堆栈内存溢出
  繁体   English   中英

多图的迭代器值不变 - C++

[英]Iterator value for multimap not changing - C++

 原文  2020-06-09 08:32:17  1   1    c++/ class/ iterator/ maps

问题描述

我有一个多图，其中存储日期（自定义 class 对象）和浮点值。 然后，我通过为此 map 创建一个迭代器来创建一个 for 循环，以执行一些操作。 出于某种原因，我的 it->first 中的日期值永远不会从第一个日期改变。 但是我在其他功能中使用了这种完全相同的方法，并且效果很好。 可能的原因是什么？

代码：

multimap<Date, float> mapOption5Solar;
    multimap<Time, float> mapOption5Time;
    Vector<Time> timeVec;

    for(int i = 1; i < SIZE; i++)
    {
        mapOption5Solar.insert(make_pair(windlog[i].d, windlog[i].solar.GetSolar()));
        mapOption5Time.insert(make_pair(windlog[i].t, windlog[i].solar.GetSolar()));
    }

    float maxVal = 0;
    cout << "Original values: " << maxVal << endl;
    for(std::multimap<Date, float>::iterator it = mapOption5Solar.begin(); it!=mapOption5Solar.end(); it++)
    {
        //cout << "Entered Date: " << entryDate << " Vector Date: " << it->first << endl;
        //cout << "CheckDate Day: " << checkDate.GetDay() << endl;
        //cout << "CheckDate Month: " << checkDate.GetMonth() << endl;
        //cout << "CheckDate Year: " << checkDate.GetYear() << endl;
        //cout << "it Day: " << it->first.GetDay() << endl;
        //cout << "it Month: " << it->first.GetMonth() << endl;
        //cout << "it Year: " << it->first.GetYear() << endl;
        if(checkDate == it->first)
        {
            if(it->second > maxVal)
            {
                maxVal = it->second;
                cout << "Just checking iterator value: " << it->second << endl;
            }
        }
    }
    cout << "Updated values: " << maxVal << endl;

CheckDate 是我创建的日期 object，用户在其中输入日期。 it->first 应该存储我的日期对象，但只打印出我输入的第一天的值，用于所有迭代。

最小的可重现示例：

Date tempDate;
Date tempDate2;
Date tempDate3;
tempDate.SetDay("3");
tempDate.SetMonth("2");
tempDate.SetYear("2013");

tempDate2.SetDay("7");
tempDate2.SetMonth("1");
tempDate2.SetYear("2015");

tempDate3.SetDay("4");
tempDate3.SetMonth("2");
tempDate3.SetYear("2017");
//cout << "Date entered: " << checkDate << endl;

multimap<Date, float> mapOption5Solar;
mapOption5Solar.insert(make_pair(tempDate, 35));
mapOption5Solar.insert(make_pair(tempDate2, 56));
mapOption5Solar.insert(make_pair(tempDate3, 37));


float maxVal = 0;
Date checkDate;
checkDate.SetDay("4");
checkDate.SetMonth("2");
checkDate.SetDay("2017");
for(std::multimap<Date, float>::iterator it = mapOption5Solar.begin(); it!=mapOption5Solar.end(); it++)
{
    //cout << "Entered Date: " << entryDate << " Vector Date: " << it->first << endl;
    //cout << "CheckDate Day: " << checkDate.GetDay() << endl;
    //cout << "CheckDate Month: " << checkDate.GetMonth() << endl;
    //cout << "CheckDate Year: " << checkDate.GetYear() << endl;
    //cout << "it Day: " << it->first.GetDay() << endl;
    //cout << "it Month: " << it->first.GetMonth() << endl;
    //cout << "it Year: " << it->first.GetYear() << endl;
    if(checkDate == it->first)
    {
        if(it->second > maxVal)
        {
            maxVal = it->second;
            cout << "Just checking iterator value: " << it->second << endl;
        }
    }
}

日期.h：

#if !defined(_DATE_H)
#define _DATE_H

#include <iostream>
#include <string>
#include <tuple>

using namespace std;

