Create Json Message using JsonCpp

Question

I'm trying to create a Json message using Jsoncpp. I've done as follows:

#include <string>
#include <iostream>
#include <sstream>    
#include <json/json.h>

int main()
{
  std::string Value = "5.17e9";
  std::string Type = "TX";
  std::string Parameter = "Frequency";

  Json::Value root; 
  root.append("Type");
  root.append("Parameter");
  root.append("Value");
  root["Type"] = Type;
  root["Parameter"] = Parameter;
  root["Value"] = Value; 

  Json::FastWriter fastwriter;
  std::string message = fastwriter.write(root);
  std::cout<<message<<std::endl;

  return 0;
 }

compiling this code using the following command line:

g++ -o clients clients.cpp -ljsoncpp -lzmq

This Kind of error occurs:

clients.cpp:(.text._ZN20multi_usrp_emulation7client1Ev[_ZN20multi_usrp_emulation7client1Ev    ]+0x1d9): undefined reference to `Json::Value::operator=(Json::Value)'
clients.cpp:(.text._ZN20multi_usrp_emulation7client1Ev[_ZN20multi_usrp_emulation7client1Ev    ]+0x224): undefined reference to `Json::Value::operator=(Json::Value)'
clients.cpp:(.text._ZN20multi_usrp_emulation7client1Ev[_ZN20multi_usrp_emulation7client1Ev    ]+0x26c): undefined reference to `Json::Value::operator=(Json::Value)'
collect2: error: ld returned 1 exit status

What is wrong with my code?

What version of jsoncpp are you using? Perhaps it is related to this issue: github.com/open-source-parsers/jsoncpp/issues/484 ? — Martin Hollstein
– Martin Hollstein, Commented Jun 13, 2016 at 13:47
I don't how to check the version. But I've downloaded today via github. I read the question that you attached but I didn't understand it well..can you help me? — Felice Di Stolfa
– Felice Di Stolfa, Commented Jun 13, 2016 at 14:10

Kenny Ostrom · Accepted Answer · 2016-06-13 14:38:36Z

4

I'm not sure about the link error, but there is a problem with the code that might be handled differently in your compiler. It's a runtime error for me.

Json::Value root; 
root.append("Type"); // makes root into arrayValue
root["Type"] = Type; // accesses root as an objectValue
// triggers assert in Json::Value::resolveReference

this is how I do it:

Json::Value root; 
root["Type"] = Type;

answered Jun 13, 2016 at 14:38

Kenny Ostrom

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