CODEWITHSUNDEEP
c++
anshul garg
anshul garg

Reputation: 503

Derived Class Member Initialization by base class constructor

I have one doubt regarding this code that this code is not correct. it can crash at run time.As p pointer is pointing to address of derived class member variable(char array) but before derived class constructor base class constructor gets called so memory initialization and allocation for derived class is not yet done. So when in base class constructor we do strcpy this code might crash.

class Base
{
 public: 
  char *p;
  Base(){};
  Base(char *a):p(a)
  {
     sprintf(a,"HELLO");
  };
};
class Derived:public Base
{
 public:
 char arr[10];
 Derived():Base(arr)
 {

 };

};

int main()
{
   Derived d = new Derived();
return 0;
}

From This code what i intend to do is to give address of char array to base class where some string needs to be written on address passed. But i am not sure this code will work always. Please clarify.

Upvotes: 0

Views: 923

Answers (1)

Mike Seymour
Mike Seymour

Reputation: 254431

This is well-defined, but fragile - it can break if you change the type of arr.

Storage is allocated for the complete object before running any constructor and, since arr has trivial initialisation, its lifetime begins as soon as storage has been allocated. It's therefore usable in the Base constructor.

If it were a non-trivial type, like std::string, then it wouldn't be usable in the Base constructor, and you'd have undefined behaviour.

Upvotes: 4

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