从基于迭代器的 for 循环转换后，如何在 map::find() 中调用方法？

Question

I would like to convert my existing for-loop map to use map.find().

As seen below the WeatherTree.search checks against the year variable but WeatherMap also checks against the same year variable.

The below portion of the map is found in Menu.cpp.

    if(WeatherTree.search(year))
    {
        for (itr = WeatherMap.begin(); itr != WeatherMap.end(); itr++)
        {
            if(itr->first == year)
            {
                for(auto itr2 = itr->second.begin(); itr2 != itr->second.end(); itr2++)
                {
                    if(itr2->GetMonth() == month)
                    {
                        wind += itr2->GetWind();
                        temperature += itr2->GetTemperature();
                        count++;
                    }
                }
            }
        }
    }

What I would like to do instead is WeatherTree.search continue to check against year variable while WeatherMap using find() check against month. WeatherTree is a binary search tree (BST) but it is not important as my question is about STL map. The WeatherMap is also index using month rather than year.

But how do I call the GetWind() and GetTemperature() and also what about the count which will be use for calculating average later.

I have Google they mostly return what the cpp documentation is showing which is not I wanted.

WeatherMap[W.GetMonth()].insert(W);

if(WeatherTree.search(year))
{
    auto itr = WeatherMap.find(month);
    if (itr != WeatherMap.end())
    {
        wind +=
        temperature +=
        count++;
    }
}

Menu.cpp

#include "Menu.h"

using namespace std;

Menu::Menu()
{
    Load();
}

void Menu::Load()
{
    ifstream ifile;
    string filename, line, smonth, syear, swind, stemperature, shumidity;
    cout << "Enter the filename to open" << endl;
    getline(cin, filename);
    ifile.open(filename);
    if (!ifile.is_open())
    {
        cout << "Please try again!" << endl;
        system("PAUSE");
        exit(EXIT_FAILURE);
    }
    else
    {
        getline(ifile, line);
        while (getline(ifile, line))
        {
            if (!line.empty())
            {
                istringstream istream(line);
                getline(istream, smonth, ',');
                getline(istream, syear ',');
                getline(istream, swind, ',');
                getline(istream, shumidity, ',');
                getline(istream, stemperature, '\n');

                int month = stoi(smonth);
                int year = stoi(syear);
                double wind = stod(swind);
                int humidity = stoi(shumidity);
                double temperature = stod(stemperature);

                Weather W;
                W.SetWeather(month, year, wind, humidity, temperature);
                WeatherMap[W.GetYear()].insert(W);
                WeatherTree.insert(W.GetYear());
            }
        }
        ifile.close();
    }
}

void Menu::Options()
{
    int options = 0;

    while(options != 3)
    {
        cout << "1) Average wind speed and temperature of a month and year" << endl;
        cout << "2) Average humidity of a year" << endl;
        cout << "3) Quit" << endl;
        cin >> options;

        switch(options)
        {
            case 1:
                FirstOption();
                break;
            case 2:
                SecondOption();
                break;
            case 3:
                cout << "Goodbye!" << endl;
                break;
            default:
                cout << "Invalid input" << endl;
                break;
        }
    }
}

void Menu::FirstOption()
{
    int month = 0;
    int year = 0;
    int count = 0;
    double wind = 0.0;
    double temperature = 0.0;
    Weather W2;
    map<int, set<Weather>>::iterator itr;

    cout << "Enter month" << endl;
    cin >> month;
    cout << "Enter year" << endl;
    cin >> year;

    if(WeatherTree.search(year))
    {
        for (itr = WeatherMap.begin(); itr != WeatherMap.end(); itr++)
        {
            if(itr->first == year)
            {
                for(auto itr2 = itr->second.begin(); itr2 != itr->second.end(); itr2++)
                {
                    if(itr2->GetMonth() == month)
                    {
                        wind += itr2->GetWind();
                        temperature += itr2->GetTemperature();
                        count++;
                    }
                }
            }
        }
    }

    if (wind != 0 || temperature != 0 || wind < 0 || temperature < 0)
    {
        cout << W2.GetAvg(wind, count) << "km/h" << W2.GetAvg(temperature, count) << "degree celsius" << endl;
    }
    else
    {
        cout << "No information" << endl;
    }
}

Weather.cpp

#include "Weather.h"

using namespace std;

Weather::Weather()
{
    wind = 0;
    humidity = 0;
    temperature = 0;
}

int Weather::GetMonth()
{
    return month;
}

int Weather::GetYear()
{
    return year;
}

double Weather::GetWind()
{
    return wind;
}

int Weather::GetHumidity()
{
    return humidity;
}

double Weather::GetTemperature()
{
    return temperature;
}

void Weather::SetMonth(int m)
{
    month = m;
}

void Weather::SetYear(int y)
{
    year = y;
}

void Weather::SetWind(double w)
{
    wind = w;
}

void Weather::SetHumidity(int h)
{
    humidity = h;
}

void Weather::SetTemperature(double t)
{
    temperature = t;
}

void Weather::SetWeather(int m, int y, double w, int h, double t)
{
    month = m;
    year = y;
    wind = w;
    humidity = h;
    temperature = t;
}

double Weather::GetAvg(double total, int count)
{
    return total / count;
}

Answer 1

First your should know map::find() works by comparing keys of the map to a given query. So you can't using find() to compare months since month is not the key of you map.

Note: Possibly you don't need WeatherTree since you are using year as a key saving Weather records.

What you can do:

Method 1:

Keep your current map definition not changed. And iterate in the corresponding Weather set once you are sure the year exists.

    if(WeatherMap.find(year) != WeatherMap.end())
    {
        for (auto itr = WeatherMap[year].begin(); itr != WeatherMap[year].end(); itr++)
        {
           if(itr->GetMonth() == month)
           {
               wind += itr->GetWind();
               temperature += itr->GetTemperature();
               count++;
            }
        }
    }

Method 2

Change your map to map<<int, int>, W> , ie, using both year and month as a key. Then you have:

     if (WeatherMap.find(make_pair(year, month)) != WeatherMap.end()) {
         // calculate
     }

Answer 2

There is a while that I do not program in C++, but this could be a solution (I did not test it):

std::for_each(WeatherMap.begin(), WeatherMap.end(), [&](const auto& value) {
    if ( value.first == year ) {
        auto it1 = value.second.begin();
        while( (it1 = std::find_if(it1, value.second.end(), [&](const auto& item) {
                if ( item.GetMonth() == month ) {
                    ...
                    return true;
                }
                return false;
                })) != value.second.end()
              )
              it1++;
    }
}