    /**
     * @class Date
     * @brief  Manages and holds all dates
     *
     * This class is used to convert string from the input file into numerical values
     * and then store them as date values
     * @author Darren Fernando
     *
     * @date 05/05/2020 Darren Fernando, Started
     * @bug No bugs founds as of yet
     */
class Date
{
public:
    Date();
    Date(unsigned day1, unsigned month1, unsigned year1);

        /**
        * @brief A set method that is used to set the day value
        * It takes a string parameter and calls another method to convert it, and then assign it to the variable day
        * @param day1 - A string variable that is converted
        * @return void
        */
    void SetDay(string day1);

        /**
        * @brief A set method that is used to set the month value
        * It takes a string parameter and calls another method to convert it, and then assign it to the variable month
        * @param month1 - A string variable that is converted
        * @return void
        */
    void SetMonth(string month1);

        /**
        * @brief A set method that is used to set the year value
        * It takes a string parameter and calls another method to convert it, and then assign it to the variable year
        * @param year - A string variable that is converted
        * @return void
        */
    void SetYear(string year1);

        /**
        * @brief A get method that is used to get the day value by returning it
        * @return unsigned
        */
    unsigned GetDay() const;

        /**
        * @brief A get method that is used to get the month value by returning it
        * @return unsigned
        */
    unsigned GetMonth() const;

        /**
        * @brief A get method that is used to get the year value by returning it
        * @return unsigned
        */
    unsigned GetYear() const;

        /**
        * @brief A method that converts a string to an unsigned numerical value
        * @param time - A string parameter that is converted
        * @return unsigned
        */
    unsigned convertString(string date) const;

        /**
        * @brief A method that takes an input stream and perfoms some operations to set the date from this stream
        * This method isn't used but may be valuable later on
        * @param input - An input stream
        * @return void
        */
    void SetDate(istream &input);

        /**
        * @brief A method that takes an output stream and outputs it
        * This method isn't used but may be valuable later on
        * @param os - An output stream
        * @return void
        */
    void GetDate(ostream & os) const;
    unsigned GetDateRaw() const;

private:

    int day; /// Variable to store the day
    int month; /// Variable to store the month
    int year; /// Variable to store the year

};

bool operator==(const Date& firstDate, const Date& secondDate);
bool operator>(const Date& firstDate, const Date& secondDate);
bool operator<(const Date& firstDate, const Date& secondDate);
bool operator!=(const Date& firstDate, const Date& secondDate);
ostream & operator <<(ostream & os, const Date & D); /// Operator << overload
istream & operator >>(istream & input, Date & D); /// Operator >> overload
#endif  //_DATE_H

日期.cpp：

//
//
//  Generated by StarUML(tm) C++ Add-In
#include "Date.h"

    // Default constructor
Date::Date(){}

    /* Date constructor to initialize an object of date with the passed parameters
    */
Date::Date(unsigned day1, unsigned month1, unsigned year1) {

    day = day1;
    month = month1;
    year = year1;

}

void Date::SetDay(string day1) {

    day = convertString(day1); // Calls method convertString to convert the string parameter and assign the new value to day.

}

void Date::SetMonth(string month1) {

    month = convertString(month1); // Calls method convertString to convert the string parameter and assign the new value to month.

}

void Date::SetYear(string year1) {

    year = convertString(year1); // Calls method convertString to convert the string parameter and assign the new value to year.

}

unsigned Date::GetDay() const {

    return day; // Returns the day of the object

}

unsigned Date::GetMonth() const {

    return month; // Returns the month of the object

}

unsigned Date::GetYear() const {

    return year; // Returns the year of the object

}

    /* This method is used for directly setting the date from a file. It is not used now,
    but may prove handy in the future.*/
void Date::SetDate(istream &input){

    string day1;
    string month1;
    string year1;


    getline(input, day1, '/'); //Reads line until '/' is found and stores the string in day1
    getline(input, month1, '/'); //Reads line until '/' is found and stores the string in month1
    getline(input, year1, ' '); //Reads line until ' ' is found and stores the string in year1

