

I used this link , especially this part

ptree pt;
ptree children;
ptree child1, child2, child3;


child1.put("childkeyA", 1);
child1.put("childkeyB", 2);

child2.put("childkeyA", 3);
child2.put("childkeyB", 4);

child3.put("childkeyA", 5);
child3.put("childkeyB", 6);

children.push_back(std::make_pair("", child1));
children.push_back(std::make_pair("", child2));
children.push_back(std::make_pair("", child3));

pt.put("testkey", "testvalue");
pt.add_child("MyArray", children);

write_json("test2.json", pt);

leads to:

{
    "testkey": "testvalue",
    "MyArray":
    [
        {
            "childkeyA": "1",
            "childkeyB": "2"
        },
        {
            "childkeyA": "3",
            "childkeyB": "4"
        },
        {
            "childkeyA": "5",
            "childkeyB": "6"
        }
    ]
}

But what should I do if I want to achieve a simple array without any object containing it? Like this:

[
    {
        "childkeyA": "1",
        "childkeyB": "2"
    },
    {
        "childkeyA": "3",
        "childkeyB": "4"
    },
    {
        "childkeyA": "5",
        "childkeyB": "6"
    }
]

Thank you very much.

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2 answers


Finally, I have not found a solution using the boost library. But this can be achieved with cpprestsdk ("Casablanca").

Example:

using namespace web;
using namespace web::http;
using namespace web::http::client;
using namespace web::json;

void testFunction(http_request req)
{

   // only to test the serialization of json arrays
   json::value elmnt1;
   elmnt1[L"element"] = json::value::string(U("value1"));

   json::value elmnt2;
   elmnt2[L"element"] = json::value::string(U("value2"));

   json::value response;                     // the json array
   response[0] = elmnt1;
   response[1] = elmnt2;

   string outputStr = utility::conversions::to_utf8string(shifts.serialize());

   req.reply(200, outputStr, "application/json");
};


And this leads to

[  
  {  
     "element":"value1"
  },
  {  
     "element":"value2"
   }
]
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The Boost documentation for JSON support is just a few lines:

http://www.boost.org/doc/libs/1_63_0/doc/html/property_tree/parsers.html#property_tree.parsers.json_parser



The property tree dataset is not injected and does not support arrays as such . So the following JSON / property tree mapping is used:

  • JSON objects are mapped to nodes. Each property is a child node.
  • JSON arrays are mapped to nodes. Each element is a child node with an empty name. If a node has named and unnamed child nodes, it cannot be matched against the JSON representation.
  • JSON values ​​are mapped to nodes containing this value. However, all types of information are lost; numbers as well as literals "null", "true" and "false" are simply matched against their string form.
  • Properties tree nodes containing both child nodes and data cannot be displayed.

JSON round-trip, except for loss of type information.

Underline mine

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