如何在不使用复制功能的情况下对具有存储在向量中的日/月/年的实例进行排序

Question

I'm in an intro C++ class and we were tasked with creating a program to take data from a file regarding the weather, input it into an array, then sort it in descending order (where the most recent data is in the array's first index), and output it.

I can get my sort function to work for the years, but once the year is the same and you're sorting by month is where I'm having trouble. And to add even more fuss, we haven't learned the sort() function yet so we are not allowed to use it in the code.

I've attached what I have so far, but be warned it's pretty sloppy and not commented. This is because it's to be submitted online in chunks of code, where sometimes the rest of a bit of code is written for us. I've done my best to piece it together, but some things may not make sense/be out of order. My sortData function is at the bottom, and I've got my most recent attempt at a solution still in there. It doesn't work, obviously, but maybe it'll lend to how I'm trying to go about this.

Any help is greatly appreciated!

#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
#include <vector>
#include <iomanip>

using namespace std;

struct WeatherData {
   int day;
   int month;
   int year;
   int clouds;
   double temp;
   double wind;
   string watch;
};

class WeatherStation {
private:
    vector<WeatherData> m_data;
public:
    WeatherStation();
    int getNumData();
    WeatherData getData(int);
    void sortData();
    void addData(const WeatherData&);
};

int main() {
   string line;
   string file_name;

   cin >> file_name;

   //Weather variables
   int day, month, year, clouds;
   double wind, temp;
   string watch;

   WeatherStation station;
   istringstream sin;
   ifstream fin;
   string watchLine;

   fin.open(file_name.c_str());

    if(fin.fail()) {
        cout << "Could not open file.\n";
        return 1;
    }

    while(getline(fin, line)) {
        sin.clear();
        sin.str(line);
        sin >> day >> month >> year >> clouds >> temp >> wind >> watch;
        getline(sin, watchLine);
        watch = watch + watchLine;

        WeatherData data;
        data.day = day;
        data.month = month;
        data.year = year;
        data.clouds = clouds;
        data.temp = temp;
        data.wind = wind;
        data.watch = watch;

        station.addData(data);
    }

    station.sortData();

    int i;
    for(i = 0; i < getNumData(); i++) {
        cout << "Weather data for " << station.getData(i).month << "/";
        cout << station.getData(i).day << "/";
        cout << station.getData(i).year << ": ";
        cout << "Temp: " << fixed << showpoint << setprecision(2) << station.getData(i).temp;
        cout << ", Wind: " << fixed << showpoint << setprecision(3) << station.getData(i).wind;
        cout << ", Clouds: " << station.getData(i).clouds;
        cout << "\nNotes: " << setw(28) << right << station.getData(i).watch << "\n\n";
    }

    return 0;
}

int WeatherStation::getNumData() {
    return m_data.size();
}

WeatherData WeatherStation::getData(int index) {
    return m_data[index];
}

void WeatherStation::addData(const WeatherData& data) {
    m_data.push_back(data);
}

void WeatherStation::sortData() {
    int i, j, k, l, firstYear, firstMonth;
    WeatherData tempData;
    for(i = 0; i < m_data.size(); i++) {
        firstYear = i;
        for(j = i + 1; j < m_data.size(); j++) {
            if(m_data[j].year > m_data[firstYear].year) {
                firstYear = j;
            }
            else if(m_data[j].year == m_data[firstYear].year) {

                for(k = 0; k < m_data.size(); k++) {
                    firstMonth = k;
                    for(l = k + 1; l < m_data.size(); l++) {
                        if(m_data[l].month > m_data[firstMonth].month) {
                            firstMonth = l;
                        }
                    }
                }

            }
        }
        if(firstYear != i) {
            tempData = m_data[i];
            m_data[i] = m_data[firstYear];
            m_data[firstYear] = tempData;
        }
        else if(firstMonth != k) {
            tempData = m_data[k];
            m_data[k] = m_data[firstMonth];
            m_data[firstMonth] = tempData;
        }
    }
}

Answer 1

If you change your variable name from firstYear to latestDate you might find it clearer. firstYear makes you think you only have a year to work with, but you have the entire WeatherData structure to work with instead.

You don't need a third inner loop (your k loop in your current code) - you can compare the year, month, and day for each item as you check it.

So you can do

if(m_data[j].year > m_data[latestDate].year) {
    latestDate = j;
}
else if(m_data[j].year == m_data[latestDate].year) {
    if(m_data[j].month> m_data[latestDate].month) {
        latestDate = j;
    }
    else if(m_data[j].month == m_data[latestDate].month) {
        ... do the same for day

Ideally you would encapsulate this in a member function of WeatherData or even as a standalone compare function which takes two WeatherData objects, but you can leave it in the sort method if that is what is required by the task.