Json-cpp - how to initialize from string and get string value?

Json::Reader is deprecated. Use Json::CharReader and Json::CharReaderBuilder instead:

std::string strJson = R"({"foo": "bar"})";

Json::CharReaderBuilder builder;
Json::CharReader* reader = builder.newCharReader();

Json::Value json;
std::string errors;

bool parsingSuccessful = reader->parse(
    strJson.c_str(),
    strJson.c_str() + strJson.size(),
    &json,
    &errors
);
delete reader;

if (!parsingSuccessful) {
    std::cout << "Failed to parse the JSON, errors:" << std::endl;
    std::cout << errors << std::endl;
    return;
}

std::cout << json.get("foo", "default value").asString() << std::endl;

Kudos to p-a-o-l-o for their answer here: Parsing JSON string with jsoncpp

Hello it is pretty simple:

1 - You need a CPP JSON value object (Json::Value) to store your data

2 - Use a Json Reader (Json::Reader) to read a JSON String and parse into a JSON Object

3 - Do your Stuff :)

Here is a simple code to make those steps:

#include <stdio.h>
#include <jsoncpp/json/json.h>
#include <jsoncpp/json/reader.h>
#include <jsoncpp/json/writer.h>
#include <jsoncpp/json/value.h>
#include <string>

int main( int argc, const char* argv[] )
{

    std::string strJson = "{\"mykey\" : \"myvalue\"}"; // need escape the quotes

    Json::Value root;   
    Json::Reader reader;
    bool parsingSuccessful = reader.parse( strJson.c_str(), root );     //parse process
    if ( !parsingSuccessful )
    {
        std::cout  << "Failed to parse"
               << reader.getFormattedErrorMessages();
        return 0;
    }
    std::cout << root.get("mykey", "A Default Value if not exists" ).asString() << std::endl;
    return 0;
}

To compile: g++ YourMainFile.cpp -o main -l jsoncpp

I hope it helps ;)