Curl HTTP GET and JsonCpp parsing - basic functionality

curl_jsoncpp_example.cpp

#include <cstdint>
#include <iostream>
#include <memory>
#include <string>

#include <curl/curl.h>
#include <json/json.h>

namespace
{
    std::size_t callback(
            const char* in,
            std::size_t size,
            std::size_t num,
            std::string* out)
    {
        const std::size_t totalBytes(size * num);
        out->append(in, totalBytes);
        return totalBytes;
    }
}

int main()
{
    const std::string url("http://date.jsontest.com/");

    CURL* curl = curl_easy_init();

    // Set remote URL.
    curl_easy_setopt(curl, CURLOPT_URL, url.c_str());

    // Don't bother trying IPv6, which would increase DNS resolution time.
    curl_easy_setopt(curl, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);

    // Don't wait forever, time out after 10 seconds.
    curl_easy_setopt(curl, CURLOPT_TIMEOUT, 10);

    // Follow HTTP redirects if necessary.
    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);

    // Response information.
    long httpCode(0);
    std::unique_ptr<std::string> httpData(new std::string());

    // Hook up data handling function.
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, callback);

    // Hook up data container (will be passed as the last parameter to the
    // callback handling function).  Can be any pointer type, since it will
    // internally be passed as a void pointer.
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, httpData.get());

    // Run our HTTP GET command, capture the HTTP response code, and clean up.
    curl_easy_perform(curl);
    curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &httpCode);
    curl_easy_cleanup(curl);

    if (httpCode == 200)
    {
        std::cout << "\nGot successful response from " << url << std::endl;

        // Response looks good - done using Curl now.  Try to parse the results
        // and print them out.
        Json::Value jsonData;
        Json::Reader jsonReader;

        if (jsonReader.parse(*httpData.get(), jsonData))
        {
            std::cout << "Successfully parsed JSON data" << std::endl;
            std::cout << "\nJSON data received:" << std::endl;
            std::cout << jsonData.toStyledString() << std::endl;

            const std::string dateString(jsonData["date"].asString());
            const std::size_t unixTimeMs(
                    jsonData["milliseconds_since_epoch"].asUInt64());
            const std::string timeString(jsonData["time"].asString());

            std::cout << "Natively parsed:" << std::endl;
            std::cout << "\tDate string: " << dateString << std::endl;
            std::cout << "\tUnix timeMs: " << unixTimeMs << std::endl;
            std::cout << "\tTime string: " << timeString << std::endl;
            std::cout << std::endl;
        }
        else
        {
            std::cout << "Could not parse HTTP data as JSON" << std::endl;
            std::cout << "HTTP data was:\n" << *httpData.get() << std::endl;
            return 1;
        }
    }
    else
    {
        std::cout << "Couldn't GET from " << url << " - exiting" << std::endl;
        return 1;
    }

    return 0;
}

output.txt

Got successful response from http://date.jsontest.com/
Successfully parsed JSON data

JSON data received:
{
   "date" : "03-09-2015",
   "milliseconds_since_epoch" : 1425938476314,
   "time" : "10:01:16 PM"
}

Natively parsed:
	Date string: 03-09-2015
	Unix timeMs: 1425938476314
	Time string: 10:01:16 PM

run-command

#!/usr/bin/env bash

g++ curl_jsoncpp_example.cpp -ljsoncpp -lcurl -o example.out && ./example.out

It works! thanks.

This was very helpful, thank you! However int httpCode(0); on line 42 should be long httpCode(0);. If I don't make this change curl_easy_cleanup segfaults on my machine.

From curl/easy.h:

/*
 * NAME curl_easy_getinfo()
 *
 * DESCRIPTION
 *
 * Request internal information from the curl session with this function.  The
 * third argument MUST be a pointer to a long, a pointer to a char * or a
 * pointer to a double (as the documentation describes elsewhere).  The data
 * pointed to will be filled in accordingly and can be relied upon only if the
 * function returns CURLE_OK.  This function is intended to get used *AFTER* a
 * performed transfer, all results from this function are undefined until the
 * transfer is completed.
 */
CURL_EXTERN CURLcode curl_easy_getinfo(CURL *curl, CURLINFO info, ...);

thanks

Thanks @connormanning

This is very useful, although I got the same Segmentation fault on my machine. So thanks to @alandipert's comment figuring out the fix.

Please check for the more generic httpCode instead of just 200. This also allows the code to work with file:// URLs.
if (httpCode != CURLE_HTTP_RETURNED_ERROR)

How do I install the json library?

Provide an example to send JSON request & recive ?

Is there a way to get this working without using deprecated classes? It won't let me build it now as this is several years old, unfortunately.

@Alppuccino please look at this code example
https://github.com/open-source-parsers/jsoncpp/blob/2703c306a3168e15613d94e57fb8832138d9155d/example/readFromStream/readFromStream.cpp#L24
hope it helps you.

How do I install the json library?

I want json Library please

It works! thanks.

Please send json.h Library

what to do if json returned is in array form and contains more then one record?
EDIT:-got it working with this for (Json::Value::ArrayIndex i = 0; i != jsonData.size(); i++)

download jsoncpp-master from this link https://github.com/open-source-parsers/jsoncpp
now you need python to run python .py script named "amalgamate.py" its inside jsoncpp-master after running this script you will see new folder named "dist" copy this folder in your project and now simply add jsoncpp.cpp file in source files and json.h and json-forwards.h files in Header files in your project.
now go to your project properties->c++->general->additional include directories->
here give path "jsoncpp-master\include"
NOTE:- you have to give path where your jsoncpp-master\include is located on your pc.
now at top of your code type #include <json/json.h>
now use json in your code

error C4996: 'Json::Reader': Use CharReader and CharReaderBuilder instead what I can do to fix it ?

error C4996: 'Json::Reader': Use CharReader and CharReaderBuilder instead what I can do to fix it ?

This is because the person that posted this has not updated the code for the latest version.

class JSONCPP_DEPRECATED(
    "Use CharReader and CharReaderBuilder instead.") JSON_API Reader {

So basically replace:

Json::Reader jsonReader;

With:

Json::CharReaderBuilder builder;

Also replace:

std::unique_ptr<std::string> httpData(new std::string()); // why would you even do this!?

With:

std::string httpData;

Complete "fix":

        // Response looks good - done using Curl now.  Try to parse the results
        // and print them out.
        Json::Value jsonData;
        JSONCPP_STRING jsonError;
        Json::CharReaderBuilder builder;

        const std::unique_ptr<Json::CharReader> reader(builder.newCharReader());

        if (reader->parse(httpData.c_str(), httpData.c_str() + httpData.length(), &jsonData, &jsonError))

after using the "fix" httpData.get is not available anymore