How to avoid successive deallocations/allocations in C++?

Question

Consider the following code:

class A
{
    B* b; // an A object owns a B object

    A() : b(NULL) { } // we don\'t know what b will be when constructing A

             


        

Answer 1

Like the others have already suggested: Try placement new..

Here is a complete example:

#include 
#include 

class B
{
  public:
  int dummy;

  B (int arg)
  {
    dummy = arg;
    printf ("C'Tor called\n");
  }

  ~B ()
  {
    printf ("D'tor called\n");
  }
};


void called_often (B * arg)
{
  // call D'tor without freeing memory:
  arg->~B();

  // call C'tor without allocating memory:
  arg = new(arg) B(10);
}

int main (int argc, char **args)
{
  B test(1);
  called_often (&test);
}