Question

Suppose I have a C++ class with two private variables. A fixed size array, data, and a pointer to that array, pnt.

class MyClass
{
   private:
      double *pnt;
      double data[2];
   public:
      myClass();
      virtual ~MyClass();
      double* getPnt() const;
      void setPnt(double* input);
};

MyClass::MyClass()
{

   double * input;
   data[0] = 1;
   data[1] = 2;

   input= data;
   setPnt(input);
}

MyClass::~MyClass()
{
 delete this->pnt; // This throws a runtime error
}


void MyClass::setPnt(double * input)
{
   pnt = input;
}

double * MyClass::getPnt() const;
{
   return pnt;
}

int main()
{
   MyClass spam; // Construct object
   delete spam; // Error C2440: 'delete' cannot convert from 'MyClass' to 'void*'
}

There are two problems with this code. First if I try to call delete on the object, I get:

Error C2440: ‘delete’ cannot convert from ‘MyClass’ to ‘void*’

Secondly, if I comment out the delete statement, I get a realtime error stating a debug assertion failed! and this:

Expression: _BLOCK_TYPE_IS_VALID(pHead->nBlockUse)

My question is then: For a class with a pointer to a private fixed size array, how do I properly free memory, write/call the destructor?

P.S I can’t use vector or nice containers like that (hence this question).

Answer 1

I see no static array. I see a fixed-size array. Also memory for data is allocated as part of the object.

You must not explicitely delete a member of the class: the delete operator will take care of that IFF the instance was dynamically allocated.

 {
      MyClass x; // auto variable
 } // x destructor run, no delete operator

vs.

 {
      MyClass* x = new MyClass(); // heap allocation variable
      delete x; // x destructor run, ::delete de-allocates from heap
 }