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How to send data in Json format using service client in c++ code

asked 2017-04-24 07:26:11 -0500

can-43811 gravatar image

updated 2018-07-19 23:17:51 -0500

130s gravatar image

Hi ,

How data send in Json format using service client ROS in c++ code(using srv file).


For example :

{ "op": "subscribe", "topic": "/cmd_vel", "type": "geometry_msgs/Twist" }


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You can put json into a string. Or do you mean make the entire message into json, and use it outside of ros with for example a web server that uses json?

lucasw gravatar image lucasw  ( 2017-04-24 10:56:04 -0500 )edit

yes entire request format should be in json format and same needs to be published so that other node can subscribe the same.

can-43811 gravatar image can-43811  ( 2017-04-24 20:06:00 -0500 )edit

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answered 2017-04-24 11:42:51 -0500

Am not so sure what you want to do, but I can tell you C++ and Json... hummm

you can use a lib called rapid json and generate the json you need appending key-values as it were a dictionary

here an example:

#include <iostream>
#include <string>

#include <rapidjson\document.h>
#include <rapidjson\writer.h>
#include <rapidjson\stringbuffer.h>

void output(const rapidjson::Document& document)

    std::string strOp = document["op"].GetString();
    std::string ret = "{\"op\":\"" + strOp;

    std::string strTopic = document["topic"].GetString();
    ret += "\", \"topic\":\"" + strTopic;

    std::string strType = document["type"].GetString();
    ret += "\", \"type\":\"" + strType + "\"}";

    std::cout << "json" << std::endl;
    std::cout << ret << std::endl;
    //{ "op": "subscribe", "topic" : "/cmd_vel", "type" : "geometry_msgs/Twist" }

int main(int argC, char** argV)
    std::cout << "ROS" << std::endl;
    rapidjson::Document fromScratch;

    rapidjson::Document::AllocatorType& allocator = fromScratch.GetAllocator();

    fromScratch.AddMember("op", "subscribe", allocator);
    fromScratch.AddMember("topic", "/cmd_vel", allocator);
    fromScratch.AddMember("type", "geometry_msgs/Twist", allocator);


    return 0;

The output will look like: image description

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Sure i will form the json string in above format and publish through service client. usually i need 10 this kind of strings . In this case i need to use array of strings.

can-43811 gravatar image can-43811  ( 2017-04-24 20:08:08 -0500 )edit

JSON can represent arrays too, why not do it all in one string?

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2018-07-20 00:51:53 -0500 )edit

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Asked: 2017-04-24 07:26:11 -0500

Seen: 3,669 times

Last updated: Jul 19 '18