JSONCPP Writing to files - c++

Question

JSONCPP has a writer, but all it seems to do is get info from the parser and then output it into a string or a stream. How do I make it alter or create new objects, arrays, values, strings, et cetera and write them into the file?

Answer 1

#include<json/writer.h>
Code:
Json::Value event;
Json::Value vec(Json::arrayValue);
vec.append(Json::Value(1));
vec.append(Json::Value(2));
vec.append(Json::Value(3));
event["competitors"]["home"]["name"] = "Liverpool";
event["competitors"]["away"]["code"] = 89223;
event["competitors"]["away"]["name"] = "Aston Villa";
event["competitors"]["away"]["code"]=vec;
std::cout << event << std::endl;
Output:
{
"competitors" :
{
"away" :
{
"code" : [ 1, 2, 3 ],
"name" : "Aston Villa"
},
"home" :
{
"name" : "Liverpool"
}
}
}

Answer 2

#include <json.h>
#include <iostream>
#include <fstream>
void main()
{
std::ofstream file_id;
op_file_id.open("file.txt");
Json::Value value_obj;
//populate 'value_obj' with the objects, arrays etc.
Json::StyledWriter styledWriter;
file_id << styledWriter.write(value_obj);
file_id.close();
}

Answer 3

AFAICT, you create objects of type Json::Value, which caters for all the JSON data-types, and pass the result to a Json::Writer (one of its derived types, to be specific), or simply to a stream.
E.g.: to write an array of three integers to a file:
Json::Value vec(Json::arrayValue);
vec.append(Json::Value(1));
vec.append(Json::Value(2));
vec.append(Json::Value(3));
std::cout << vec;

Answer 4

Json::StyledWriter is deprecated, you can use Json::StreamWriterBuilder to write json into files.
Json::Value rootJsonValue;
rootJsonValue["foo"] = "bar";
Json::StreamWriterBuilder builder;
builder["commentStyle"] = "None";
builder["indentation"] = " ";
std::unique_ptr<Json::StreamWriter> writer(builder.newStreamWriter());
std::ofstream outputFileStream("/tmp/test.json");
writer -> write(rootJsonValue, &outputFileStream);
The json will be written into /tmp/test.json.
$ cat /tmp/test.json
{
"foo" : "bar"
}

Answer 5

First, you have to create the desired JSON::Value. You should look at all the constructors (first). To create the necessary hierarchies, see append and the operator[] overloads; there are overloads for both array indices and string keys for objects.
One way to write the JSON value back out is using StyledStreamWriter::write and ofstream.
See cegprakash's answer for how to write it.