c++ - 在 C++ 中重新分配堆栈上的对象

Question

我来自 Java，发现某些对象非常困惑。

在我的代码中，我有一个具有 Cell 属性的事件类。当我创建一个新事件时，我想在不使用“new”关键字的情况下初始化单元格。代码如下。在 Event 的构造函数中，我能想到的就是放置“currentCell = new Cell()”。有没有什么方法可以在不这样做的情况下初始化 currentCell？

更一般地说，如果我有一个像 currentEvent 这样的对象，我怎样才能刷新它以获得不同的信息？假设 currentEvent 有单元格 a 和时间点 10，现在我希望它存储单元格 b 和时间点 12。在 java 中我会这样做:

Event e1 = new Event(a, 10);
e1 = new Event(b, 12);

但我想在 c++ 中做同样的事情而不把任何东西放在堆栈上。

这是事件头文件:

class Event {
public:
    Event();
    int getTime() { return timePoint; }
    void setTime(int newTime); 
    void setCell(Cell & newCell);
    virtual ~Event();
private:
    Cell * currentCell; //Class is made up of a pointer to a cell and a time
    int timePoint;
};

以及Event.cpp中的构造函数:

Event::Event()
{
    //Cell currentCell;
    currentCell = new Cell();  //don't want to use new, but do what to initialize currentCell to a blank new cell
    timePoint = rand() % 6 + 5;
}

一般问题:

priority_queue<Event, vector<Event>, CompareEvent> events;
Event firstEvent(*start, time); 
events.push(firstEvent);
Event * newEvent1; //I want to reassign newEvent1 and newEvent2 each time through the loop but would rather not have to use the heap
Event * newEvent2;

//temp int counter
int counter = 0;

while ((!(events.empty())) && (counter<5000)){

    //Get next event
    currentEvent = events.top();
    currentCell = currentEvent.getCell();
    if (currentCell->isAlive()) {

        bool canGrow = false;
        if (currentCell->selfGrows() || currentCell->withinRange()){
            canGrow = true;
        }

        if (canGrow){

            //Perform mitosis

            //Create a daughter cell and add it to the list; increment counter
            daughterCell = new Cell(*currentCell); 

            newEvent1 = new Event(*daughterCell, time, newDir);
            events.push(*newEvent1);

            }

        }
    }

Answer 1

没有指向 Cell 的指针，只有一个成员 Cell。它将在构造包含 Event 对象的过程中构造。

class Event {
public:
    Event();
    int getTime() { return timePoint; }
    void setTime(int newTime); 
    void setCell(Cell & newCell);
    virtual ~Event();
private:
    Cell currentCell; // <-- no need to have this as a pointer (asterisk removed)
    int timePoint;
};