Iterating through objects in JsonCpp

Question

I have a C++ application that uses jsoncpp to decode a JSON string. I have created the following function but it only shows me the top level objects...

How do I get

Answer 1

If you are just looking to print out the Json::Value, there's a method for that:

Json::Value val;
/*...build the value...*/
cout << val.toStyledString() << endl;

Also, you may want to look into the Json::StyledWriter, the documentation for it is here. I believe it print a human friendly version. Also, Json::FastWriter, documentation here, prints a more compact form.

Answer 2

You have some errors related to seemingly not having a great handle on recursion or the key->value nature of JSON and how that relates to the library you're using. I haven't tested this code at all, but it should work better.

void CDriverConfigurator::PrintJSONValue( const Json::Value &val )
{
    if( val.isString() ) {
        printf( "string(%s)", val.asString().c_str() ); 
    } else if( val.isBool() ) {
        printf( "bool(%d)", val.asBool() ); 
    } else if( val.isInt() ) {
        printf( "int(%d)", val.asInt() ); 
    } else if( val.isUInt() ) {
        printf( "uint(%u)", val.asUInt() ); 
    } else if( val.isDouble() ) {
        printf( "double(%f)", val.asDouble() ); 
    }
    else 
    {
        printf( "unknown type=[%d]", val.type() ); 
    }
}

bool CDriverConfigurator::PrintJSONTree( const Json::Value &root, unsigned short depth /* = 0 */) 
{
    depth += 1;
    printf( " {type=[%d], size=%d}", root.type(), root.size() ); 

    if( root.size() > 0 ) {
        printf("\n");
        for( Json::Value::const_iterator itr = root.begin() ; itr != root.end() ; itr++ ) {
            // Print depth. 
            for( int tab = 0 ; tab < depth; tab++) {
               printf("-"); 
            }
            printf(" subvalue(");
            PrintJSONValue(itr.key());
            printf(") -");
            PrintJSONTree( *itr, depth); 
        }
        return true;
    } else {
        printf(" ");
        PrintJSONValue(root);
        printf( "\n" ); 
    }
    return true;
}

Answer 3

This is a good example that can print either json objects and object member (and it's value) :

Json::Value root;               // Json root
Json::Reader parser;            // Json parser

// Json content
string strCarPrices ="{ \"Car Prices\": [{\"Aventador\":\"$393,695\", \"BMW\":\"$40,250\",\"Porsche\":\"$59,000\",\"Koenigsegg Agera\":\"$2.1 Million\"}]}";

// Parse the json
bool bIsParsed = parser.parse( strCarPrices, root );
if (bIsParsed == true)
{
    // Get the values
    const Json::Value values = root["Car Prices"];

    // Print the objects
    for ( int i = 0; i < values.size(); i++ )
    {
        // Print the values
        cout << values[i] << endl;

        // Print the member names and values individually of an object
        for(int j = 0; j < values[i].getMemberNames().size(); j++)
        {
            // Member name and value
            cout << values[i].getMemberNames()[j] << ": " << values[i][values[i].getMemberNames()[j]].asString() << endl;
        }
    }
}
else
{
    cout << "Cannot parse the json content!" << endl;
}

The output :

{
        "Aventador" : "$393,695",
        "BMW" : "$40,250",
        "Koenigsegg Agera" : "$2.1 Million",
        "Porsche" : "$59,000"
}
Aventador: $393,695
BMW: $40,250
Koenigsegg Agera: $2.1 Million
Porsche: $59,000

Answer 4

Given member names, get the values

// Print all items under data1 value
vector<string> memberNames = root["test1"]["data1"].getMemberNames();
for (const string& mn : memberNames)
{
    cout << "[" << mn << "]:" << "[" << root["test1"]["data1"].get(mn, "None") << "]" << endl;
}

Answer 5

There is an easy way to iterate over all fields in json::value. I omitted the printf stuff.

#include "cpprest/json.h"
#include "cpprest/filestream.h"

using web::json::value;
using std::wstring;

static void printOneValue(const wstring &key, const double &value);
static void printOneValue(const wstring &key, const bool &value);
static void printOneValue(const wstring &key, const int &value);
static void printOneValue(const wstring &key, const wstring &value);
static void printOne(const wstring &key, const value &v, _num level);
static void printTree(const value &v);

static void printTree(const value &v)
{
    if(!v.is_object())
        return;

    try
    {
        printOne(wstring(), v, 0);
    }
    catch(...)
    {
        // error handling
    }
}

static void printOne(const wstring &key, const value &v, _num level)
{
    switch(v.type())
    {
    case value::value_type::Number:
        if(v.is_double())
            printOneValue(key, v.as_double());
        else
            printOneValue(key, v.as_integer());
        break;
    case value::value_type::Boolean:
        printOneValue(key, v.as_bool());
        break;
    case value::value_type::String:
        printOneValue(key, v.as_string());
        break;
    case value::value_type::Object:
        for(auto iter : v.as_object())
        {
            const wstring &k = iter.first;
            const value &val = iter.second;
            printOne(k, val, level+1);
        }
        break;
    case value::value_type::Array:
        for(auto it : v.as_array())
        {
            printOne(key, it, level+1);
        }
        break;
    case value::value_type::Null:
    default:
        break;
    }
}

static void printOneValue(const wstring &key, const wstring &value)
{
    // process your key and value
}

static void printOneValue(const wstring &key, const int &value)
{
    // process your key and value
}

static void printOneValue(const wstring &key, const double &value)
{
    // process your key and value
}

static void printOneValue(const wstring &key, const bool &value)
{
    // process your key and value
}