Using JSON

This example demonstrates how to use the basic functionality of SG++ JSON API.

The goal of this API is to facilitate generation and parsing of complex configuration files. Also it permits easy but limited object serialization functionality.

#include <sgpp/base/tools/json/JSON.hpp>
#include <sgpp/base/tools/json/TextNode.hpp>
#include <sgpp/base/tools/json/json_exception.hpp>
 
int main(int argc, char **argv) {
  try {

We first create an empty JSON object

    json::JSON configuration;

Then we introduce the following JSON structure:

{
    parent:{
        "t1":"v1";
        "t2":"v2";
        "list1":["tv1",96.0,"tv2"]
            };
    "textAttr1":"text1";
    "numVal1":36.0
}

As you can see in the code below, methods to append new entries support chaining for convenience.

    configuration.addDictAttr("parent")
        .addTextAttr("t1", "v1")
        .addTextAttr("t2", "v2")
        .addListAttr("list1")
        .addTextValue("tv1")
        .addIdValue(96.0)
        .addTextValue("tv2");
    configuration.addTextAttr("textAttr1", "text1").addIDAttr("numVal1", 36.0);

You can conveniently get and set values inside the JSON object using Key/Value notation.

This call gets the string representation of the second entry (96.0) in list1 of dictionary parent.

    std::cout << "value: " << configuration["parent"]["list1"][1].get() << std::endl;

This call sets the second entry (96.0) in list1 of dictionary parent to the double value 7 and then prints its string representation.

    configuration["parent"]["list1"][1].setDouble(7);
    std::cout << "value: " << configuration["parent"]["list1"][1].get() << std::endl;

You can also try to obtain a typed representation of an entry. Conversion is performed automatically and may result in an exception if it can't be converted.

    std::cout << "value: " << configuration["parent"]["list1"][1].getDouble() << std::endl;

Next we demonstrate erasing values.

Here we erase numVal1 from the top level of the configuration object.

    configuration["numVal1"].erase();

Now we erase the dictionary named parent from the the configuration object. Note that the object that is erased is returned to us by the erase operation. All Objects inside a JSON object are represented internally as an object of type Node"

    std::unique_ptr<json::Node> parentNode = configuration["parent"].erase();

    configuration.addDictAttr("parentparent").addAttribute("parent", std::move(parentNode));

Serialization (i.e. writing of a standard compatible json file) is also possible.

    configuration.serialize("write.json");

We can also read a JSON file by passing it's path to the constructor of a JSON object

    json::JSON reread("write.json");
  } catch (json::json_exception &e) {
    std::cout << e.what() << std::endl;
  }
 
  return 0;
}