    /*Sets the strings with setters which convert them automatically
    */
    SetDay(day1);
    SetMonth(month1);
    SetYear(year1);


}
    //This method is designed to convert a string to an integer
inline unsigned Date::convertString(string date) const{

    int date2 = 0;

    date2 = stoi(date); //Uses stoi from cmath library to convert a string to an integer

    return date2;

}

    // A get function that uses the overloaded output stream to output the date in a specific format.
void Date::GetDate(ostream &os) const{

    os << GetDay() << "/" << GetMonth() << "/" << GetYear() << " ";

}

bool operator==(const Date& firstDate, const Date& secondDate)
{
    if(firstDate.GetYear() == secondDate.GetYear() && firstDate.GetMonth() == secondDate.GetMonth() && firstDate.GetDay() == secondDate.GetDay())
    {

        return true;

    }
    else
    {
        return false;
    }

}

/*bool operator!=(const Date& firstDate, const Date& secondDate)
{
    if(firstDate!=secondDate)
    {
        return true;
    }
    return false;
}*/

bool operator>(const Date& firstDate, const Date& secondDate)
{
    if(firstDate.GetYear() > secondDate.GetYear())
    {
        return true;
    }
    else
        if(firstDate.GetYear() < secondDate.GetYear())
        {
            return false;
        }
        else
        {
            if(firstDate.GetMonth() > secondDate.GetMonth())
            {
                return true;
            }
            else
                if(firstDate.GetMonth() < secondDate.GetMonth())
                {
                    return false;
                }
                else
                {

                    if(firstDate.GetDay() > secondDate.GetDay())
                    {
                        return true;
                    }
                    else
                    {
                        return false;
                    }
                }
        }
}



    // Input stream operator overload
istream & operator >>( istream & input, Date & D) {

    D.SetDate(input);
    return input;

}
    // Output stream operator overload
ostream & operator <<( ostream & os, const Date & D) {

    D.GetDate(os);

    return os;

}

1 个解决方案

解决方案1
 0  2020-06-09 08:40:26

由于您的代码（已修改以适应缺少的信息）工作正常，我只能认为您的问题在于您填充多图的内容。

具体来说，代码：

#include <iostream>
#include <map>

using namespace std;

int main() {
    multimap<int, float> mapOption;

    for(int i = 1; i < 5; i++) {
        mapOption.insert(make_pair(i, i / 100.0));
    }

    auto maxVal = 0.0f;
    cout << "Original values: " << maxVal << endl;
    for(auto it = mapOption.begin(); it != mapOption.end(); it++) {
        if(it->second > maxVal) {
            maxVal = it->second;
            cout << "Just checking iterator value: " << it->second << endl;
        }
    }
    cout << "Updated values: " << maxVal << endl;
}

输出正确的项目没有问题：

Original values: 0
Just checking iterator value: 0.01
Just checking iterator value: 0.02
Just checking iterator value: 0.03
Just checking iterator value: 0.04
Updated values: 0.04

因此，您可能应该首先在将项目放入多地图时转储它们，例如：

for(int i = 1; i < SIZE; i++) {
    auto one = windlog[i].d;
    auto two = windlog[i].solar.GetSolar();
    cout << "Inserting " << one << " : " << two << '\n';
    mapOption5Solar.insert(make_pair(one, two));
}

对于您更新的代码，我可以看到它不起作用的一个原因（除了它实际上不会以其当前形式编译的事实）。

您限制使用checkDate打印的内容，因此，根据您的输入（或您认为的内容），您只会看到一个项目，即与日期匹配的项目。 但是，由于以下代码，您甚至不会看到：

checkDate.SetDay("4");
checkDate.SetMonth("2");
checkDate.SetDay("2017");  // This is probably too big for a day :-)

我建议您将最后一行更改为SetYear试。

而且，经过一番努力（添加缺少的函数），它将编译并生成它似乎想要的结果。 我会提到你的代码相当冗长，可以清理很多，所以我借此机会这样做：

#include <iostream>
#include <map>

using namespace std;

