使用libCurl和JsonCpp从https webserver进行解析

Question

所以我一直在互联网上寻找使用libcurl和jsoncpp解析JSON的基本示例,但我找不到一个.

有人可以指出我正确的方向或指定这里,一个使用libcurl和jsoncpp的简单例子,从指定的网页下载json(链接本身以.json结尾所以它将直接拉json)解析并打印它.

所有帮助表示赞赏.谢谢!

Euden

Answer 1

这是一个自包含的例子:a)HTTP通过libcurl获取JSON对象,然后b)用JsonCpp解析它.@WhozCraig说这是两个完全独立的活动是正确的,但我碰巧有一个项目同时执行这两个操作,因此我汇总了这个从这个漂亮的页面获取和解析JSON的小样本.

如果将此代码放在一个名为的文件中main.cpp,那么您可以编译,链接和运行(假设您的路径上有libcurl和libjsoncpp):

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

// main.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.
    int 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, 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;
}

输出如下:

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