遍历 objects 的列表

Question

我试图遍历包含 object 的列表。我正在使用天气 API 读取数据并将每个数据成员存储在 object 中，然后将每个 object 存储在列表中。存储整个列表后，我希望能够遍历列表并显示 objects。我正在以 Json 的形式读取数据，并且我正在使用 casablanca 包来这样做。我想要做的就是能够在 main.cpp 的 displayFullForcast 函数中循环遍历我的列表。这是我的列表定义：

list<Weather> weather;

这是我的 header:

    #pragma once

    #include<string>
    #include<iostream>
    #include <list>
    using std::list;
    using std::string;

    //const static int MAX_DAYS = 5;

    class Weather
    {
        public:
            Weather();
            ~Weather();
            Weather(double currentTemperature, double maxTemperature,
                double minTemperature, string weatherDescription,double humidity, string time);
            list<Weather> weather;
        private:
            string cityState;
            double currentTemperature;
            double highTemperature;
            double lowTemperature;
            string weatherDescription;
            double humidity;
            double highestTemperature;
            double lowestTemperature;
            string time;
    };

这是我的实现：

#include "Weather.h"
#include <list>
#include <string>
#include <iostream>

using std::cout;
using std::endl;
using std::cin;


Weather::Weather(double currentTemperature, double maxTemperature, double minTemperature,
    string weatherDescription, double humidity, string time) :
    cityState(cityState), currentTemperature(currentTemperature), highTemperature(highTemperature), lowTemperature(lowTemperature),
    weatherDescription(weatherDescription), humidity(humidity), time(time)
{
}
Weather::Weather()
{
    cityState = "";
    currentTemperature = 0.0;
    highTemperature = 0.0;
    lowTemperature = 0.0;
    weatherDescription = "";
    humidity = 0.0;
    highestTemperature = 0.0;
    lowestTemperature = 0.0;

}

Weather::~Weather()
{

}

这是我的 main.cpp

void displayFullForcast()
{
    list<Weather>weather;
    for (list<Weather>::iterator it = weather.begin(); it != weather.end(); ++it)
    {
        cout << *it << endl;
    }

}

void displayTodayForcast()
{
    list<Weather>weather;
}

void displayLowHigh()
{
    list<Weather>weather;
}

void displayHumidity()
{
    list<Weather>weather;
}


void displayMenu()
{
    int choice = 0;
    cout << "What option would you like to see:\n"
        << "(1) Forcast for 5 days\n"
        << "(2) Forcast for Today\n"
        << "(3) The Lowest and Highest Temperature\n"
        << "(4) Humidity for Today\n" << endl;
    cin >> choice;
    switch (choice)
            {
            case 1: displayFullForcast();
                break;
            case 2: displayTodayForcast();
                break;
            case 3: displayLowHigh();
                break;
            case 4: displayHumidity();
                break;
            }
}



void executeWeatherQuery()
{
    http_client client(U("http://api.openweathermap.org"));
    uri_builder builder(U("/data/2.5/forecast"));
    builder.append_query(U("q"), U("Searcy,AR"));
    builder.append_query(U("appid"), U("5ee41aef99a6e283abcdd5a04d89ae67"));
    builder.append_query(U("units"), U("imperial"));
    builder.append_query(U("mode"), U("json"));

    http_response response = client.request(methods::GET, builder.to_string()).get();
    web::json::value forecastJson = response.extract_json(true).get();
    web::json::value forecastListJson = forecastJson.at(U("list"));

    if (forecastListJson.is_array())
    {
        for (size_t i = 0; i < forecastListJson.size(); i++)
        {
            web::json::value forecastDayJson = forecastListJson[i];
            web::json::value mainJson = forecastDayJson.at(U("main"));
            web::json::value currentTemperatureJson = mainJson.at(U("temp"));
            double currentTemperature = 0;
            if (!currentTemperatureJson.is_null())
            {
                currentTemperature = currentTemperatureJson.as_double();
            }
            cout << "Current Temperature " << currentTemperature << endl;

