libcurl在write_data(）函数处爆炸

如果curl查询满足验证要求，我将尝试将其内容写入文件。我的代码编译没有错误，但在执行时我收到以下错误->

cryptsy # ./foundGetPrice2.o|wgetpaste
foundGetPrice2.o: rapidjson/include/rapidjson/document.h:911: rapidjson::GenericValue<Encoding, Allocator>::MemberIterator rapidjson::GenericValue<Encoding, Allocator>::FindMember(const rapidjson::GenericValue<Encoding, SourceAllocator>&) [with SourceAllocator = rapidjson::MemoryPoolAllocator<>; Encoding = rapidjson::UTF8<>; Allocator = rapidjson::MemoryPoolAllocator<>; rapidjson::GenericValue<Encoding, Allocator>::MemberIterator = rapidjson::GenericMemberIterator<false, rapidjson::UTF8<>, rapidjson::MemoryPoolAllocator<> >]: Assertion `IsObject()' failed.
Your paste can be seen here: https://bpaste.net/show/768ea25c86d5

在我的代码的第42行，您可能会注意到curl的2行写操作被注释掉了。如果我从那里写_data（），它是有效的，但没有验证，所以它对我没有好处。

#include "rapidjson/include/rapidjson/document.h"
#include "rapidjson/include/rapidjson/rapidjson.h"
#include "rapidjson/include/rapidjson/writer.h"
#include <cstdio>
#include <iostream>
#include <fstream>
#include <stdio.h>
#include <curl/curl.h>
#include <unistd.h>
using namespace rapidjson;
struct myData
{
        std::fstream *file;
        std::string *str;
};
size_t write_data(void *ptr, size_t size, size_t nmemb, myData *data)
{
        size_t numBytes = size * nmemb;
        if (data->file)
                data->file->write((char*)ptr, numBytes);
        if (data->str)
                *data->str += std::string((char*)ptr, numBytes);
        return numBytes;
}
std::string tradeData;
int getData()
{
        int count = 0;
        //begin non terminating loop
        while(true)
        {
                count++;
                CURL *curl = curl_easy_init();
                if (curl)
                {
                        curl_easy_setopt(curl, CURLOPT_URL, "http://pubapi.cryptsy.com/api.php?method=singlemarketdata&marketid=155");
                        std::fstream file("myfile.txt", std::ios_base::out | std::ios_base::ate);
                        std::string json;
                        myData data;
                        data.file = &file;
                        data.str = &json;
                        //curl_easy_setopt(curl, CURLOPT_WRITEDATA, &data);
                        //curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &write_data);
                        CURLcode res = curl_easy_perform(curl);
                        if (res != CURLE_OK)
                        {
                                std::cerr << "curl_easy_perform() failed: " << curl_easy_strerror(res) << std::endl;
                        }
                        else
                        {
                                file << std::endl;
                                Document document;
                                document.Parse(json.c_str());
                                std::string tradeUpdate = document["return"]["markets"]["DRK"]["lasttradeprice"].GetString();
                                if (tradeUpdate > tradeData){
                                        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &data);
                                        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &write_data);
                                        std::cout << std::endl;
                                }
                                else{
                                        std::cout << "There was an error! " << tradeData << std::endl;
                                }
                        }
                        /* always cleanup */
                        curl_easy_cleanup(curl);
                }
                usleep(10000000);
        }
        return 0;
}
//Le Main
int main(void)
{
        getData();
}

gdb输出：

gdb-bt输出的bpaste

如何在验证后正确写入来自libcURL请求的数据？