创建对象的第二个实例会更改整个类的行为(C ++) [英] Creating a second instance of an object changes whole class behavior (C++)

问题描述

我用C ++编写了一个Arduino库，其中包含一个迭代器类.如果我一直使用同一实例遍历它，那么它将按预期工作.如果我创建第二个实例，它将使存储的对象数量增加一倍.

I have written an Arduino library in C++ that contains an iterator class. If I iterate through it using the same instance all the time, it works as expected. If I create a second instance to do so, it will double the amount of stored objects.

WayPointStack wps = *(new WayPointStack());
wps.AddWP(1, 20);
wps.AddWP(2, 420);

WPCommand c1 = wps.GetNextWP(); //  Stack length: 2, correct
c1 = wps.GetNextWP();           //

WPCommand c1 = wps.GetNextWP(); //  Stack length: 4, not correct
WPCommand c2 = wps.GetNextWP(); //


  WPCommand WayPointStack::GetNextWP()
{
    Serial.println("Pointer = ");
    Serial.println(pointer);
    Serial.println("Length = ");
    Serial.println(_length);
    if (pointer < _length){
        pointer++;
        return _wp[pointer-1];
    }
    return *(new WPCommand(_END, 10000));
}

void WayPointStack::AddWP(int target, int time)
{
    if (_length == arrSize)
        return;
    _wp[_length] = *(new WPCommand(target, time));
    _length++;
}

WayPointStack::WayPointStack()
{
  _wp = new WPCommand[arrSize];
  _length = 0;
  pointer = 0;
}

WPCommand::WPCommand(int target, int time)
{
    _target = target;
    _time = time;
}

有人可以向我解释吗?

推荐答案

WayPointStack wps = *(new WayPointStack());

必须

WayPointStack wps;

因为这足够了，并且可以消除内存泄漏

because it is enough and that removes the memory leak

在

 WPCommand WayPointStack::GetNextWP()
 {
     ...
     return *(new WPCommand(_END, 10000));
 }

您创建了另一个内存泄漏，可能是不返回该元素，但其地址允许您在出错时返回nullptr?

you create an other memory leak, may be do not return the element but its address allowing you to return nullptr on error ?

 /*const ?*/ WPCommand * WayPointStack::GetNextWP()
 {
     Serial.println("Pointer = ");
     Serial.println(pointer);
     Serial.println("Length = ");
     Serial.println(_length);
     if (pointer < _length){
       return &_wp[pointer++];
     }
     return nullptr;
 }

否则使用静态var:

  WPCommand WayPointStack::GetNextWP()
  {
      ...
      static WPCommand error(_END, 10000);
      return error;
  }

---

在

---

In

void WayPointStack::AddWP(int target, int time)
{
    if (_length == arrSize)
        return;
    _wp[_length] = *(new WPCommand(target, time));
    _length++;
}

您创建了另一个内存泄漏，只需要初始化条目即可:

you create an other memory leak, you just need to initialize the entry :

 void WayPointStack::AddWP(int target, int time)
 {
     if (_length == arrSize)
         return;
     _wp[_length]._target = target, time));
     _wp[_length]._time = time;
     _length++;
 }

当您无法添加新元素时，您不会发出错误信号，返回 bool 会在错误时返回false，并在添加时返回true:

you do not signal the error when you cannot add a new element, what about to return a bool valuing false on error and true when you can add :

 bool WayPointStack::AddWP(int target, int time)
 {
     if (_length == arrSize)
         return false;
     _wp[_length]._target = target;
     _wp[_length]._time = time;
     _length++;
     return true;
 }

---

最后，为什么不将std::vector用作_wp

---

Finally Why do you not use a std::vector for _wp

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