            web::json::value weatherJson = forecastDayJson.at(U("weather"))[0];
            web::json::value mainWeatherJson = weatherJson.at(U("main"));
            string weatherDescription = "";
            if (!mainWeatherJson.is_null())
            {
                weatherDescription = conversions::to_utf8string(mainWeatherJson.as_string());
            }
            cout << "Weather Description " << conversions::to_utf8string(weatherDescription) << endl;

            web::json::value MainJson = forecastDayJson.at(U("main"));
            web::json::value minTemperatureJson = MainJson.at(U("temp"));
            double minTemperature = 0;
            if (!minTemperatureJson.is_null())
            {
                minTemperature = minTemperatureJson.as_double();
            }
            cout << "Min Temp: " << minTemperature << endl;

            web::json::value MainMaxJson = forecastDayJson.at(U("main"));
            web::json::value maxTemperatureJson = MainMaxJson.at(U("temp"));
            double maxTemperature = 0;
            if (!maxTemperatureJson.is_null())
            {
                maxTemperature = maxTemperatureJson.as_double();
            }
            cout << "Max " << maxTemperature << endl;

            web::json::value MainHumidityJson = forecastDayJson.at(U("main"));
            web::json::value humidityJson = MainHumidityJson.at(U("humidity"));

            double humidity = 0;
            if (!MainHumidityJson.is_null())
            {
                humidity = humidityJson.as_double();
            }
            cout << "Humidity: " << humidity << endl;

            web::json::value MainTimeJson = forecastDayJson.at(U("dt_txt"));
            string time = "";
            if (!MainTimeJson.is_null())
            {
                time = conversions::to_utf8string(MainTimeJson.as_string());

                //time = localtime(time);
            }
            cout << "Time" << time << endl;

            Weather WeatherForcast(currentTemperature, maxTemperature, minTemperature,
                weatherDescription, humidity, time);
            list<Weather>weather;
            weather.push_back(WeatherForcast);
        }
    }
}

void main()
{
    /*string location;
    cout << "Please enter a city and a State (Example: Searcy,AR)" << endl;
    cin >> location;*/
    executeWeatherQuery();


displayMenu();
}

** 我仍然在 cout << *it << endl 线上收到此错误；错误：没有运算符“<<”匹配这些操作数。操作数类型是 std::ofstream 和天气。

Answer 1

您的问题似乎是在您的每个函数中都有一个单独的本地天气列表。

因此您将数据收集到一个列表中，该列表在函数结束时被破坏，然后显示刚刚创建的另一个列表的内容（并且是空的）。

取而代之的是一个全局列表天气。

Answer 2

我没有安装特定天气 API 包，但从您的代码来看，您似乎只是遇到了范围界定问题。

在您的 executeWeatherQuery 中，您声明一个 list<Weather> weather; 然后执行 weather.push_back(WeatherForcast);；该 weather 对象仅对 executeWeatherQuery 函数而言是本地的，因此一旦该函数结束，该 weather 对象就会超出范围并且其中的数据将不再有效。此外，您的其他功能 display 列表，都创建自己的本地 list<Weather> weather;.

相反，请尝试使用全局 list<Weather> weather 作为操作依据。这是带有静态本地（全球）天气对象的主要代码：

static list<Weather> weather;

void displayFullForcast()
{
    for (list<Weather>::iterator it = weather.begin(); it != weather.end(); ++it)
    {
        cout << *it << endl;
    }
}

void displayTodayForcast()
{
}

void displayLowHigh()
{
}

void displayHumidity()
{
}


void displayMenu()
{
    int choice = 0;
    cout << "What option would you like to see:\n"
        << "(1) Forcast for 5 days\n"
        << "(2) Forcast for Today\n"
        << "(3) The Lowest and Highest Temperature\n"
        << "(4) Humidity for Today\n" << endl;
    cin >> choice;
    switch (choice)
            {
            case 1: displayFullForcast();
                break;
            case 2: displayTodayForcast();
                break;
            case 3: displayLowHigh();
                break;
            case 4: displayHumidity();
                break;
            }
}



