卡萨布兰卡传奇继续 - 但我取得了进步 [英] Casablanca saga continues - but i have made progress

问题描述

大家好，我现在已成功从服务器检索JSON，但在尝试迭代数组时在Visual Studio中收到第一次机会异常

Hi all, I now have succeeded in retrieving JSON from the server but receive a "first chance exception" in Visual Studio when trying to iterate over the array

#include "stdafx.h"
#include <winsock2.h>
#include <string> 
#include <time.h>
#include <iostream>

#include <cpprest/http_client.h>
#include <cpprest/filestream.h>
#include <cpprest/json.h>

using namespace utility;                    // Common utilities like string conversions
using namespace web;                        // Common features like URIs.
using namespace web::http;                  // Common HTTP functionality
using namespace web::http::client;          // HTTP client features
using namespace concurrency::streams;       // Asynchronous streams


#pragma comment(lib, "Ws2_32.lib")

// Retrieves a JSON value from an HTTP request.
pplx::task<void> RequestJSONValueAsync(http_request requester)
{
	http_client client(L"http://10.10.1.11:9000/jsonrpc.js"); // my local server

	return client.request(requester).then([](http_response response) -> pplx::task<json::value>
	{
		if (response.status_code() == status_codes::OK)
		{
			json::value jsonValue = response.extract_json().get();
			json::value jsonValue2 = jsonValue.at(U("result"));
		
			// result contains an array ( much bigger but you get the picture)
			//artists_loop [{"artist":"10,000 Maniacs","id":319},{"artist":"Abb
			// ie Lathe","id":596},{"artist":"Adam Harasiewicz","id":321},{"artist":"Adele","id":322}]

			json::value ArtistsValue = jsonValue2.at(U("artists_loop")); // artists_loop is the name of the array in result
	

			if (ArtistsValue.size() > 0)
			{
			// I get a first chance exception here.
				for (auto iter = ArtistsValue.as_object().cbegin(); iter != ArtistsValue.as_object().cend(); ++iter)
				{
					
				}
			}
			
			return response.extract_json();
		}

		// Handle error cases, for now return empty json value... 
		return pplx::task_from_result(json::value());
	})
		.then([](pplx::task<json::value> previousTask)
	{
		try
		{
			const json::value& v = previousTask.get();
			// Perform actions here to process the JSON value...
		}
		catch (const http_exception& e)
		{
			// Print error.
			std::ostringstream ss;
			ss << e.what() << std::endl;
			std::cout << ss.str();
		}
	});
}

int wmain()
{
	http_request requester;
	requester.set_method(methods::POST);
	
	requester.headers().set_content_type(U("application/json"));
	requester.set_body("{\"id\":1,\"method\":\"slim.request\",\"params\":[null,[\"artists\",\"0\",\"-1\"]]}\n");

	RequestJSONValueAsync(requester).wait();
}

抱歉格式化无法让它变得更好。



我尝试过：



查看有关血腥细节的问题

sorry about the formatting couldn't get it any better.

What I have tried:

See question for the gory details

推荐答案

发现这个

Found this

Taking a look at the changelog for version 2.0.0, you'll find this:

Breaking Change - Changed how iteration over json arrays and objects is performed. No longer is an iterator of std::pair returned. Instead there is a separate iterator for arrays and objects on the json::array and json::object class respectively. This allows us to make performance improvements and continue to adjust accordingly. The array iterator returns json::values, and the object iterator now returns std::pair.

因此我将代码更改为此

so I changed my code to this

for (auto &iter = jsonValue2.as_array().cbegin(); iter != jsonValue2.as_array().cend(); ++iter)
				{
					json::value v = iter[0];
					std::wcout << v.at(U("artist")).as_string() << L": " << v.at(U("id")) << std::endl;
					
				}

一切都很好 - 所以异常试图迭代json :: object而不是json :: array

and all is good - so the exception was trying to iterate over a json::object instead of json::array

这篇关于卡萨布兰卡传奇继续 - 但我取得了进步的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！