我收到错误：尝试在地图中放置对象时，没有用于初始化std :: pair的匹配构造函数

如何解决我收到错误：尝试在地图中放置对象时，没有用于初始化std :: pair的匹配构造函数

我尝试将自定义类型“锻炼”作为键，将Stroustrup的Graph_lib中的Open_polyline填充到地图中，没有任何运气。插入对象对我没有帮助。

地图中每对键和值都必须具有默认构造函数吗？

我得到的错误如下：

C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.25.28610\include\xmemory(671,76): error: no matching constructor for initialization of 'std::pair<const Exercise,Graph_lib::Open_polyline>' 
::new (const_cast<void*>(static_cast<const volatile void*>(_Ptr))) _Objty(_STD forward<_Types>(_Args)...);

出现问题的功能：

graphs是类型map<Exercise,Open_polyline>的成员。

void WorkoutManager::updateGraphs(const bool state) {

    if (state) {
        
        for (auto w : loadedWorkouts) {
            // Date indicates location on x axis.
            // Each workout type gets its own graph.
            // Each weight of workout indicates location on y axis.
            
            int x_coord = stoi(date::format("%d",w.getDate().day()));
            const set<ExerciseSet> exs = w.getResults();
            
            int i {0}; // For Color picking.
            for (ExerciseSet es : exs) {
                // If exercise is found in map,point is added to existing graph.
                if (graphs.find(es.type) != graphs.end()) {
                    graphs.find(es.type)->second.add(Point{x_coord,es.weight});
                }
                
                else {
                    // Exercise not found: creates new graph.
                    Open_polyline opl;
                    opl.set_style(Line_style::solid);
                    opl.set_color(Color(i));
                    opl.add(Point{x_coord,es.weight}); // Adds new point to graph.

                    graphs.emplace(es.type,opl); // <-- ERROR HERE!
                }

                ++i;
            }
        }

        for (auto it = graphs.begin(); it != graphs.end(); ++it) {
            attach(it->second);
        }
    }
    else {
        // graphs.empty(); // <-- This also gives error.
    }
}

Shape从Open_polyline继承的Graph.h类。 这里只显示类及其构造函数。

class Shape
{ // deals with color and style,and holds sequence of lines
protected:
    Shape()
    {}

    Shape(initializer_list<Point> lst)
    {
        for (Point p : lst)
            add(p);
    } // add() the Points to this Shape
    
    ...
};

struct Open_polyline : Shape
{ // open sequence of lines
    using Shape::Shape;
    
    ...
};

Exercise枚举和ExerciseSet类：

#pragma once

#include <set>
#include <iostream>
#include <string>
#include <fstream>
#include "date.h" // Substitute for C++20 <chrono> which was not released yet.

using namespace std;

// Enumeration for exercises.
enum Exercise {
    ArnoldPress,BenchPress,BenchPressIncline,BenchPressDecline,BicepsCurl,CableFlies,Deadlift,EZBarCurl,HammerCurl,LatPullDown,LatRaise,LegCurl,LegExt,LegPress,Pulley,ShoulderPress,Squat,StandingRow,TriBenchExt,TriPullDownBar,TriPullDownRope
};

// Class to give a exercise a corresponding weight.
struct ExerciseSet {
    Exercise type;
    int weight;

    ExerciseSet(Exercise type,int weight) : type{type},weight{weight} {}

    // Required to add this class to a set.
    bool operator<(const ExerciseSet& r) const;
    bool operator==(const ExerciseSet& r) const;
};

解决方法

根据对这篇文章的评论，问题在于 Open_polyline 类缺少复制构造函数。我自己解决这个问题的方法是使用指向 Open_polyline 对象的指针，将它们放置在 map 内。