void executeWeatherQuery()
{
    http_client client(U("http://api.openweathermap.org"));
    uri_builder builder(U("/data/2.5/forecast"));
    builder.append_query(U("q"), U("Searcy,AR"));
    builder.append_query(U("appid"), U("5ee41aef99a6e283abcdd5a04d89ae67"));
    builder.append_query(U("units"), U("imperial"));
    builder.append_query(U("mode"), U("json"));

    http_response response = client.request(methods::GET, builder.to_string()).get();
    web::json::value forecastJson = response.extract_json(true).get();
    web::json::value forecastListJson = forecastJson.at(U("list"));

    if (forecastListJson.is_array())
    {
        for (size_t i = 0; i < forecastListJson.size(); i++)
        {
            web::json::value forecastDayJson = forecastListJson[i];
            web::json::value mainJson = forecastDayJson.at(U("main"));
            web::json::value currentTemperatureJson = mainJson.at(U("temp"));
            double currentTemperature = 0;
            if (!currentTemperatureJson.is_null())
            {
                currentTemperature = currentTemperatureJson.as_double();
            }
            cout << "Current Temperature " << currentTemperature << endl;

            web::json::value weatherJson = forecastDayJson.at(U("weather"))[0];
            web::json::value mainWeatherJson = weatherJson.at(U("main"));
            string weatherDescription = "";
            if (!mainWeatherJson.is_null())
            {
                weatherDescription = conversions::to_utf8string(mainWeatherJson.as_string());
            }
            cout << "Weather Description " << conversions::to_utf8string(weatherDescription) << endl;

            web::json::value MainJson = forecastDayJson.at(U("main"));
            web::json::value minTemperatureJson = MainJson.at(U("temp"));
            double minTemperature = 0;
            if (!minTemperatureJson.is_null())
            {
                minTemperature = minTemperatureJson.as_double();
            }
            cout << "Min Temp: " << minTemperature << endl;

            web::json::value MainMaxJson = forecastDayJson.at(U("main"));
            web::json::value maxTemperatureJson = MainMaxJson.at(U("temp"));
            double maxTemperature = 0;
            if (!maxTemperatureJson.is_null())
            {
                maxTemperature = maxTemperatureJson.as_double();
            }
            cout << "Max " << maxTemperature << endl;

            web::json::value MainHumidityJson = forecastDayJson.at(U("main"));
            web::json::value humidityJson = MainHumidityJson.at(U("humidity"));

            double humidity = 0;
            if (!MainHumidityJson.is_null())
            {
                humidity = humidityJson.as_double();
            }
            cout << "Humidity: " << humidity << endl;

            web::json::value MainTimeJson = forecastDayJson.at(U("dt_txt"));
            string time = "";
            if (!MainTimeJson.is_null())
            {
                time = conversions::to_utf8string(MainTimeJson.as_string());

                //time = localtime(time);
            }
            cout << "Time" << time << endl;

            Weather WeatherForcast(currentTemperature, maxTemperature, minTemperature,
                weatherDescription, humidity, time);
            weather.push_back(WeatherForcast);
        }
    }
}

void main()
{
    /*string location;
    cout << "Please enter a city and a State (Example: Searcy,AR)" << endl;
    cin >> location;*/
    executeWeatherQuery();
    displayMenu();
}

请注意在文件范围内只有一个 weather 对象，而不是每个函数一个 weather 对象。

希望能帮到你。

Answer 3

除了其他人提到的作用域问题，您还需要编写一个函数来打印对象：

std::ostream& operator <<(std::ostream& str, const Weather & w)
{
    str << "Temp will be " << w.temp << std::endl;
}

您还需要将此函数设为 class 的好友。

（写在phone上。欢迎编辑完成功能。）

遍历 objects 的列表

Looping through a list of objects

c++

json

casablanca