// Nominal date.h

class Date {
public:
    Date();
    Date(unsigned day1, unsigned month1, unsigned year1);
    void SetDate(unsigned day1, unsigned month1, unsigned year1);
    unsigned GetDay() const;
    unsigned GetMonth() const;
    unsigned GetYear() const;
    void SetDate(istream &input);
    void GetDate(ostream & os) const;
private:
    unsigned day;
    unsigned month;
    unsigned year;
};

bool operator==(const Date& firstDate, const Date& secondDate);
bool operator>(const Date& firstDate, const Date& secondDate);
bool operator<(const Date& firstDate, const Date& secondDate);
bool operator!=(const Date& firstDate, const Date& secondDate);

// Nominal date.cpp

Date::Date(unsigned day1 = 0, unsigned month1 = 0, unsigned year1 = 0)
    : day(day1), month(month1), year(year1) {}

void Date::SetDate(unsigned day1, unsigned month1, unsigned year1) {
    day = day1;
    month = month1;
    year = year1;
}

unsigned Date::GetDay() const { return day; }
unsigned Date::GetMonth() const { return month; }
unsigned Date::GetYear() const { return year; }

void Date::SetDate(istream &input) {
    string day1;
    string month1;
    string year1;

    getline(input, day1, '/');
    getline(input, month1, '/');
    getline(input, year1, ' ');

    SetDate(stoi(day1), stoi(month1), stoi(year1));
}

void Date::GetDate(ostream &os) const {
    os << GetDay() << "/" << GetMonth() << "/" << GetYear() << " ";
}

bool operator==(const Date& firstDate, const Date& secondDate) {
    return firstDate.GetYear() == secondDate.GetYear()
        && firstDate.GetMonth() == secondDate.GetMonth()
        && firstDate.GetDay() == secondDate.GetDay();
}

bool operator!=(const Date& firstDate, const Date& secondDate) {
    return ! (firstDate == secondDate);
}

bool operator>(const Date& firstDate, const Date& secondDate) {
    if(firstDate.GetYear() > secondDate.GetYear()) return true;
    if(firstDate.GetYear() < secondDate.GetYear()) return false;
    if(firstDate.GetMonth() > secondDate.GetMonth()) return true;
    if(firstDate.GetMonth() < secondDate.GetMonth()) return false;
    return firstDate.GetDay() > secondDate.GetDay();
}

bool operator<(const Date& firstDate, const Date& secondDate) {
    return ! (firstDate > secondDate || firstDate == secondDate);
}

// Nominal test program.

int main() {
    Date tempDate(3, 2, 2013);
    Date tempDate2(7, 1, 2015);
    Date tempDate3(4, 2, 2017);

    multimap<Date, float> mapOption5Solar;
    mapOption5Solar.insert(make_pair(tempDate, 35));
    mapOption5Solar.insert(make_pair(tempDate2, 56));
    mapOption5Solar.insert(make_pair(tempDate3, 37));

    auto maxVal = 0f;
    Date checkDate(4, 2, 2017);
    for (auto it = mapOption5Solar.begin(); it != mapOption5Solar.end(); ++it) {
        if (checkDate == it->first) {
            if (it->second > maxVal) {
                maxVal = it->second;
                cout << "Just checking iterator value: " << it->second << '\n';
            }
        }
    }
}

我不怀疑可能还有其他改进，但我会把它作为练习留给你:-)

暂无
暂无

声明:本站的技术帖子网页，遵循CC BY-SA 4.0协议，如果您需要转载，请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.

相关问题 C ++多映射迭代器无效 C++：声明多映射迭代器时出错 在C ++中获取多图的价值 使用Multimap时C ++映射/设置迭代器不增加错误 如何将 c++ std::list 元素转换为多映射迭代器 在C ++中插入多对映射值的对中 如何在MultiMap C ++中删除重复值？ 检查Multimap C ++中是否已经存在值 C ++多图操作 C ++案例多图
相关标签
 
粤ICP备18138465号  © 2020-2024 STACKOOM.COM