Jsoncpp problems - c++

Question

I am using Jsoncpp to parse json-formats for c++.
I do not understand how it works though; there is a lack of documentation and examples to get me started, and I was wondering if anyone could give me some quick pointers. The only examples I've found deals with files...
I'm using a HTTP stack to get a json-message in a buffer. For example, a buffer contains the message {"state":"Running"}. How do I use the Json::reader to parse this? Again the only example I've found deals with reading from files
How do you write values to a Json-message? For example I want to write "monkey : no" and "running : yes" to a Json-message which I can then use in my GET request.
Thanks
UPDATE:
on 1), for example, how to parse a buffer containing a json-message like this:
char* buff;
uint32_t buff_size;

Answer 1

Maybe this is good sample for first part of your question:
Json::Value values;
Json::Reader reader;
reader.parse(input, values);
Json::Value s = values.get("state","default value");

Answer 2

There is anything but lack of documentation. Yes, it's mainly reference documentation, but it's quite good and well cross-linked.
Just read the documentation
Just use this class or possibly use the other class

Answer 3

Sample code for your reference, below:
file.json
{
"B":"b_val2",
"A":{
"AA":"aa_val1",
"AAA" : "aaa_val2",
"AAAA" : "aaaa_val3"
},
"C":"c_val3",
"D":"d_val4"
}
jsoncpp usage scenario as below, for above sample json file.
#include <iostream>
#include "json/json.h"
#include <fstream>
using namespace std;
int main(){
Json::Value root;
Json::Reader reader;
const Json::Value defValue; //used for default reference
std::ifstream ifile("file.json");
bool isJsonOK = ( ifile != NULL && reader.parse(ifile, root) );
if(isJsonOK){
const Json::Value s = root.get("A",defValue);
if(s.isObject()){
Json::Value s2 = s.get("AAA","");
cout << "s2 : " << s2.asString() << endl;
}else{
cout << "value for key \"A\" is not object type !" << endl;
}
}
else
cout << "json not OK !!" << endl;
return 1;
}
Output::
s2 : aaa_val2
Additionally, I have used the "amalgamate.py" for generating and using the jsoncpp for the sample source above.