C++ 中的读访问冲突

Question

That is my error. I try to keep it a little bit more organized in what code I provide and what I don't. In general, I am writing a C++ OpenGL application that can test, if two figures layed out with matchsticks match. I do the interaction by a Test class, which only is the way I can create graphical interfaces on top of my OpenGL interface. Important here are the following lines of code:

Figure fig1 = Figure();
Figure fig2 = Figure();
Figure* selected;

I have two figure objects, and one pointer. I can select either 1 or 2 in an ImGui overlay, which will in turn set the selected pointer to fig1 or fig2 . I then do tests for mouse events, and if the mouse is clicked I can calculate the x and y position of the point I clicked. That works perfectly.

I then want to add a new line object in my figure. My figure is saved as a set of lines in a std::vector<line> . For reference, I will add my whole figure header in the end. For now, I call these two functions when the mouse is pressed:

selected->SetWorking(posX, posY, m_Select);     //         
                                                // -> HIER STECKT NH 
if (m_Select)                                   //        FEHLER
    selected->AddLine();

As I understand, I now call the two functions on the object pointed to by the selected pointer. I will just show what happens after calling SetWorking() , which is where the exception originally is thrown. If I exclude both of the method calls, the program runs perfectly. If I have either one of them or both executed, this error is thrown.

void Figure::SetWorking(int x, int y, bool segment)
{
    if (segment)
    {
        p1 = Point(x, y);
    }
    p2 = Point(x, y);
}

This is my implementation of the function. The segment is not really important for the problem. Segment selects whether the first point of a line, or the second is to be edited. It just alternates: if I click once, the first point is edited. Then, after clicking the second time, the second is edited. With the right point selected, I try to build a pair of the calculated x and y coordinates, and when building the pair, the exception is thrown:

write access violation.
this was 0x18.

My Figure header:

#pragma once
#include <Windows.h>
#include <vector>
#include <Defines.h>



class Point
{
public:
    std::pair<int, int> coord;
    Point()
    {
        coord = std::pair<int, int>{ 0, 0 };
    }
    Point(int x, int y)
    {
        coord = std::pair<int, int>{ x, y };
    };
};

class Line
{
public:
    std::pair<Point, Point> pts;
    Line()
    {
        pts = std::pair<Point, Point>{ Point(), Point() };
    }
    Line(Point p1, Point p2)
    {
        pts = std::pair<Point, Point>{ (Point)p1, (Point)p2 };
    };
};

class Figure
{

private:
    std::vector<Line> lines;
    Point p1 = Point();
    Point p2 = Point();
    char* renderPath = FILEPATH;
public:
    Figure() {};
public:
    void DrawComponents();
    void Clear();
    void RemoveLine(int index);
    void AddLine();
    void SetWorking(int x, int y, bool segment); //true seg1, false seg2
    
    //void Render();
    
};

Answer 1

我只是忘了在构造函数中设置指针。